Journal of Colloid And Interface Science (v.345, #2)
Cover 1 (OFC).
Monodisperse, high refractive index, highly charged ZnS colloids self assemble into crystalline colloidal arrays by Jia Luo; Dan Qu; Alexander Tikhonov; Justin Bohn; Sanford A. Asher (131-137).
We developed an efficient synthesis of monodisperse, highly surface charged, high refractive index ZnS spherical particles by using a gel–sol method. Concentrated solutions of zinc–ammonia–NTA (nitrilotriacetic acid) were reacted with thioacetamide in the presence of gelatin which stabilized the growing particles. We dramatically increased the particle surface charge density by condensing silica and silylated phosphonate groups on the particle surface. These monodisperse highly charged ZnS particles are somewhat porous and have a refractive index of 1.868. These are the highest refractive index, monodisperse, highly charged spherical particles to self assemble into non-close-packed crystalline colloidal arrays which Bragg diffract light.
Keywords: Monodisperse; Surface charge; High refractive index; Photonic crystal;
Dispersion and diameter separation of multi-wall carbon nanotubes in aqueous solutions by M. Bystrzejewski; A. Huczko; H. Lange; T. Gemming; B. Büchner; M.H. Rümmeli (138-142).
Multi-wall carbon nanotubes were effectively dispersed in aqueous solutions of anionic surfactants even below their CMC. The choice of surfactant influences the diameter distribution of the dispersed nanotubes.Comparative studies on dispersing of multi-wall carbon nanotubes (CNTs) using two anionic surfactants (sodium dodecyl sulphate, SDS, and sodium dodecyl benzenosulfonate, SDBS) are presented. The studies were conducted on the surfactant concentrations that were close to the critical micelle concentration (CMC). The stability of CNTs suspensions obtained for surfactant solutions at concentrations lower than the CMC was investigated. It was also found that the surfactant structure has an influence on the diameter distribution of dispersed CNTs.
Keywords: Carbon nanotubes; Dispersions; Surfactants; CMC; SDS; SDBS;
Chemical and physical characterizations of spinel ferrite nanoparticles containing Nd and B elements by Takashi Iwamoto; Yuki Komorida; Masaki Mito; Atsushi Takahara (143-148).
TEM photograph and size distribution histogram of representative spinel ferrite nanoparticles containing Nd and B elements. Mean diameter is 5.1 nm and standard deviation is 1.0 nm.We first succeeded in synthesizing ferrite nanoparticles containing Nd and B elements by a chemical route using a polyol process. The lattice constants of the ferrite nanoparticles were equivalent to 8.39 Å of the lattice constant for Fe3O4 with the spinel structure in a bulk state independently of the size in diameter and composition (Fe:Nd:B). The size in diameter was actually dominated by the amount of ligands (oleic acid and oleylamine) coating the nanoparticles and easily tuned by changing refluxing-time under reaction. The spinel-structured ferrite nanoparticles containing Nd and B elements showed large coercivity as compared to Fe3O4 nanoparticles with the spinel structure, which were prepared by the same chemical method. By doping Nd and B elements into the spinel structure of ferrite, magnetic anisotropy increased in comparison with Fe3O4 nanoparticles. According to the analysis of magnetization curve using the modified Langevin function, the ferrite nanoparticles displayed the coexistence of superparamagnetic and antiferromagnetic phases. The ferrite nanoparticles containing Nd and B elements exhibited magnetic core/shell structure on the basis of various magnetic properties. The interface effect between the superparamagnetic core and antiferromagnetic shell might enhance the effective magnetic anisotropy of the ferrite nanoparticles containing Nd and B elements.
Keywords: Ferrite; Nanoparticles; Spinel structure; Diameter dependence; Core–shell model; Modified Langevin equation; Superparamagnetic phase; Antiferromagnetic phase; Surface layer; Structural translation symmetry;
Alteration of magnetic and optical properties of ultrafine dilute magnetic semiconductor ZnO:Co2+ nanoparticles by Prashant K. Sharma; Ranu K. Dutta; Avinash C. Pandey (149-153).
Photoluminescence spectra and M–H loop for as synthesized ZnO:Co nanoparticles. (a) For RCo 2, i.e. 2%, (b) for RCo 4, i.e. 5%, (c) for RCo 6, i.e. 10% and (d) for RCo 8, i.e. 20% Co-doped samples.Single-phase ZnO:Co2+ nanoparticles of mean size 2–8 nm were synthesized by a simple co-precipitation technique. X-ray diffraction analysis reveals that the Co-doped ZnO nanoparticles crystallize in wurtzite structure without any impurity phase. The wurtzite structure (lattice constants) of ZnO nanoparticles decrease slightly with increasing Co doping concentration. Optical absorption spectra show an increase in the band gap with increasing Co content and also give an evidence of the presence of Co2+ ions at tetrahedral sites of ZnO and substituted for the Zn site with no evidence of metallic Co. Initially these nanoparticles showed strong ferromagnetic behavior at room temperature, however at higher doping percentage of Co2+, the ferromagnetic behavior was suppressed, and antiferromagnetic nature was enhanced. The enhanced antiferromagnetic interaction between neighboring Co–Co ions suppressed the ferromagnetism at higher doping concentrations of Co2+. Photoluminescence intensity owing to the vacancies varies with the Co concentration because of the increment of oxygen vacancies.
Keywords: DMS; Ferromagnetism; VSM; Absorption; Photoluminescence spectroscopy;
Adsorption and desorption of antimony acetate on sodium montmorillonite by Zhenlu Zhao; Xiaoqun Wang; Chuan Zhao; Xiaoguang Zhu; Shanyi Du (154-159).
The adsorption of Sb(OAc)3 onto sodium montmorillonite (Na-MMT) was conducted with five initial Sb(OAc)3 concentrations at 120 °C. It was constructed by plotting the adsorbed amount of Sb(OAc)3 (C ads mol/g) versus the equilibrium concentration of Sb(OAc)3 in the solution (C w mol/l).The adsorption of antimony acetate (Sb(OAc)3) on sodium montmorillonite (Na-MMT) was studied at five different initial concentrations, and data from the adsorption isotherm were modeled using the Langmuir, Freundlich and D–R isotherm equations. The kinetics of adsorption was also discussed using three kinetic models: the pseudo-first-order, the pseudo-second-order and the intraparticle diffusion model. The rate constants of pseudo-first-order, pseudo-second-order and intraparticle diffusion kinetics, and the amount of Sb(OAc)3 adsorbed at equilibrium were determined. Moreover, the desorption of Sb(OAc)3 from several kinds of Sb-MMT (Na-MMT was intercalated by antimony acetate) was investigated at room temperature and 180 °C. The results show that according to the maximum amounts of adsorbate and correlation coefficients calculated from the three isotherm equations mentioned above, the corresponding data from adsorption experiments fit fairly well to the Langmuir isotherm. The adsorption data show a good compliance with the pseudo-second-order kinetic model and also follow the intraparticle diffusion model up to 30 min. The equilibrium adsorption capacity of Sb(OAc)3 on MMT is close to the cation exchange capacity (CEC) of the montmorillonite. The desorption amount of Sb(OAc)3 is correlated with both the temperature of desorption and the drying temperature of Sb-MMT.
Keywords: Antimony acetate; Montmorillonite; Adsorption; Desorption;
Chain length dependence of antimicrobial peptide–fatty acid conjugate activity by Alexander F. Chu-Kung; Rose Nguyen; Kristen N. Bozzelli; Matthew Tirrell (160-167).
Conjugation of increasing longer fatty acids to antimicrobial peptides improves their antimicrobial activity (solid lines). However, the improvement is limited by the self-assembly of the peptide conjugates above critical tail lengths.The rise of resistant bacteria has prompted the search for new antimicrobial agents. Antimicrobial membrane lytic peptides have potential as future microbial agents due to their novel mode of action. Recently conjugation of a fatty acid to antimicrobial peptides has been explored as a method to modulate the activity and selectivity of the peptide. Our work further explores these phenomena by testing two peptides, YGAAKKAAKAAKKAAKAA (AKK) and LKKLLKLLKLLKL (LKK), conjugated to fatty acids of varying length for their activity, structure, solution assembly properties and the ability to bind model membranes. We found that increasing the length of fatty acids conjugated to peptide AKK, up to a 16 carbons in length, increases the antimicrobial activity. Peptide AKK appears to lose activity when the minimal active concentration is higher than the critical miscelle concentration (CMC) of the molecule. Thus, if the CMC of the peptide conjugate is too low the activity is lost. Peptide LKK has no activity when conjugated to lauric acid and appears to aggregate at very low concentrations. Conjugation of AKK with a fatty acid increases its affinity to model supported lipid membranes. It appears that the increased hydrophobic interaction imparted by the fatty acid increases the affinity of the peptide to the surface thus increasing its activity. At concentrations above the CMC, solution self-assembly inhibits binding of the peptide to cell membranes.
Keywords: Antimicrobial peptide; Fatty acid; Conjugation;
Preparation and characterization of coverage-controlled CaCO3 nanoparticles by Yang Li; Zhong-fu Zhao; Yiu-Ting Richard Lau; Yong Lin; Chi-ming Chan (168-173).
CaCO3 nanoparticles coverage could be tuned with organic surfactants through a salt-exchange procedure and an extraction procedure, based on which the structures and properties of CaCO3/polymer nanocomposites could be controlled.CaCO3 nanoparticles were coated with stearate through a salt-exchange procedure. Their coverage had been successfully controlled by extraction in a Soxhlet apparatus, based on which a series of CaCO3 nanoparticles were obtained with different surface coverages. They were characterized with thermogravimetric analysis, X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. It was found that free stearate, intercalated stearate and chemically-bonded alkyl chains could be extracted sequentially with the Soxhlet apparatus. Thus, the coverages of CaCO3 nanoparticles could be adjusted through carefully extracting the stearates from the CaCO3 nanoparticles with multi-layer coverage. Spectroscopic results revealed that the alkyl chains tended to adopt an extended-chain conformation in the monolayer coverage as well as the bi-layer coverage, but less ordered conformation in partially-coated coverage and random orientation at the outmost surface of the coated nanoparticles.
Keywords: CaCO3 nanoparticles; Surface modification; Tuned coverage; Extraction;
Amperometric immunosensor for the determination of α-1-fetoprotein based on multiwalled carbon nanotube–silver nanoparticle composite by Xin Che; Ruo Yuan; Yaqin Chai; Jingjing Li; Zhongju Song; Jinfen Wang (174-180).
The schematic illustration of stepwise fabrication process of the immunosensor: BSA/anti-AFP/CS–MnO2/MWNTs–Ag/GCE.A new amperometric immunosensor for the determination of α-1-fetoprotein (AFP) has been constructed. First, a multiwalled carbon nanotube–silver (MWNT–Ag) composite was modified on the surface of a glassy carbon electrode. Then, chitosan–MnO2 (CS–MnO2) with excellent film forming ability was dipped onto the MWNT–Ag-modified electrode. Subsequently, gold nanoparticles were electrodeposited on the electrode to immobilize anti-AFP. The assembly processes were characterized with cyclic voltammetry, electrochemical impedance spectroscopy, and scanning electron microscopy. MWNT–Ag composite was characterized by transmission electron microscopy, X-ray photoelectron spectroscopy, and UV–vis spectroscopy. The system was optimized to realize a reliable determination of AFP in the range of 0.25–250 ng/ml with a detection limit of 0.08 ng/ml (S/N = 3). The proposed immunosensor showed a rapid and highly sensitive amperometric response to AFP with acceptable stability and reproducibility.
Keywords: Amperometric immunosensor; Multiwalled carbon nanotube–silver composite; MnO2; α-1-Fetoprotein;
Low-temperature and one-step synthesis of rutile TiO2 aqueous sol by heterogeneous nucleation method by Bin Qi; Liangzhuan Wu; Yang Zhang; Qinghui Zeng; Jinfang Zhi (181-186).
A phase-pure rutile TiO2 sol was synthesized by using the aqueous peroxotitanate solution as precursor at low temperature. The uniform and transparent films formed by the sol demonstrate a strong UV absorption.A phase-pure rutile TiO2 aqueous sol has been prepared by heterogeneous nucleation method with an aqueous peroxotitanate solution as a precursor and SnCl2 as rutile-phase crystalline growth promoter at a temperature as low as 100 °C in one-step process. TEM, XRD and UV–Vis spectra were used to characterize the rutile TiO2 sol. The results reveal that a pure rutile phase TiO2 aqueous sol with average particle sizes of around 20 nm has been synthesized, and a transparent film of rutile TiO2 was also easily prepared by dip-coating method. Formation conditions and a possible mechanism of phase-controlling were investigated. The results show that the presence of the Sn content is essential for the formation of a pure rutile TiO2 phase at low temperature, which involves a heterogeneous nucleation mechanism.
Keywords: Rutile TiO2 sol; Low-temperature synthesis; Peroxotitanate solution;
Silver nanoparticle monolayers on poly(ethylene imine) covered mica produced by colloidal self-assembly by Aneta Michna; Zbigniew Adamczyk; Barbara Siwek; Magdalena Oćwieja (187-193).
Uniform monolayer of silver nanoparticles deposited at PEI modified mica.Monodisperse silver particles were synthesized according to the method of Creighton et al. by reduction of AgNO3 solutions with NaBH4 in the presence of polyvinyl alcohol as the stabilizing agent. Bulk characteristics of silver nanoparticles in aqueous solutions were carried out by measuring their extinction spectrum, fluorescence, diffusion coefficients using the PCS method and the electrophoretic mobilities. The average hydrodynamic diameter of PVA covered silver particles was 44 nm, being fairly independent of ionic strength and pH in the range of 3–9. It was also shown that the hydrodynamic radius did not change within prolonged storage of suspensions (up to 75 days), indicating that the sols were quite stable. A similar value of 45 ± 8 nm was determined from SEM measurements. The electrophoretic mobility measurements showed that the zeta potential of silver nanoparticles was insensitive to pH and decreased with the ionic strength, attaining −45 mV for I = 10−5 M and −25 mV for I = 10−2 M. Additionally, the kinetics of silver particle deposition on mica modified by adsorption of a saturated layer of poly(ethylene imine) (PEI) was studied. Surface concentration was determined directly by counting the number of particles over various surface areas using the atomic force microscopy working in the semicontact mode. The maximum surface concentration for I = 10−3 M was 102 μm−2, which corresponds to the coverage degree of 16%. The kinetic run and the maximum coverage value was in a good agreement with theoretical predictions stemming from the random sequential adsorption (RSA) model. This kinetic run allowed one to determine the size of Ag core, which was 20 nm and the thickness of the PVA layer, equal to 12 nm.
Keywords: AFM measurements of silver nanoparticles deposition; Deposition of silver nanoparticles; Monolayers of silver nanoparticles on mica cover by PEI; PVA stabilized silver nanoparticles; Silver nanoparticles deposition;
Electrophoretic mobility of concentrated carbon black dispersions in a low-permittivity solvent by optical coherence tomography by Mehul N. Patel; P. Griffin Smith; Jihoon Kim; Thomas E. Milner; Keith P. Johnston (194-199).
The charge of carbon black particles with surfactant sodium bis(2-ethyl-1-hexyl)sulfosuccinate is measured using optical coherence tomography. A mechanism of particle charging is presented based on surfactant layering and cation partitioning.Electrophoretic mobilities of concentrated dispersions of carbon black particles in a low-permittivity solvent were measured using differential-phase optical coherence tomography (DP-OCT). An electrode spacing of only 0.18 mm enables measurement of highly concentrated dispersions up to 1 wt.% of highly absorbing carbon black particles with high electric fields at low potentials. The capabilities of this DP-OCT method, including high sensitivity, high spatial resolution, and strong electric fields, enable enhanced measurement of low electrophoretic mobilities encountered in low-permittivity solvents. The zeta potential of carbon black particles ranged from −24 mV to −12 mV as the concentration of surfactant sodium bis(2-ethyl-1-hexyl)sulfosuccinate (AOT) was increased from 1 mM to 100 mM. A mechanism is presented to explain the electrostatic charging of carbon black particles in terms of the partitioning of the ions between the reverse micelles in the double layer and the surfactant adsorbed on the particle surface, as AOT concentration is varied.
Keywords: Colloids; Carbon black; Electrostatic stabilization; Optical coherence tomography;
Direct synthesis and fluorescent imaging of bifunctionalized mesoporous iodopropyl-silica by Jan H. Ramm; Nando Gartmann; Dominik Brühwiler (200-205).
Bifunctionalized mesoporous silica containing iodopropyl moieties is prepared by an one-pot synthesis. Confocal laser scanning microscopy after fluorescent labeling reveals a homogeneous distribution of accessible functional groups.The cocondensation of 3-iodopropyltrimethoxysilane and tetraethoxysilane with an additional substituted trimethoxysilane (RTMS) in the presence of Pluronic P123 and hydrogen iodide yields bifunctionalized mesoporous silica. The pore-size distribution of these materials depends on the nature of the RTMS additive. Excellent results in terms of a narrow pore-size distribution were obtained with methyltrimethoxysilane. A particularly interesting bifunctionalized mesoporous material is formed by the coinclusion of iodopropyl and aminopropyl moieties. The complementary reactivity of these two functional groups is demonstrated by the selective labeling of the amino-iodo-functionalized mesoporous silica with 2-hydroxy-substituted Nile red and fluorescein isothiocyanate, allowing further characterization of the functional group distribution by confocal laser scanning microscopy.
Keywords: Mesoporous silica; Cocondensation; Iodopropyl; Aminopropyl; Labeling; Confocal laser scanning microscopy;
Dynamic structure of humic substances: Rare earth elements as a fingerprint by Mathieu Pédrot; Aline Dia; Mélanie Davranche (206-213).
Dynamic structure of humic substances according to pH.Whereas humic substances are known to play a key role in controlling metal speciation and trace element mobility within soils and waters, the understanding of their structure is still unclear and remains a matter of debate. Several models of humic substance structure have been proposed, where humic substances were composed of either: (i) macromolecular polyelectrolytes that can form molecular aggregates or (ii) supramolecular assemblies (molecular aggregates) of small molecules without macromolecular character, joined together by weak attraction forces. This experimental study was designed and dedicated: (i) to follow the size of organic molecules versus ionic strength or pH by the combined means of ultrafiltration and aromaticity data and rare earth element (REE) fingerprinting, and (ii) to investigate the pH and ionic strength effect on the distribution of associated rare earth elements in soil solution. This study supports the presence of supramolecular associations of small molecules and probably the presence of macromolecules in the bulk dissolved organic matter. By contrast to ionic strength, pH appeared to be the major parameter playing on the stability of the humic substance structure. Humic substances displayed dynamic structures, which evolved with regard to pH. Low pH led to a destabilization of the humic substance conformation. This destabilization had an impact on the trace element distribution in soil solution, as assessed by REE data, and conversely, the destabilization degree of humic substances seemed to be influenced by the metal ion charge.
Keywords: Supramolecular association; Humic substances; Rare earth elements; pH; Ionic strength;
Surface characterization of functionalized latexes with different surface functionalities using rheometry and dynamic light scattering by Jan S. Vesaratchanon; Koichi Takamura; Norbert Willenbacher (214-221).
The thickness of the surface layer of styrene–butylacrylate latex functionalized either with acrylic acid (AA), methacrylic acid (MAA), itaconic acid (IA) or acrylamide (AM) is investigated. The extended surface layer of the acrylic acid modified latex is visualized by electron microscopy.Here we study the formation of sterically stabilizing “hairy” surface layers for a series of styrene–butylacrylate and styrene–butadiene latexes copolymerized either with acrylic acid (AA), methacrylic acid (MAA), itaconic acid (IA) or acrylamide (AM) using dynamic light scattering, steady shear and high frequency rheology. This phenomenon is investigated under different conditions of pH, ionic strength, and temperature. The AA copolymerized latex has the most extended hairy layer and is very sensitive to pH and ionic strength. MAA yields a thinner hairy layer than AA due to higher hydrophobicity. IA exhibits a hairy layer thickness of about 1 nm, since it terminates polymer chain growth. For the AM copolymerized latexes high frequency viscosity reveals the existence of a thin hairy layer and the high values of the low shear viscosity and the high frequency modulus are attributed to a weak, reversible flocculation. No significant effect of particle core composition or temperature on the formation of the hairy layer was observed. High frequency rheology is most valuable for characterization of surface layers of carboxylated latexes, since it provides not only direct information about the effective volume fraction but also characterizes the strength of colloidal interactions among particles and it is applied at high particle concentration relevant during manufacturing and processing.
Keywords: Carboxylated latex; High frequency rheology; Electrosteric stabilization; Colloidal dispersion; Dispersion stability;
Highly luminescent quantum dots functionalized and their conjugation with IgG by Ping Yang; Aiyu Zhang; Hongsheng Sun; Futian Liu; Qinghui Jiang; Xin Cheng (222-227).
A sol–gel approach was developed to prepare highly luminescent SiO2-coated CdTe quantum dots where they further conjugated with IgG using 3-sulfo-N-hydroxysuccinimide or streptavidin–maleimide as linkers.A sol–gel approach including partially removing capping agents, depositing SiO2 monomers, and growing a SiO2 shell was developed to generate a bio-compatible functionalization on CdTe quantum dots (QDs). The QDs retained their high photoluminescence (PL) efficiency after coating with a SiO2 shell (22.5%) by controlling the surface state of the QDs to decrease PL degradation during a sol–gel preparation. Furthermore, the CdTe QDs with a SiO2 shell were conjugated with IgG using 3-sulfo-N-hydroxysuccinimide or streptavidin–maleimide as linkers. The biotin–streptavidin linker resulted in a high PL efficiency retained (only ∼23% lower than the initial value of the QDs), which is crucial for bio-applications.
Keywords: Quantum dots; Silica; Luminescence; Functionalization; IgG;
Preparation and capacitance property of MnO2-pillared Ni2+–Fe3+ layered double hydroxides nanocomposite by Hongjuan Li; Gang Zhu; Zupei Yang; Zenglin Wang; Zong-Huai Liu (228-233).
Formation process of MnO2-pillared Ni2+–Fe3+ LDHs nanocomposite.A novel MnO2-pillared Ni2+–Fe3+ layered double hydroxides nanocomposite has been successfully fabricated using an intercalation/reduction reaction followed by heating treatment. The structural evolution of the samples obtained at different stages has been characterized by XRD, TEM, XPS, IR and N2 adsorption–desorption. The layered structure of MnO2-pillared Ni2+–Fe3+ layered double hydroxides nanocomposite can be maintained at 300 °C, and the obtained material has a large surface area of 202 m2 g−1. Electrochemical studies indicate that the material obtained by heating at 200 °C exhibits an ideal capacitive behavior and good cycling property in 1 mol L−1 Na2SO4 aqueous solution, and the specific capacitance value was 190 F g−1 at a scan rate of 5 mV s−1.
Keywords: Layered nanocomposite; Ni2+–Fe3+ layered double hydroxides; Intercalation/reduction reaction; Pillar; Specific capacitance;
Silica coated magnetite particles for magnetic removal of Hg2+ from water by Penka I. Girginova; Ana L. Daniel-da-Silva; Cláudia B. Lopes; Paula Figueira; Marta Otero; Vítor S. Amaral; Eduarda Pereira; Tito Trindade (234-240).
Fe3O4 colloidal particles with dithiocarbamate derivatized surfaces are reported. These systems behave as highly efficient eco-nanomagnets for Hg2+ uptake from water.The magnetic removal of Hg2+ from water has been assessed using silica coated magnetite particles. The magnetite particles were first prepared by hydrolysis of FeSO4 and their surfaces were modified with amorphous silica shells that were then functionalized with organic moieties containing terminal dithiocarbamate groups. Under the experimental conditions used, the materials reported here displayed high efficiency for Hg2+ uptake (74%) even at contaminant levels as low as 50 μg l−1. Therefore these eco-nanomagnets show great potential for the removal of heavy metal ions of polluted water, via magnetic separation.
Keywords: Mercury; Magnetite particles; Dithiocarbamate; Silica surfaces; Water purification;
Layer by layer chitosan/alginate coatings on poly(lactide-co-glycolide) nanoparticles for antifouling protection and Folic acid binding to achieve selective cell targeting by Jie Zhou; Gabriela Romero; Elena Rojas; Lie Ma; Sergio Moya; Changyou Gao (241-247).
Poly(lactide-co-glycolide) (PLGA) nanoparticles surface engineered with a self assembled Layer by layer chitosane and alginate film and Folic acid display selective targeting for cancer cell lines.Polyelectrolyte multilayers (PEMs) composed of two natural polysaccharides-chitosan (Chi) and alginate (Alg) were deposited by Layer by layer (LbL) assembly on top of biocompatible poly(lactide-co-glycolide) (PLGA) nanoparticles (NPs). Folic acid (FA) or FA grafted poly(ethylene glycol) (PEG–FA) were covalently bounded to the PEMs via carbodiimide chemistry. The assembly of biocompatible PEMs was monitored on planar surfaces by means of the quartz crystal microbalance with dissipation (QCM-D) technique and on top of PLGA NPs by means of ζ-potential measurements. BSA was used as model protein to characterize protein adsorption on PEMs. QCM-D showed protein deposition could not be observed on the Chi/Alg multilayer, for both Chitosan and Alginate as top layers. Finally, cellular uptake experiments were carried out by co-culture of HepG2 cells in presence of NPs. Flow Cytometry and confocal laser scanning microscopy (CLSM) were used to investigate the influence of the surface chemistry of the NPs on uptake. For the HepG2 cell line significantly less uptake of PLGA NPs coated with Chi/Alg than the bare NPs was observed but the uptake increased after attachment of FA molecules.
Keywords: Poly(lactide-co-glycolide) nanoparticles; Chitosane; Alginate; Layer by layer; Antifouling protection; Targeting; Cellular uptake;
Impact of the antimicrobial peptide Novicidin on membrane structure and integrity by Søren B. Nielsen; Daniel E. Otzen (248-256).
Mechanism of Novicidin (Nc) interaction with anionic membranes. At low concentrations, Nc binds in a surface bound state without causing leakage. At higher concentration, transient pores are initially formed although the overall integrity of the membrane is preserved. At higher Nc concentrations, the membrane is significantly disturbed and disintegrates in a detergent-like manner.We have studied the impact of an 18-residue cationic antimicrobial peptide Novicidin (Nc) on the structure and integrity of partially anionic lipid membranes using oriented circular dichroism (OCD), quartz crystal microbalance with dissipation (QCM-D), dual polarization interferometry (DPI), calcein dye leakage and fluorescence spectroscopy. OCD consistently showed that Nc is bound in an α-helical, surface bound state over a range of peptide to lipid (P/L) ratios up to ∼1:15. Realignment of Nc at higher P/L ratios correlates to loss of membrane integrity as shown by Laurdan fluorescence spectroscopy and by loss of lipid alignment in DPI analysis. Laurdan generalized polarity shows a decrease in water accessibility or mobility in the hydrophobic/hydrophilic interface of the lipid membrane, consistent with rearrangement of lipid packing. QCM-D studies on the interaction of Nc with lipid membranes emphasize the importance of including the dissipation factor in data analysis, revealing formation of a highly hydrated film after exposure to ⩾3 μM Nc. Our findings suggest a carpet mechanism of membrane disruption in which peptide binding first induces leakage at a critical surface concentration, probably through formation of transient pores or transient disruption of the membrane integrity, followed by more extensive membrane disintegration at higher P/L ratios.
Keywords: Quartz crystal microbalance with dissipation; Supported lipid bilayers; Antimicrobial peptide; Oriented circular dichroism; Calcein dye leakage;
Phase separation of organic/inorganic hybrids induced by calcination: A novel route for synthesizing mesoporous silica and carbon materials by Sen Liu; Zhe Zhang; Haiyan Zhang; Yonglai Zhang; Shu Wei; Limin Ren; Chunyu Wang; Yinyan He; Fei Li; Feng-Shou Xiao (257-261).
Mesoporous silica and carbon materials have been successfully synthesized via a novel calcination induced phase separation of organic/inorganic hybrids prepared from solvothermal polymerization of polyvinyl alcohol and tetraethyl orthosilicate in dimethyl sulfoxide.Mesoporous silica and carbon materials have been successfully synthesized via a novel calcination induced phase separation of organic/inorganic hybrids prepared from solvothermal polymerization of polyvinyl alcohol (PVA) and tetraethyl orthosilicate (TEOS) in dimethyl sulfoxide (DMSO). Combined characterizations of XRD, nitrogen isotherms, and TEM techniques show that the samples have worm-like mesostructures with uniform pore size distributions and large BET surface areas. 1H NMR spectra reveal that ethanol was generated after the solvothermal treatments, indicating the polymerization of PVA and TEOS. Open mesopores of the desired silicas or carbons could be fabricated by calcining the hybrids in air and nitrogen, respectively. This route might open a new methodology to synthesize mesoporous materials.
Keywords: Calcination; Organic/inorganic hybrids; Non-aqueous synthesis; Mesoporous silica; Mesoporous carbon; Phase separation;
Preparation and characterization of upconversion luminescent NaYF4:Yb, Er (Tm)/PS bulk transparent nanocomposites through in situ polymerization by Ruitao Chai; Hongzhou Lian; Ziyong Cheng; Cuimiao Zhang; Zhiyao Hou; Zhenhe Xu; Jun Lin (262-268).
The as-prepared β-NaYF4:17%Yb, 3%Er/PS and β-NaYF4:25%Yb, 0.3%Tm/PS nanocomposites show strong green and blue emission, respectively, upon 980 nm laser excitation. These nanocomposites can be potentially used as 3D display materials.The in situ polymerization method was applied to synthesize bulk nanocomposites consisting of hydrophobic NaYF4:Yb, Er (Tm) nanoparticles as the filler and polystyrene (PS) as the host material. The oleic acid stabilized NaYF4:Yb, Er (Tm) nanoparticles and NaYF4:Yb, Er (Tm)/PS nanocomposites have been well characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), the thermogravimetric analysis (TGA), upconversion photoluminescence spectra and luminescence decays. The well-crystallized NaYF4:Yb, Er (Tm) nanoparticles are spherical with a mean diameter of 40 nm. NaYF4:Yb, Er/PS and NaYF4:Yb, Tm/PS nanocomposites exhibit strong green and blue upconversion photoluminescence upon 980 nm laser excitation, due to the integration of luminescent NaYF4:Yb, Er and NaYF4:Yb, Tm nanoparticles, respectively. These nanocomposites can be potentially used as 3D display materials.
Keywords: Polystyrene (PS); NaYF4; Luminescence; Nanocomposite;
Regulation role of ibuprofen toward the morphology of porous silica nanospheres during its in situ encapsulation by Xin Du; Junhui He (269-277).
IBU-containing porous silica nanospheres of varied morphologies were fabricated simply by tailoring the amount of IBU in the starting solution by employing the emulsion sol–gel method.In this work, in situ encapsulation of ibuprofen (IBU) was explored preliminarily using the emulsion sol–gel method. IBU-containing porous silica nanospheres (300–400 nm) of varied morphologies were fabricated simply by tailoring the amount of IBU in the starting solution. In the reaction system, IBU exists in the form of IBU− under basic conditions, which has strong electrostatic interaction with CTA+, and thus could be regarded as cosurfactant to regulate the morphology and structure of silica nanospheres. Such morphology can be maintained even after calcination or IBU release in phosphate-buffered saline. The current results may shed light on the design and construction of new functional nanoarchitectures, which may be useful for drug delivery, separation, adsorption, catalysis, etc.
Keywords: Emulsion sol–gel method; Porous silica nanosphere; Ibuprofen; In situ encapsulation; Release behavior;
On the kinetics of acid sodium caseinate gelation using particle tracking to probe the microrheology by Thomas Moschakis; Brent S. Murray; Eric Dickinson (278-285).
Typical microstructural evolution of an acidified sodium caseinate solution containing carboxylate-modified microspheres obtained via CLSM.The sol–gel transition of a model dairy system (sodium caseinate solution) which undergoes gelation by acidification has been studied by conventional bulk rheology and particle tracking microrheology, via confocal microscopy. The Brownian diffusion of fluorescent microspheres (0.21, 0.32, 0.5, and 0.89 μm in diameter) with different surface coatings (polyethylene glycol, carboxylate groups and polystyrene) was used to probe spatial mechanical properties of the gels at the scale of microns. The microrheological results are compared with the macroscopic viscoelastic properties (storage and loss shear modulus) measured in a concentric cylinder rheometer (double gap, at shear strain of 0.005 and frequency of 1 Hz). At pH values close to pI of the caseins, where formation of a protein network, i.e., gelation, became obvious from the confocal microscopy and bulk rheological measurements, all the particles had a tendency to adhere to the network. In spite of this, the microrheological values of the moduli were only slightly lower than the macroscopically determined values and the gel points calculated via both techniques tended to be in good agreement. However, the particle tracking method has higher sensitivity and can detect changes in the structuring of the system before these are registered by the bulk rheological measurement.
Keywords: Particle tracking microrheology; Confocal microscopy; Acid sodium caseinate gels; Gel point;
Dual-action hygienic coatings: Benefits of hydrophobicity and silver ion release for protection of environmental and clinical surfaces by Niall Stobie; Brendan Duffy; John Colreavy; Patrick McHale; Steven J. Hinder; Declan E. McCormack (286-292).
Dual-action hygienic coating: surface immobilisation of a perfluoropolyether inorganic hybrid polymer with silver ion release to protect environmental and biomedical surfaces.Coatings that demonstrate reduced attachment of crystalline precipitates and the medical device colonising Staphylococcus epidermidis were prepared by the immobilisation of silver doped perfluoropolyether–urethane siloxane thin films on glass substrates. The presence of stratified hydrophobic perfluoropolyether groups protects the coating surface from the attachment of crystalline hydrophilic species such as chlorides and phosphates, whilst silver ion release inhibited attachment of S. epidermidis and subsequent biofilm formation in vitro. The release of silver ions protects the perfluoro groups from the hydrophobic interactions of S. epidermidis cells, which can reduce the hydrophobicity of the protective coating. These coatings also exhibited significant antibacterial activity against planktonic Acinetobacter baumannii and S. epidermidis bacterial strains. Detailed elemental and chemical surface analysis obtained using X-ray photoelectron spectroscopy (XPS) provided useful information on the effect of bacterial incubation on key indicator hydrophobic and hydrophilic functional groups. XPS analysis indicated preferential adsorption of S. epidermidis cells at the hydrophobic sites along the polymeric chain. These dual-action hygienic coatings can be employed to protect against contamination environmental surfaces and bacterial colonisation on implanted medical devices.
Keywords: Antibacterial; Biofilm; Coatings; Silver; Perfluoropolyether; Hybrid;
Structure of the SDS/1-dodecanol surfactant mixture on a graphite surface: A computer simulation study by Hector Domínguez (293-301).
SDS/dodecanol mixtures on a graphite plate. At low concentration the molecules form well defined layers whereas at high concentration they form a monolayer.Molecular dynamics simulations of mixtures of sodium dodecyl sulfate (SDS) and 1-dodecanol molecules on a graphite surface were carried out at low and high concentration to investigate the formation of aggregates on the solid plate. The simulations showed that at low concentration the surfactants were well adsorbed on the surface by forming layers structures or a hemicylinder aggregate for a slightly higher surfactant concentration whereas at the highest concentration the surfactants formed monolayer-like structures localized away from the graphite surface with a water bin between the monolayer and the graphite plate. Therefore, we obtained different arrays of those observed in recent simulations of pure SDS adsorbed on graphite at the same concentration reported in the literature. The unexpected water layer between the 1-dodecanol and the graphite surface, at the highest concentration, was explained in terms of the Hamaker constants. The present results suggest that the formation of aggregates on solid surfaces is a combined effect not only of the surfactant–surfactant and the surfactant–wall interactions but also of the surfactant concentration.
Keywords: Computer simulations; Surfactant mixture; Surfactant structure; Solid surfaces;
Rearrangement of layered double hydroxide nanoplatelets during hollow colloidosome preparation by Guopeng Liu; Shangying Liu; Xiaoqiang Dong; Fei Yang; Dejun Sun (302-306).
Hollow colloidosome fabricated from emulsion droplet stabilized by LDH platelets. During preparation, the platelets changed their orientation from lying flat on the droplet surface to standing erect in the colloidosome shell.Hollow colloidosomes consisting of plate-like Mg/Al layered double hydroxide (LDH) nanoparticles have been prepared by a facile route from a Pickering emulsion. The particles are first adsorbed onto the surface of paraffin oil-in-water emulsion droplets. After the core oil is dissolved in the surrounding bulk liquid, using solvents that are miscible with both the internal and external phases of the droplets, colloidosomes are formed. In this process, we find that the diameters of the colloidosomes are significantly reduced compared to those of the emulsion droplets. The reduction in the diameter is caused by rearrangement of the LDH platelets. That is, the platelets change their orientation from lying flat on the emulsion droplet surface to standing erect in a dense, face-to-face connecting pattern in the colloidosome shell. The main reason for the particle rearrangement is the increase of the attractive forces among the particles due to the reduced polarity of the solvents used during colloidosome preparation.
Keywords: Colloidosomes; Pickering emulsion; Layered double hydroxide (LDH); Platelet; Rearrangement;
Tribology of steel/steel interaction in oil-in-water emulsion; a rationale for lubricity by Deepak Kumar; Jency Daniel; S.K. Biswas (307-315).
Small droplet of oil in an emulsion aids lubricity. The process of entrainment of droplet is explained by DLVO interaction and a lubrication model is proposed.Oil droplets are dispersed in water by an anionic surfactant to form an emulsion. The lubricity of this emulsion in steel/steel interaction is explored in a ball on flat nanotribometer. The droplet size and charge are measured using dynamic light scattering, while the substrate charge density is estimated using the pH titration method. These data are combined to calculate the DLVO forces for the droplets generated for a range of surfactant concentration and two oil to water volume ratios. The droplets have a clear bi-modal size distribution. The study shows that the smaller droplets which experience weak repulsion are situated (at the highest DLVO barrier) much closer to the substrate than the bigger droplets, which experience the same DLVO force, are. We suggest that the smaller droplets thus play a more important role in lubricity than what the bigger droplets do. The largest volume of such small droplets occurs in the 0.5 mM–1 mM range of surfactant concentration and 1% oil to water volume ratio, where the coefficient of friction is also observed to be the least.
Keywords: Anionic surfactant; Droplet size; DLVO; Emulsion; Friction; Interaction force;
Foaming properties of protein/pectin electrostatic complexes and foam structure at nanoscale by I. Schmidt; B. Novales; F. Boué; M.A.V. Axelos (316-324).
Location of species in a foam from a solution containing protein (green spheres) and pectin (blue lines). At air–water interface free proteins stabilize the film. In Plateau borders, complexes slow down drainage.The foaming properties, foaming capacity and foam stability, of soluble complexes of pectin and a globular protein, napin, have been investigated with a “Foamscan” apparatus. Complementary, we also used SANS with a recent method consisting in an analogy between the SANS by foams and the neutron reflectivity of films to measure in situ film thickness of foams.The effect of ionic strength, of protein concentration and of charge density of the pectin has been analysed. Whereas the foam stability is improved for samples containing soluble complexes, no effect has been noticed on the foam film thickness, which is almost around 315 Å whatever the samples. These results let us specify the role of each specie in the mixture: free proteins contribute to the foaming capacity, provided the initial free protein content in the bulk is sufficient to allow the foam formation, and soluble complexes slow down the drainage by their presence in the Plateau borders, which finally results in the stabilisation of foams.
Keywords: Pectin; Protein; Polyelectrolyte–protein complexes; Phase diagram; Surface tension; Complexes at interface; Foam; Foaming capacity; Foam stability; Thin liquid films; Small-angle neutron scattering (SANS); Neutron Reflectivity; Plateau border; Film;
Temperature-responsive polymer-brush constructed on a glass substrate by atom transfer radical polymerization by Hiromi Kitano; Takuya Kondo; Hisatomo Suzuki; Kohji Ohno (325-331).
Temperature-responsiveness of non-specific adsorption of various proteins to the surface-grafted polymer brush.A polymer brush of 2-(2-methoxyethoxy)ethyl methacrylate (MDM) was prepared by atom transfer radical polymerization (ATRP) using a 11-(2-bromoisobutyroyloxy)undecyl moiety-carrying initiator covalently fixed to a glass substrate. An aqueous solution of the MDM polymer (E-PMDM), which had been prepared for comparison, turned to be opaque above certain temperature (26.2 °C for E-PMDM (M n,GPC = 1.84 × 104)), which was corresponding to the lower critical solution temperature (LCST) of the polymer. The PMDM polymer brush accumulated on the glass surface also indicated temperature-responsive changes in contact angle of air bubble in the air-in-water system. Furthermore, non-specific adsorption of various proteins (bovine serum albumin (BSA), human immunoglobulin G (IgG) and bovine plasma fibrinogen (BPF)) to the surface of polymer brush on the glass plate was examined by the bicinchoninic acid method. The PMDM brush did not adsorb IgG and BPF significantly below the LCST of the polymer chain, whereas adsorbed a larger amount of the proteins above the LCST. A similar but less significant temperature-responsive adsorption was observed in the case of BSA. These results suggest usability of the temperature-responsive polymer-brushes with pendent ω-methoxy oligo(ethylene glycol) groups to coat various materials for bio-medical applications.
Keywords: Atom transfer radical polymerization; Lower critical solution temperature; Polymer-brush; Protein adsorption; Temperature-responsiveness;
Mechanism of PEO–PPO–PEO micellization in aqueous solutions studied by two-dimensional correlation FTIR spectroscopy by Lianwei Jia; Chen Guo; Liangrong Yang; Junfeng Xiang; Yalin Tang; Chunzhao Liu; Huizhou Liu (332-337).
New insight into the sequence of group associations in PEO–PPO–PEO copolymers was obtained during temperature-induced micellization, using 2D FITR spectroscopy.The micellization mechanism of PEO–PPO–PEO block copolymer in aqueous solutions was studied by two-dimensional correlation FTIR spectroscopy. The 1400–1000 cm−1 region was investigated, involving the stretching vibrations of ether band, C–H wagging vibrations of EO methylene groups and C–H symmetric deformation vibrations of PO methyl groups. In the 2D correlated spectra, the hydrous and anhydrous state of the ether band, PO methyl groups, and the two conformations of EO methylene groups were observed. Molecules with different PO lengths and increasing molecular weight were investigated to determine the sequence of association of the separate groups. During temperature-induced micellization, the following changes were detected: firstly, EO methylene groups changed from a gauche state to a trans state; secondly, conformational transitions led to the dehydration of hydrated methyl groups; next, the hydrogen bonding between C–O band and water diminished; and finally, dehydrated groups approached to form hydrophobic cores, resulting in micelle formation. From this variation in the sequence of group associations, it is concluded that aggregates of unimers first formed, then hydrophobic cores formed through the hydrophobic interaction from dehydrated PPO blocks, and proper micelles eventually evolved. The temperature-induced conformational changes are suggested the reason for micellization.
Keywords: Pluronic block copolymer; Micellization; 2D FTIR;
Proton magnetic relaxation and the aggregation of n-octylammonium n-octadecanoate surfactant in deuterochloroform solution by Michael A. Desando; Gojmir Lahajnar; Ana Sepe (338-345).
1H NMR spin–lattice ( T 1 ) and spin–spin ( T 2 ) relaxation times of n-octylammonium n-octadecanoate in CDCl3 show correlation to concentration and chemical shift (δ). Theoretical calculations using rotational diffusion and association equilibrium models are consistent with small reverse micelle formation. 1H NMR spin–lattice and spin–spin relaxation times of isotropic solutions of n-octylammonium n-octadecanoate in deuterochloroform containing ca. 0.1–0.2% tetramethylsilane (v/v) at ca. 292 K are observed to vary with position of the functional group in the amphiphile ion-pair, and with solute concentration. The latter dependence can be satisfactorily described using either single or multiple equilibria models of association complex formation of the reverse micelle type above a critical concentration (ca. 0.13 mol kg−1). Transverse relaxation is accounted for predominantly via reorientation/rotational diffusion of monomers and micellar aggregates, and is analyzed in terms of two component times, while longitudinal relaxation principally involves motions of different size segments around covalent bonds. Picosecond correlation times are attributed to intramolecular and monomer rotations, whereas multimer reorientation/tumbling processes are an order of magnitude longer. Results are analyzed for size of the reorienting species in terms of theoretical calculations for rotational diffusion of model cylindrical and ellipsoidal volumes of revolution, which above the critical micelle concentration correspond to association complexes of 2–4 monomers. Dilution shifts of the proton NMR peak positions also comply with the model of reverse micelle formation. The use of nonspinning liquid samples for the characterization of micellization phenomena via a nuclear magnetic resonance imaging spectrometer is investigated.
Keywords: 1H NMR spin relaxation; Surfactant aggregation; n-Octylammonium n-octadecanoate; Reverse micelle; Rotational diffusion;
The clouding behaviour of PEO–PPO based triblock copolymers in aqueous ionic surfactant solutions: A new approach for cloud point measurements by Tejas Patel; Pratap Bahadur; Jitendra Mata (346-350).
Schematic representations of Reverse Pluronic (PPO-PEO–PPO) and Pluronic (PEO–PPO–PEO) micelles in aqueous solutions.The cloud points (CP) of 1 g/dl solutions of polyethylene oxide–polypropylene oxide (PEO–PPO) based triblock copolymers (Pluronics® P84, L64, L44 and Reverse Pluronics® 10R5, 25R4, 17R4) were measured as a function of their molecular weight and added ionic surfactant. For identical PEO/PPO ratios, copolymers with lower molecular weight show a larger increase in the cloud point in the presence of surfactants than polymers with higher molecular weight. The opposite trend has been observed for reverse Pluronics. The cloud points of polymers with different PEO/PPO ratios have also been reported. An increase in the size of the middle PEO block in reverse Pluronics has a more significant effect on cloud points than molecular weight increment. Ionic surfactants produced marked increases in the cloud points of copolymer solutions. The effect was much larger for surfactants with higher hydrophobicity. Cationic surfactants with different chain lengths were used to examine the surfactant–polymer interaction. A novel approach for normalising the cloud points to their relative values has been carried out to see the clear effect of ionic surfactants. Tri component systems, comprising polymers, cetyltrimethylammonium bromide (C16TABr) surfactant and salt (NaBr), have also been studied to see the effect of salt on the phase separation behaviour of solutions within the framework of our new cloud point approach.
Keywords: Pluronics; Reverse Pluronics; Relative cloud points; Cationic surfactants; HLB value;
Effect of monomeric and polymeric co-solutes on cetyltrimethylammonium bromide wormlike micelles: Rheology, Cryo-TEM and Small-angle neutron scattering by Kelly R. Francisco; Marcelo A. da Silva; Edvaldo Sabadini; Göran Karlsson; Cécile A. Dreiss (351-359).
The addition of small amounts (20 mM) of monomeric and polymeric co-solutes to CTAB/NaSal wormlike micelles drastically reduces the viscoelasticity: benzyl alcohol (green); benzene (red); PPO (blue). Surprisingly however, no changes in the micellar microstructure are observed by SANS (inset).The effect of hydrophobic and hydrophilic co-solutes on the rheological properties of wormlike micelles of cetyltrimethylammonium bromide (CTAB) and sodium salicylate (NaSal) or sodium bromide (NaBr) was investigated. Monomeric (ethanol, 2-propanol, benzene and benzylic alcohol) and polymeric species (poly(ethylene oxide), poly(vinyl alcohol) and poly(propylene oxide), respectively PEO, PVA and PPO) of varying molecular weight were studied in order to assess the effect of co-solute ‘length’ on the interactions with the wormlike micelles. Rheological properties were characterised by the plateau modulus G 0 and the relaxation time τR obtained from fits to the Maxwell model, and by the zero-shear viscosity η 0. The rheological properties were unaltered by the addition of all hydrophilic solutes (up to 20 mM). With hydrophobic co-solutes instead, both η 0 and τR decreased considerably, while G 0 was unaffected. The effects were particularly remarkable with PPO for concentrations as low as 5 mM (ca. 0.3 g L−1), and τR was seen to follow an exponential decrease with polymer Mw . The effect of the aromatic solutes (benzene and benzyl alcohol) on the rheology was highly dependent on the counterions used to induce micellar growth (Sal− or Br−), revealing a different type of interaction. Surprisingly, small-angle neutron scattering and Cryo-TEM measurements showed that the drastic changes observed in the rheology were not correlated to any visible structural change. Therefore the strong decrease in viscosity and relaxation time are to be attributed to other mechanisms than micellar break-up or rod-to-sphere transition.
Keywords: Wormlike micelles; CTAB/NaSal; Additives; Viscoelastic properties; Phantom model;
A novel multi-responsive polyampholyte composite hydrogel with excellent mechanical strength and rapid shrinking rate by Kun Xu; Ying Tan; Qiang Chen; Huiyong An; Wenbo Li; Lisong Dong; Pixin Wang (360-368).
The composite hydrogels consist of cross-linked ungrafted polyampholyte chains as the first network and microgels with graft polyampholyte chains as graft points and second network and show surprising mechanical strength and rapid response rate. The investigation shows the compress strength of composite hydrogels is up to 17–30 MPa, which is 60–100 times higher than that of hydrogel matrix. The composite hydrogel shows reversible switch of transmittance without any volume change when traveling the lowest critical temperature (LCST) of microgels.Series of hydrophilic core–shell microgels with cross-linked poly(N-isopropylacrylamide) (PNIPAAm) as core and poly(vinyl amine) (PVAm) as shell are synthesized via surfactant-free emulsion polymerization. Then, the microgels are treated with a small amount of potassium persulfate (KPS) to generate free radicals on the amine nitrogens of PVAm, which subsequently initiate the graft copolymerization of acrylic acid (AA), acryloyloxyethyl trimethyl ammonium chloride (DAC), and acrylamide (AAm) onto microgels to prepare multi-responsive composite hydrogels. The composite hydrogels consist of cross-linked ungrafted polyampholyte chains as the first network and microgels with grafted polyampholyte chains as graft point and second network and show surprising mechanical strength and rapid response rate. The investigation shows the compress strength of composite hydrogels is up to 17–30 MPa, which is 60–100 times higher than that of the hydrogel matrix. The composite hydrogel shows reversible switch of transmittance when traveling the lowest critical temperature (LCST) of microgels. When the composite hydrogel swollen in pH 2.86 solution at ambient condition is immersed into the pH 7.00 solution at 45 °C, a rapid dynamic shrinking can be observed. And the character time (τ) of shrinking dynamic of composite hydrogel is 251.9 min, which is less than that of hydrogel matrix (τ = 2273.7 min).
Keywords: Polyampholyte; Composite hydrogels; Mechanical properties;
Exchange-dynamics of a neutral hydrophobic dye in micellar solutions studied by Fluorescence Correlation Spectroscopy by Jorge Bordello; Mercedes Novo; Wajih Al-Soufi (369-376).
Flickering of the fluorescence intensity reveals the fast exchange dynamics of a hydrophobic dye between micelles and the surrounding aqueous solution. Fluorescence Correlation Spectroscopy yields the entry and exit rate constants.The dynamics of the exchange of the moderately hydrophobic neutral dye Coumarine 152 between the aqueous phase and the phase formed by neutral Triton X-100 micelles is studied by Fluorescence Correlation Spectroscopy. The changes in the photophysical properties of the dye in presence of the micelles are discussed. The low quantum yield, the low saturation threshold and the necessary high energetic excitation of this dye requires a careful selection of the experimental conditions in order to obtain dynamic and diffusional properties with reasonable precision. It is shown that the contrast between the brightness of free and bound dye has a strong influence on the sensitivity of the FCS experiment. The entry rate constant of the dye to the micelles, k + = (0.8 ± 0.3) × 1010 M−1 s−1, is very near to the diffusion controlled limit. The high association equilibrium constant of K = (129 ± 3) × 103 M−1 is mainly determined by the low exit rate constant, k − = (0.6 ± 0.2) × 105 s−1.
Keywords: Fluorescence Correlation Spectroscopy; Micelles; Dye exchange dynamics; Supramolecular dynamics; Coumarines; Triton X-100;
Spontaneous growth of self-relief wrinkles in freely floating lipid-based nanomembranes, formed on a reactive bath of polyoxometalate aqueous solution by Karine Mougin; Laurent Vonna; Loic Vidal; Hamidou Haidara (377-383).
Freely-floating (lipid DDAB/polyoxometalate) nanomembranes produced by reactive wetting on aqueous foundations: a) plain membrane, b) spontaneously occurring relief wrinkles, shown here close to a residual dried droplet.Wetting and capillarity have appeared over the last decadesas potential tools for the guided actuation, self-assembly and nanostructuration, and most recently as powerful “tool-free” techniques of micro-, and nano-fabrication, in the field of nanotechnology. The present work deals with such a use of wetting, achieving for the first time the spontaneous growth of composite (lipid-capped polyoxometalate) nanomembranes, using the reactive spreading film formed by the droplets of a lipid solution, on an aqueous foundation hosting the polyoxometalate ions. Moreover, we show that the internal stress produced by the reactive wetting, and the resulting self-movements of the drop could be accumulated within the drying spreading film, driving the spontaneous occurrence of wrinkles, in the freely floating nanomembranes that are thus formed. Finally, we showed that gravity-driven scaling relations for buckling instabilities apply to these spontaneously occurring wrinkles, allowing the in situ characterization of the physical properties of the nanomembranes. This approach that allowed producing floating nanomembranes of “lipid-capped Keggin ions” that were collectable as freestanding nanosheets may constitute a potential route for the fabrication of a wide range of functional (copolymers/metal nanoparticles) nanocomposite membranes.
Keywords: DDAB solution; Polyoxometalate; Aqueous base; Interface reaction; DDAB/polyoxometalate complex; Floating nanomembrane; Wrinkling;
pH-dependent polyampholyte SDS interactions by Mabya Fechner; Sabine Kosmella; Joachim Koetz (384-391).
Cooperative and non-cooperative interactions between the polyampholyte PalH and SDS.Aqueous solutions of sodium dodecylsulfate (SDS) and poly(N,N′-diallyl-N,N′-dimethyl-alt-maleamic carboxylate) (PalH), a synthetic pH-tuneable polyelectrolyte (PEL), have been investigated by various techniques at different pH-values in absence and presence of NaCl. Potentiometric measurements using a surfactant-selective electrode indicate a quite complex interaction mechanism, which can be subdivided into different regions, where non-cooperative, electrostatic and cooperative hydrophobic interactions are of relevance. It was concluded, that in dependence on pH, conformational changes are responsible for the different interaction behavior in the NaCl-free system. Isothermal titration calorimetry (ITC) suggests that early stage hydrophobic binding is an exothermic process followed by electrostatic interactions, which are endothermic in nature and entropy driven. After NaCl addition the interaction mechanism becomes independent of pH due to a screening of (i) attractive interactions between the surfactant head groups and oppositely charged binding sites and (ii) repulsive forces between the surfactant head groups. Furthermore, the ITC investigations have revealed that after salt-addition surfactant micelles interact with the polymer instead of separated SDS molecules due to a depression of the CMC.
Keywords: Polyelectrolyte–surfactant interactions; SDS; Critical association concentration (CAC); Potentiometry; Surfactant-selective electrode; Isothermal titration calorimetry;
Organization of amphiphiles. Part XI: Physico-chemical aspects of mixed micellization involving normal conventional surfactant and a non-ionic gemini surfactant by Pramila K. Misra; Sagarika Panigrahi; Uma Dash; Asit Baran Mandal (392-401).
A synergistic interaction has been observed between a non-ionic gemini surfactant, BAM and conventional surfactants SDS, CTAB and TX-100. A model of interaction has been proposed.A systematic study on the behaviour of mixtures of p-phenylenediamine-tertiarybutyloxy-carbonyl-bis-glycamide (BAM) with ionic hexadecyl-trimethyl-ammonium bromide (CTAB), and sodium salt of dodecyl sulphate (SDS), and non-ionic surfactant (TritonX-100) in solution has been investigated through different physico-chemical measurements. The mixtures of BAM (0.0194 mM) with various amount of CTAB/SDS/TritonX-100 have been analyzed through absorbance, conductivity, surface tension and zeta potential measurements. The mixed system is found to be more surface active than the individual surfactants, the synergistic interaction being more prominent in system involving ionic surfactants compared to that of non-ionic surfactant. The mixed micellization behaviour is evidenced from the appearance/disappearance of the excimer of the fluorescent probe, maximum adsorption density at the interface, aggregation numbers of the surfactant mixtures and the surface charge of the conventional surfactants. A suitable interaction model, elucidating the organizational hierarchy of gemini-conventional surfactant at the micelle–water and air–water interface has been proposed.Display Omitted
Keywords: Gemini surfactant; Zeta potential; Micropolarity; Surface charge; Mixed interaction; Interfacial adsorption energies; Maximum adsorption density;
Adsorption equilibrium and kinetics of CO2, CH4, N2O, and NH3 on ordered mesoporous carbon by Dipendu Saha; Shuguang Deng (402-409).
Pore-size distribution of ordered mesoporous carbon.Ordered mesoporous carbon was synthesized by a self-assembly technique and characterized with TEM, Raman spectroscopy, and nitrogen adsorption/desorption for its physical and pore textural properties. The high BET specific surface area (798 m2/g), uniform mesopore-size distribution with a median pore size of 62.6 Å, and large pore volume (0.87 cm3/g) make the ordered mesoporous carbon an ideal adsorbent for gas separation and purification applications. Adsorption equilibrium and kinetics of carbon dioxide, methane, nitrous oxide, and ammonia on the ordered mesoporous carbon were measured at 298 K and gas pressures up to 800 Torr. The adsorption equilibrium capacities on the ordered mesoporous carbon at 298 K and 800 Torr for ammonia, carbon dioxide, nitrous oxide, and methane were found to be 6.39, 2.39, 1.5, and 0.53 mmol/g, respectively. Higher adsorption uptakes of methane (3.26 mmol/g at 100 bar) and carbon dioxide (2.21 mmol/g at 13 bar) were also observed at 298 K and elevated pressures. Langmuir, Freundlich, and Toth adsorption equilibrium models were used to correlate all the adsorption isotherms, and a simplified gas diffusion model was applied to analyze the adsorption kinetics data collected at 298 K and four different gas pressures up to 800 Torr.
Keywords: OMC; Self-assembly; Adsorption; Equilibrium; Kinetics; Carbon dioxide; Methane; Nitrous oxide; Ammonia;
On an isotherm thermodynamically consistent in Henry’s region for describing gas adsorption in microporous materials by Marc Pera-Titus (410-416).
Overcoming the intrinsic limitations of the Dubinin–Astakhov isotherm in Henry’s region at low pressures using a new thermodynamic isotherm formulation.The Dubinin–Astakhov and Dubinin–Radushkevich isotherms, originally formulated from the classical volume filling theory of micropores, constitute the most accepted models for describing gas adsorption in microporous materials. The most important weakness of these equations relies on the fact that they do not reduce to Henry’s law at low pressures, not providing therefore a proper characterization of adsorbents in the early stage of adsorption. In this paper, we propose a way out of this inherent problem using the thermodynamic isotherm developed in a previous study [J. Llorens, M. Pera-Titus, J. Colloid Interface Sci. 331 (2009) 302]. This isotherm allows the generation of a series of equations that make available a comprehensive description of gas adsorption for the whole set of relative pressures (including Henry’s region), also providing explicit information about energy heterogeneity of the adsorbent through the two characteristic m parameters of the thermodynamic isotherm (i.e., m 1 and m 2 ). The obtained isotherm converges into the Dubinin–Astakhov isotherm for relative pressures higher than 0.1, the characteristic α parameter of this isotherm being expressed as α = m 2 - 1 and the affinity coefficient ( β ) as a sole function of m 2 . An expression differing from the Dubinin–Astakhov isotherm has been obtained for describing Henry’s region, providing relevant information about confinement effects when applied to zeolites.
Keywords: Microporous; Gas adsorption; Energy heterogeneity; Thermodynamic isotherm; Hypergeometric function; Affinity coefficient;
Adsorption of modified dextrins to a hydrophobic surface: QCM-D studies, AFM imaging, and dynamic contact angle measurements by Iliana G. Sedeva; Renate Fetzer; Daniel Fornasiero; John Ralston; David A. Beattie (417-426).
The movement of the three-phase contact line for a bubble attaching to a hydrophobic solid surface is impeded by the adsorption of a soft deformable polymer layer.The adsorption of three dextrin-based polymers, regular wheat dextrin (Dextrin TY), phenyl succinate dextrin (PS Dextrin), and styrene oxide dextrin (SO Dextrin) on a model hydrophobic surface, consisting of a mixed alkanethiol layer on gold, has been characterized using the quartz crystal microbalance with dissipation monitoring (QCM-D). The three polymers exhibited varying affinities and capacity for adsorption on the hydrophobic substrate. Atomic force microscope (AFM) imaging of the polymer layers indicates that all three polymers fully cover the surface. The effect of the three polymers on the static contact angle of the surface was studied using captive bubble contact angle measurements. The three polymers were seen to reduce the receding contact angle by similar amounts (approximately 14°) in spite of having varying adsorbed amounts and differences in adsorbed layer water content. Although no differences were observed in the ability of the polymers to reduce the static contact angle, measurements of the dynamic contact angle between a rising air bubble and the polymer covered substrate yielded stark differences between the polymers, with one polymer (SO Dextrin) slowing the dewetting by an order of magnitude more than the other two polymers. The differences in dewetting behavior correlate with the adsorbed layer characteristics determined by QCM-D and AFM. The role of the dynamic and static contact angle in the performance of a polymer as depressant is discussed.
Keywords: Quartz crystal microbalance; Polymer adsorption; Dextrin; Self-assembled monolayer; Bubble–surface attachment; Dynamic contact angle;
Hydroxylapatite nanorods: An efficient and promising carrier for gene transfection by Guo-Jun Wu; Lin-Zhu Zhou; Ke-Wei Wang; Feng Chen; Ying Sun; You-Rong Duan; Ying-Jie Zhu; Hong-Chen Gu (427-432).
TEM micrographs of HAP nanorods which were synthesized with polymers template-based technique and showed high DNA adsorption capability in the presence of Ca2+.Calcium phosphate (CaP) has been used as the vector for gene transfection in the past three decades with the characteristics of excellent biocompatibility and biodegradability. However, clinical application of calcium phosphate is still not popular due to poor-controlling of DNA/CaP complex preparation and its low transfection efficiency. In this study, block copolymer (PLGA–mPEG) assisted synthesis of hydroxylapatite (HAP) nanorods and DNA post-adsorbing method for transfection in vitro have been reported. By hydrothermal treatment, HAP nanorods with relatively uniform sizes of ∼100 nm in length and ∼25 nm in diameter and high crystallinity were prepared, which were characterized by TEM, XRD and FTIR measurements. In the presence of Ca2+ (0.2 mol/L), HAP nanorods showed ultra-high DNA loading capacity, which was significantly enhanced by one or two magnitude compared with the recently reported high loading capacity mesoporous silica vectors. HAP nanorods, therefore, have a great potential as the gene vector to deliver DNA into the cells effectively and safely.
Keywords: HAP nanorod; DNA adsorption; Transfection; Gene delivery;
Characterization and photochemical and antibacterial properties of highly stable silver nanoparticles prepared on montmorillonite clay in n-hexanol by Hirokazu Miyoshi; Hideki Ohno; Keisuke Sakai; Naho Okamura; Hiroki Kourai (433-441).
This novel method of preparation on montmorillonite clay in n-hexanol was very effective for fabricating photoactive Ag NPs, which remained stable on the clay for 12 years, provided a reaction site for photoredox reactions and exhibited antibacterial behavior against E. coli.Ag nanoparticles (NPs) of approximately 2.5 ± 0.6 nm in size with high stability were prepared on montmorillonite clay in n-hexanol ([Ag NP/clay]). The aqueous suspensions of Ag NP/clay obtained were colored pale yellow to gray, and an intense yellow surface plasmon band was observed at approximately 397–422 nm at a [Ag+] concentration of 0.01–1 M. Fluorescence peaks of these Ag NP/clay suspensions, which were due to interband transitions of Ag NPs, were observed at approximately 447 nm upon excitation at approximately 341 nm. Photoinduced charge separation and electron accumulation in the presence of 2-propanol were observed in the Ag NPs on the clay. The photogenerated holes indicate a reaction with OH− because the generation of • OH radicals decreased in the presence of 2-propanol, as observed using a spin-trapping electron spin resonance (ESR) method. The amount of H2 produced depended on the amount of Ag NPs on the clay and the concentration of 2-propanol in the suspension. Antibacterial activity of Ag NPs on clay was also observed against Escherichia coli even after 12 years. This simple method of preparation in n-hexanol led to the successful formation of highly stable and photoactive Ag NPs on montmorillonite clay.
Keywords: Silver nanoparticle; Montmorillonite clay; Fluorescence; OH radical; Photoreduction of hydrogen; E. coli; Antibacterial effect;
Binding of dicamba to soluble and bound extracellular polymeric substances (EPS) from aerobic activated sludge: A fluorescence quenching study by Xiangliang Pan; Jing Liu; Daoyong Zhang; Xi Chen; Wenjuan Song; Fengchang Wu (442-447).
This study shows that both of the two types of EPS have strong binding capacity for dicamba, and SEPS generally have stronger binding capacity than BEPS. The protein-like substances in SEPS formed more stable complexes with dicamba than those in BEPS. Protein-like substances have stronger binding capacity for dicamba than humic-like substances.Binding of dicamba to soluble EPS (SEPS) and bound EPS (BEPS) from aerobic activated sludge was investigated using fluorescence spectroscopy. Two protein-like fluorescence peaks (peak A with Ex/Em = 225 nm/342–344 nm and peak B with Ex/Em = 275/340–344 nm) were identified in SEPS and BEPS. Humic-like fluorescence peak C (Ex/Em = 270–275 nm/450–460 nm) was only found in BEPS. Fluorescence of the peaks A and B for SEPS and peak A for BEPS were markedly quenched by dicamba at all temperatures whereas fluorescence of peaks B and C for BEPS was quenched only at 298 K. A dynamic process dominated the fluorescence quenching of peak A of both SEPS and BEPS. Fluorescence quenching of peak B and C was governed a static process. The effective quenching constants (log Ka ) were 4.725–5.293 for protein-like fluorophores of SEPS and 4.23–5.190 for protein-like fluorophores of BEPS, respectively. Log Ka for humic-like substances was 3.85. Generally, SEPS had greater binding capacity for dicamba than BEPS, and protein-like substances bound dicamba more strongly than humic-like substances. Binding of dicamba to SEPS and BEPS was spontaneous and exothermic. Electrostatic force and hydrophobic interaction forces play a crucial role in binding of dicamba to EPS.
Keywords: Activated sludge; Binding; Extracellular polymeric substances; Dicamba; Fluorescence quenching;
Effect of oxidation level of n +-type mesoporous silicon surface on the adsorption and the catalytic activity of Candida rugosa lipase by Andrea Salis; Francesca Cugia; Susanna Setzu; Guido Mula; Maura Monduzzi (448-453).
The oxidation level of porous silicon surface affects both the adsorption and the catalytic properties of Candida rugosa lipase.In this work, we present the synthesis and characterization of n +-type porous silicon (PSi) layers. Our final aim is the fabrication of a biosensor that exploits the semiconductive properties of this material. PSi wafers were used as a matrix for enzyme adsorption. These wafers, as a result of their porous nanostructure, had a high surface area (360 m2/g) and pore size in the range 5–20 nm. The freshly prepared PSi was stabilized through controlled anodic oxidation. Two classes of samples differing for the level of oxidation were prepared. The first class was oxidized up to 2 V (LO-PSi), whereas the second class was oxidized up to 10 V (HO-PSi). Both samples were used for the adsorption of Candida rugosa lipase. A significantly higher loading was ascertained for LO-PSi (140 mg/g) compared to HO-PSi (47 mg/g). The different hydrophobic–hydrophilic balance of the PSi surfaces induced by the different oxidation voltage affects the physical interactions that address the adsorption process of the lipase. The higher loading achieved with the LO-PSi resulted in a higher activity of the immobilized biocatalyst but in a lower catalytic efficiency. The two biocatalysts showed an acceptable stability toward storage (pH 5 buffer solution at 5 °C) within 2 weeks.
Keywords: Mesoporous silicon; Surface; Oxidation level; Lipase; Adsorption; Biosensor;
Functionalization of adsorbent with different aliphatic polyamines for heavy metal ion removal: Characteristics and performance by Changkun Liu; Renbi Bai; Liang Hong; Tao Liu (454-460).
Cu ion adsorbed on diethylenetriamine (DETA)-functionalized PGMA beads.This paper examines the characteristics of poly(glycidyl methacrylate) (PGMA) beads functionalized with different aliphatic polyamines as adsorbents and their performance in copper ion adsorption. The four aliphatic polyamines evaluated include ethylenediamine (EDA), diethylenetriamine (DETA), triethylenetetramine (TETA), and tetraethylenepentamine (TEPA). Various analytical tools, including elemental analysis, BET, and XAFS (XANES + EXAFS), were used to characterize the adsorbents in terms of their immobilized amine contents, polyamine densities, and their coordination structures for the adsorption of a typical heavy metal ion, Cu2+. It was found that the immobilized polyamine densities followed the order of EDA > DETA > TETA > TEPA, but the immobilized amine contents followed the opposite order of TEPA > TETA > DETA > EDA. XAFS analysis for the adsorbents after copper ion adsorption revealed that the average coordination number of copper ion with the nitrogen atoms (in the range between 3 and 4) followed the order of DETA < TETA < EDA < TEPA. Hence, the molecular length and structure of the polyamines appeared to have a great effect on the adsorption performance of the prepared adsorbents. The study leads to the conclusion that among the four aliphatic polyamines, DETA-functionalized PGMA adsorbent was the most efficient one for copper ion removal because of the relatively higher amine content and lower coordination number, easier regeneration, and shorter preparation time of the adsorbent. The results provide some useful information for future studies in the selection of polyamines for adsorbent functionalization.
Keywords: Polyamine; Heavy metal ion; Adsorption; Characteristics; PGMA; XAFS;
Adsorption mechanisms of metal cations from water on an oxidized carbon surface by C. Moreno-Castilla; M.A. Álvarez-Merino; L.M. Pastrana-Martínez; M.V. López-Ramón (461-466).
Acidity constant distributions at 288 K (▪) and 308 K (▪) of the surface oxygen groups of the oxidized activated carbon.Adsorption of Cr(III), Mn(II), Cu(II) and Zn(II) on an oxidized activated carbon cloth was studied. Its surface chemistry was characterized by potentiometric titration. This technique revealed the amount of surface oxygen functionalities and their acidity constant distribution. The acidity constant range involved in the metal cation adsorption was obtained from this distribution. Metal cation adsorption increased with higher adsorption temperature due to the increase in the negative surface charge of the oxidized activated carbon. Adsorption was by proton exchange and the number, amount and strength of the surface acid groups involved could be obtained. The proton exchange was by an inner-sphere or outer-sphere surface metal complex formation mechanism. In the case of divalent cation adsorption, the increase in temperature changed the adsorption mechanism from outer-sphere to inner-sphere. However, the adsorption mechanism of Cr(III) was outer-sphere and independent of temperature. Adsorption capacity augmented with the increase in the charge-to-size ratio of the hexa-aquo cations. In addition, the adsorption capacity of divalent cations increased with the rise in stability of the surface metal complex formed.
Keywords: Metal ion adsorption; Inner-sphere mechanism; Outer-sphere mechanism; Oxidized carbon surface;
Synthesis of nanometer-size Bi3TaO7 and its visible-light photocatalytic activity for the degradation of a 4BS dye by Gaoke Zhang; Ming Li; Shujie Yu; Shuiming Zhang; Baibiao Huang; Jiaguo Yu (467-473).
A novel nanometer Bi3TaO7 photocatalyst was synthesized by a facile and low-cost sol–gel method, which showed a strong adsorbability and a high visible-light photocatalytic activity for the degradation of 4BS.Most of tantalate photocatalysts are mainly synthesized by solid-state (SS) reaction methods and only show photocatalytic activity under UV light irradiation. Ta2O5 as a raw material shows an extremely high chemical stability, limiting its application to a few systems. A novel nanometer Bi3TaO7 photocatalyst was synthesized by a facile and low-cost sol–gel method using Ta2O5 and Bi(NO3)3·5H2O as the Ta and Bi sources, respectively. The as-obtained samples were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), UV–vis diffuse reflection spectroscopy (DRS) and Fourier transform infrared spectroscopy (FT-IR). The band gap energy of the as-obtained nanometer Bi3TaO7 photocatalyst was determined to be about 2.75–2.86 eV. The Bi3TaO7 nanopowders show a strong adsorbability and a high visible-light photocatalytic activity for the degradation of 4BS, which can be ascribed to the surface physicochemical properties and structure of the Bi3TaO7 nanometer catalyst. The degradation of 4BS is attributed to the photocatalysis but not to the adsorption of 4BS on the as-prepared catalyst.
Keywords: Bismuth; Tantalum; Nanosized Bi3TaO7; Visible-light; Photocatalytic; 4BS;
Influences of properties of protein and adsorption surface on removal kinetics of protein adsorbed on metal surface by H2O2-electrolysis treatment by Koreyoshi Imamura; Manabu Oshita; Masumi Iwai; Toshiki Kuroda; Ippei Watanabe; Takaharu Sakiyama; Kazuhiro Nakanishi (474-480).
Removal of adsorbed BSA from metal surface by H2O2-electrolysis: protein molecule, forming more adsorptive interaction with a metal surface, tends to show a lower removal rate.“H2O2-electrolysis” treatment is an alternative method for removing proteinaceous materials that are adsorbed to metal surfaces. The method is based on the generation of hydroxyl radicals by electrolysis of hydrogen peroxide and the subsequent decomposition of organic substances adhering to the metal surface. We herein investigated the influence of some parameters on the kinetics of protein removal by H2O2-electrolysis. These parameters included the properties of proteins and the type of metal surface. Sixteen types of proteins and nine types of metal surfaces were used. The removal of adsorbed protein from a metal surface during the treatment was monitored by ellipsometry. Apparent first-order rate constants for removal, kc l, for various adsorption and treatment conditions were determined. The kc l value varied markedly with the type of protein and was also influenced by the pH used in the adsorption. The isoelectric point (pI) of protein used was found to be a major factor. The amount of adsorbed protein removed by a unit amount of • OH was larger for a metal surface with a lower pI. The impact of the properties of the protein and metal surface on the removal kinetics are discussed, focusing on relationships with the adsorption characteristics of the protein.
Keywords: Hydroxyl radical; Proteinaceous soil; Radical oxidation; Electrolysis; Ellipsometry; Hydrogen peroxide; Metal surface;
Kinetic study of the adsorption of nitroimidazole antibiotics on activated carbons in aqueous phase by J.D. Méndez-Díaz; G. Prados-Joya; J. Rivera-Utrilla; R. Leyva-Ramos; M. Sánchez-Polo; M.A. Ferro-García; N.A. Medellín-Castillo (481-490).
Hydrophobic interactions govern the adsorption of nitroimidazoles on activated carbons. A model that combines external mass transport and intraparticle diffusion was applied, achieving an adequate fit to the experimental data.The adsorption kinetics of four nitroimidazoles, Dimetridazole (DMZ), Metronidazole (MNZ), Ronidazole (RNZ) and Tinidazole (TNZ), were studied on three activated carbons: two commercial carbons from Sorbo-Norit (S) and Merck (M) and a third prepared by chemical activation of petroleum coke (C). Experimental data of the corresponding adsorption kinetics were analyzed by applying pseudo-first and pseudo-second-order models and a general diffusion model. Application of pseudo-first and pseudo-second-order kinetic models verified the following: (i) The kinetic model used that better predicts the adsorption rates depends of both the adsorbent and adsorbate studied. (ii) Nitroimidazole adsorption rate decreases in the order MNZ > DMZ > RNZ > TNZ; therefore, in the case of MNZ, molecular size does not appear to be a determining factor in the process. (iii) Nitroimidazole adsorption rate on carbons increases in the order C < S < M, which is related to the increase in carbon hydrophobicity. Hence, in general, hydrophobic interactions appear to govern the kinetics of the adsorption process. Finally, a general diffusion model was applied that combines external mass transport and intraparticle diffusion, achieving an adequate fit to the experimental data. There are notable differences among the diffusivity values for the different nitroimidazoles that do not appear to be exclusively related to carbon textural parameters or adsorbate size. Therefore, adsorbent and adsorbate chemical characteristics are highly important to establish the adsorption mechanism of nitroimidazoles on activated carbons.
Keywords: Nitroimidazoles; Activated carbon; Adsorption kinetics; Intraparticle diffusion;
A novel multinozzle electrospinning process for preparing superhydrophobic PS films with controllable bead-on-string/microfiber morphology by Naiqian Zhan; Yaoxian Li; Chaoqun Zhang; Yan Song; Hengguo Wang; Lei Sun; Qingbiao Yang; Xia Hong (491-495).
This study demonstrates the fabrication of superhydrophobic polystyrene surfaces containing bead-on-string fibers and micro-sized fibers by multinozzle electrospinning. The relationship between CA value and mass ratio of bead-on-string fibers/micro-sized fibers, as well as the effect of micro-sized fibers to the mechanical property of electrospun mat is investigated.Superhydrophobic polystyrene (PS) surfaces with mechanical integrity were manufactured by electrospinning in this work. We first report a novel strategy here to combine bead-on-string fibers from 4% PS solution and micro-sized fibers from 20% PS solution homogeneously in one electrospinning step by multinozzle electrospinning. The superhydrophobicity of electrospun sheet can be achieved by the presence of bead-on-string fibers, while micro-sized PS fibers are responsible for the improvement of mechanical property of electrospun mat due to their elastic and flexible behavior. The distinctive design of our multinozzle electrospinning setup places two nozzles in separate electrical fields which guarantee that fibers with different structures are mixed homogeneously. We investigate the relationship between the mass ratio of fibers from two types of solutions and the CA of electrospun mat, the effect of mass ratio to the mechanical property of electrospun mat can also be observed. The result shows that CA value of PS surface merely comprised of bead-on-string fibers could reach up to 154.65°. As the content of microfibers increased, the value of CA decreased, ranging from 153.66° to 145.94°, but the tensile strength of composite mat was enhanced from 0.50 MPa to 1.22 MPa correspondingly which is beneficial to put the mats into practice.
Keywords: Multinozzle electrospinning; Superhydrophobic; Polystyrene;
Enhanced metal adsorption on solid suspensions by organic molecules by Galal Elmanfe; Ludovic Stephan; René Olier; Mireille Privat (496-504).
Pb2+ physical adsorption on silica is increased in presence of non-linked organics.This laboratory study mimicked the pollution of a suspension of silica beads, used as a crude model of sand, by naphthalene in mixture with carbofuran at first, and then by this mixture in association with a metal salt, Pb(NO3)2. The silica properties and the working conditions were such that they allowed us to only observe physisorption, which is the first and essential step of any adsorption mechanism. Naphthalene and carbofuran were, respectively, chosen as hydrocarbon and pesticide. Naphthalene adsorption from simple solutions is rather large compared to other organic adsorptions, and carbofuran seems to adsorb on a layer of naphthalene when the latter is mixed in solution with carbofuran. Like other organics, naphthalene favours the adsorption of lead ions, but ionic adsorption is considerably increased by the combination of naphthalene and carbofuran. The Wagner–Onsager–Samaras theory shows that the result implies a special organization of organic molecules at the interface. Conclusions about some environmental mechanisms of fixation, or release, of ions on sands in the case of simple physisorption are drawn from the study.
Keywords: Coadsorption; Organics; Salt; Wagner–Onsager–Samaras;
Interaction between like-charged particles at a liquid interface: Electrostatic repulsion vs. electrocapillary attraction by Krassimir D. Danov; Peter A. Kralchevsky (505-514).
Charged particles at a liquid interface experience a direct electric repulsion and an electrocapillary attraction. The derived asymptotic expressions indicate that the attraction is weaker than the repulsion.The electric field of charged particles, which are adsorbed at a liquid interface, induces interfacial deformations (capillary menisci). The overlap of such deformations gives rise to electrocapillary force of interaction between the particles. Our goal is to quantify this interaction on the basis of a force approach, which is different from the approaches (mostly based on energy calculations) used by other authors. The fact that the electric field of adsorbed particles has a dipolar asymptotics (due to the image-charge effect) is utilized to derive an analytical expression for the meniscus profile. The comparison of the calculated profile with experimental data indicates that the results based on the dipolar approximation agree excellently with the data, except some small deviations near the contact line. The effect of the interfacial deformation on the electrostatic pressure is also taken into account. The two-particle electrocapillary problem is solved in bipolar coordinates without using the superposition approximation. It turns out that for uniform distribution of the surface charges, the electrocapillary attraction is weaker than the electrostatic repulsion at interparticle distances at which the dipolar approximation is applicable, so that the net force is repulsive. This result is in agreement with the conclusions of other authors obtained by using different theoretical approaches and with available experimental data. The analytical expressions for the electrocapillary and electrodipping forces derived in the present article provide a simple and convenient way for estimation of these forces.
Keywords: Particles at a liquid interface; Electrocapillary attraction; Electrodipping force;
A spectroscopic and photochemical study of Ag+-, Cu2+-, Hg2+-, and Bi3+-doped Cd x Zn1− x S nanoparticles by Volodymyr M. Dzhagan; Oleksandr L. Stroyuk; Oleksandra E. Rayevska; Stepan Ya. Kuchmiy; Mykhailo Ya. Valakh; Yuriy M. Azhniuk; Cristian von Borczyskowski; Dietrich R.T. Zahn (515-523).
Doping of colloidal Cd x Zn1− x S nanoparticles with Ag+, Cu2+, Hg2+, or Bi3+ was studied by a combination of absorption and photoluminescence spectroscopy with flash and steady-state and time-resolved photolysis techniques.A combination of stationary and time-resolved absorption and photoluminescence spectroscopy with flash and steady-state photolysis of Ag+, Cu2+, Hg2+, or Bi3+-doped Cd x Zn1− x S nanoparticles was used to assess the nature of the doping influence upon the optical properties of Cd x Zn1− x S nanoparticles. The relationships between the type and the concentration of a dopant and the dynamics of the photoinduced processes in the doped nanoparticles are derived and discussed.A correlation is found between the magnitude of doping-induced changes in the intensity and decay dynamics of the deep trap photoluminescence and an enhancement of the transient bleaching recovery and acceleration of the photocorrosive degradation of the doped Cd x Zn1− x S NPs compared to the undoped ones. The impact of the dopant upon the intensity of the luminescence and microsecond transient bleaching bands was found to grow substantially from Ag+ to Cu2+, Hg2+ and Bi3+. The same trend was found to hold for the acceleration of the steady-state photochemical corrosion of doped Cd x Zn1− x S nanoparticles. The differences among the effect of the dopant ions studied were interpreted in terms of the depth and charge of surface states created by Cd2+ (Zn2+) substitution by a dopant.
Keywords: Colloidal semiconductors; CdZnS nanoparticles; Doping; Photoluminescence; Pulse photolysis; Photocorrosion; Raman spectroscopy;
Molecular orientation and film structure of gramicidin on highly oriented pyrolitic graphite by Shuchen Hsieh; Wei-Jay Chao; Chiung-Wen Hsieh (524-527).
Gramicidin molecules deposited on HOPG surfaces switched from a flat-lying to upright orientation with increased surface coverage, and formed circular holes in the films.Gramicidin molecules were deposited on HOPG surfaces to characterize molecular orientation and film structure as a function of surface coverage and temperature. At low coverage (0.35 ML), the molecules adopted a flat-lying orientation and formed dendritic islands. At higher coverage (0.86 ML), molecules adopted an upright orientation and circular holes formed in the films. The upright film exhibited higher adhesion in force spectroscopy measurements, supporting our molecular orientation assignments. At elevated deposition temperatures (50 °C) on the higher coverage films, the holes were still present, but partially filled in. At 60 °C the film structure was quite different, forming tall irregular islands without the circular holes observed at lower temperatures. These results demonstrate that gramicidin molecular orientation and film structure on HOPG can be controlled by tuning the surface coverage and deposition temperature.
Keywords: Gramicidin; HOPG; Molecular orientation; Atomic force microscopy;
A new modified parachor model for predicting surface compositions of binary liquid mixtures. On the importance of surface volume representation by Martin Tjahjono; Marc Garland (528-537).
A new modified parachor model involving a more “realistic” surface volume representation is developed to provide prediction for the surface compositions on the air-binary liquid interface.Differences in composition between the surface region and the bulk region for binary liquids can occur due to preferential adsorption, and such surface enrichment can influence mass and heat transport across the interface. In order to investigate surface enrichment, reliable methods for predicting surface compositions are required. In this study, an approach based on a modified parachor model is developed in order to provide a generally more accurate prediction for the surface composition. In contrast to other predictive models, a more “realistic” surface volume representation is considered. This model is subsequently utilized to predict the surface compositions of several binary systems, involving organic–aqueous, organic–organic and aneotropic mixtures. The surface compositions obtained are compared to those directly determined from experimental measurements, if any, and to those calculated using other predictive models. The results show that the present modified parachor model provides surface composition predictions which are equal to, and in some cases are better than (particularly for aneotropic mixtures), those provided by other models. In general, the results demonstrate the usefulness of including a “real” surface volume approximation in the surface enrichment calculations.
Keywords: Surface enrichment; Surface tension; Density; Aneotropic mixture; Parachor;
Electroviscous effect of concentrated suspensions in salt-free media: Water dissociation and CO2 influence by Emilio Ruiz-Reina; Félix Carrique (538-546).
Electroviscous coefficient p against volume fraction ϕ: Only added counterions (dash, pure salt-free) and water dissociation and CO2 contamination ions (solid, realistic salt-free).The electroviscous effect of realistic salt-free colloidal suspensions is analyzed theoretically. We study the influence on the electroviscous coefficient of the surface charge density and the particle volume fraction. By realistic salt-free colloidal suspensions we mean aqueous suspensions which have been deionized as far as possible without any electrolyte added during the preparation, in which the only ions present can be (i) the so-called added counterions, coming from the ionization of surface groups and thus counterbalancing the surface charge, (ii) the H+ and OH− ions from water dissociation, and (iii) the ions produced by the atmospheric CO2 contamination. Our model is elaborated in the framework of a classical mean-field theory, using the spherical cell model approach and the appropriate local equilibrium reactions. It is valid for arbitrary surface charge density and particle concentrations. We have also made a new interpretation of the electroviscous coefficient: the electroviscous coefficient p of the suspension is the ratio between the electrohydrodynamic and the pure hydrodynamic contributions to the specific viscosity of the suspension. The numerical results show that it is necessary to consider the water dissociation influence for volume fractions lower than approximately 10−3, whereas the atmospheric contamination, if the suspensions are open to the atmosphere, is important in the region of volume fractions ϕ < 0.03.
Keywords: Colloids; Electroviscous effect; Suspension viscosity; Water dissociation; Atmospheric contamination;
Seismoelectric effect: A non-isochoric streaming current. 1. Experiment by Andrei S. Dukhin; Philip J. Goetz; Matthias Thommes (547-553).
Propagation of ultrasound through a porous body saturated with liquid generates an electric response, which is called “seismoelectric current”. It can be described as “streaming current” at non-isochoric conditions when compressibility becomes important. Seismoelectric currents can be measured with electroacoustic devices originally designed for characterizing liquid dispersions. This effect can be used for characterizing zeta potential, porosity and pore size of porous bodies.Propagation of ultrasound through a porous body saturated with liquid generates an electric response. This electroacoustic effect is called the “seismoelectric current”; the reverse process, when an electric field is the driving force, is called the “electroseismic current.” Seismoelectric currents can be measured with electroacoustic devices originally designed for characterizing liquid dispersions. Such electroacoustic devices must first be calibrated with a liquid dispersion and then used to characterize a porous body. We demonstrated such measurements of the seismoelectric current with electroacoustic devices in three different types of porous bodies. The first porous body was a deposit of solid submicrometer particles. We monitored the kinetics of the deposit formation on the surface of the electroacoustic probe. It allowed us to unambiguously confirm that the measured signal was generated by the deposit. We were also able to extract information about the porosity of the forming deposits. The second type of porous body was again a deposit, but instead of solid submicrometer particles, we used very large, porous glass spheres. According to classical theory, these glass particles are not supposed to generate any electroacoustic signal because colloid vibration current decays with increasing particle size due to the particles inertia. Nevertheless, we measured a strong signal, which was apparently associated with the pores of the particles. We were able to derive some conclusions about the dependence of the seismoelectric current on the pore size. The last tests were performed with cylindrical sandstone cores. These porous bodies have a very high hydrodynamic resistance that prevents measurement of the classical streaming current. We are able to measure a strong seismoelectric current that correlates with porosity of the cores.
Keywords: Steaming current; Seismoelectric current; Electroacoustics; Zeta potential; Porosity; Pore size; Porous body;
Comment on “Universal yield stress equation for transient response of zeolite based electrorheological fluid” by B.J. Park; H.J. Choi (554-555).
Using a critical electric field in the ER system and the universal yield stress equation, the reported experimental data was collapsed onto a single curve very well.We comment on the transient process of an electrorheological (ER) fluid under square-wave electric field excitation by analyzing its electric field-induced stable shear stress at a different shear rate. Using a critical electric field in the ER system, we find that the universal yield stress equation collapses the reported experimental data onto a single curve very well.
Keywords: Electrorheological fluid; Yield stress; Shear stress;
The influence of dicarboxylic acid structure on the stability of colloidal hematite by John J. Lenhart; Rachel Heyler; Eric M. Walton; Steven E. Mylon (556-560).
The structural orientation of the adsorbed acid at the hematite surface, not the adsorption mechanism, most strongly influences the stability of hematite nanoparticles.Low molecular weight organic acids comprise an important pool of reactive ligands in aquatic systems. These acids readily bind to nano-sized mineral particles and thereby strongly influence a particle’s physicochemical behavior. Predicting this influence requires the integration of molecular-level details that control surface complexation mechanisms and structures with macro-scale observations of mineral colloid behavior. We report on the aggregation kinetics of nano-sized hematite in the presence of fumaric acid and maleic acid, which are naturally occurring dicarboxylic acids of similar size and structure. Our results indicate that the structure and orientation of the adsorbed dianion at the hematite surface, not the adsorption mechanism, defines the resulting effect. Maleate, which directs both carboxyl groups to the surface in the form of inner- and outer-sphere surface complexes, enhances colloidal stability. Fumarate, however, which binds to the hematite surface as an outer-sphere complex with just one carboxyl group only slightly influenced particle stability. This outcome suggests that subtle differences in the structure of adsorbed acids produce important differences in the physicochemical behavior of particles in dilute aquatic systems.
Keywords: Surface complexation mechanism; Colloid aggregation; Steric interactions;
Reactivity and fusion between cationic vesicles and fatty acid anionic vesicles by Filippo Caschera; Pasquale Stano; Pier Luigi Luisi (561-565).
The spontaneous fusion between cationic vesicles and fatty acid vesicles has been revealed by assessing the mixing of their aqueous contents. Vesicle fusion can provide an useful “origin of life” model.The fusion between synthetic vesicles is an interesting mechanism for the stepwise construction of vesicle compartments for origins of life models and synthetic biology. In this communication, we report an innovative study on the not well-known case of fusion between oppositely charged vesicles, in particular by using fatty acid vesicles and DDAB as cationic surfactant. By combining fluorescence, turbidity vs. time profiles and vesicle size distribution obtained by dynamic light scattering, we show that POPC/oleate 1/4 mol/mol anionic vesicles can be fused with POPC/DDAB 1/1 mol/mol cationic vesicles with about 20% yield. Other non-fusion processes also occur, vesicle fusion being more effective by reducing the ionic strength of the buffer. This study also contributes to clarify the term “vesicle fusion”, which is not always properly used in describing reactivity among vesicles.
Keywords: Fatty acids; Symbiogenesis; DDAB; Vesicle fusion; Minimal cell; Origins of life;
Analysis of creaming and formation of foam layer in aerated liquid by Ganesan Narsimhan (566-572).
Creaming and formation of foam layer in aerated liquid is analyzed by coupling hindered creaming and foam syneresis to describe the compressibility of foam layer in terms of its structure.A model for creaming and formation of a foam layer in an aerated system consisting of Newtonian liquid is proposed. The variation of air volume fraction in the dispersion layer is described by hindered creaming which is coupled to syneresis in the top foam layer that is described by flow of liquid through a network of Plateau borders due to gravitational and capillary forces. The present analysis accounts for the compressibility of foam layer by coupling creaming analysis with syneresis in the foam layer. The behavior of the system is described by three parameters: (a) characteristic time scale of creaming of an isolated bubble, (b) hydrodynamic interaction factor, and (c) capillary number, ratio of capillary and gravitational forces in the foam layer. System behavior is shown to be different for four different regions of initial air volume fractions for which the phase diagram and evolution of the profile of air volume fraction for batch dispersion are presented.
Keywords: Creaming; Foam layer; Syneresis; Phase diagram; Volume fraction profile; Bubbles; Air–liquid dispersion;