Journal of Colloid And Interface Science (v.360, #1)
Cover 1 (OFC).
Extension of size of monodisperse silica nanospheres and their well-ordered assembly by Ryota Watanabe; Toshiyuki Yokoi; Erina Kobayashi; Yuki Otsuka; Atsushi Shimojima; Tatsuya Okubo; Takashi Tatsumi (1-7).
We have newly developed a liquid-phase method for preparing uniform-sized silica nanospheres (SNSs) 12 nm in size and their three-dimensionally ordered arrangement upon solvent evaporation. In this manuscript, the successful control of the sphere sizes in the range from 14 to 550 nm by the seed regrowth method is reported.Display Omitted► Successful control of the sphere sizes in the range from 14 to 550 nm by the seed regrowth method. ► Formation of porous material having 3D interparticle voids 3–130 nm in size. ► Preparation of three-dimensionally interconnected ordered porous carbons.A liquid-phase method for preparing uniform-sized silica nanospheres (SNSs) 12 nm in size and their three-dimensionally ordered arrangement upon solvent evaporation have recently been pioneered by us. Here we report the successful control of the sphere sizes in the wide range from 14 to 550 nm by the seed regrowth method. In this method, the dispersion of SNSs 14 nm in size as seeds was prepared in the emulsion system containing Si(OEt)4 (TEOS), water and arginine under weakly basic conditions (pH 9–10). An appropriate portion of this dispersion is added to the solution containing water, ethanol and arginine, and then TEOS is added. The additional TEOS introduced into the regrowth system contributed only to the resumed growth of the seeds, not to the formation of new silica particles. The size of interparticle pores was finely tuned by changing the size of the spheres. The preparation of three-dimensionally ordered porous carbons by using the colloidal array of silica nanospheres as a template is also reported.
Keywords: Silica nanospheres; Seed regrowth method; Basic amino acids;
Assembly of nanoparticles at the contact line of a drying droplet under the influence of a dipped tip by Kemal Keseroğlu; Mustafa Çulha (8-14).
A tip dipped into a drying droplet alters the behavior of contact line pinning. The chemistry of tip and surfaces the droplet placed has dramatic influence on concentric ring formation.Display Omitted► Assembly of nanoparticles can be controlled by manipulating the contact line pinning. ► Dipping a tip into drying droplet alters the behavior of nanoparticles. ► Tip surface chemistry influences the assembly of nanoparticles in the droplet. ► Different concentric ring formation mechanisms for hydrophilic and hydrophobic tips.The manipulation of colloidal nanoparticles (NPs) in a drying droplet has critical importance not only for several industrial applications but also their assembly into patterns on surfaces. The influence of a tip with hydrophilic or hydrophobic surfaces dipped into a drying droplet on hydrophilic or hydrophobic surfaces on the behavior of 98 nm latex NPs was investigated. The formation of concentric rings on hydrophilic glass surfaces regardless of the surface chemistry of the dipped tip was observed. On the other hand, no pattern formation on hydrophobic surfaces was observed with the insertion of the tip. With a hydrophilic tip, the concentric rings were formed due to stick–slip motion of the solvent contact line resulting from competition between pinning and capillary forces while the capillary effect was not effective until the surface of the tip was changed by adherent NPs making the tip surface available for water adherence with a hydrophobic tip, which results in the pulling of droplet towards the tip. It is also found that the tip thickness and suspension concentration significantly influences the formation of concentric rings on surfaces. This simple procedure can be used to influence the distribution or assembly of NPs in the droplet area.
Keywords: Nanoparticles; Droplet; Contact line pinning; Self-assembly;
Tuning the self-assembled monolayer formation on nanoparticle surfaces with different curvatures: Investigations on spherical silica particles and plane-crystal-shaped zirconia particles by Bernhard Feichtenschlager; Christoph J. Lomoschitz; Guido Kickelbick (15-25).
Amorphous spherical silica and plane-crystal-shaped zirconia particles were prepared and functionalized with long alkyl chain coupling agents. The effect of the nanoscopic curvature and the co-functionalization with a second coupling agent was investigated.Display Omitted► Alkyl-chain ordering on curved and plane nanoscopic surfaces. ► Disturbing self-assembled monolayer formation on nanoparticles by co-functionalization. ► Improvement of the dispersion behavior of nanoparticles by co-functionalization of their surface.The ordering of dodecyl-chain self-assembled monolayers (SAM) on different nanoscopic surfaces was investigated by FT-IR studies. As model systems plane-crystal-shaped ZrO2 nanoparticles and spherical SiO2 nanoparticles were examined. The type of capping agent was chosen dependent on the substrate, therefore dodecylphosphonic acid and octadecylphosphonic acid were used for ZrO2 and dodecyltrimethoxysilane for SiO2 samples. The plane ZrO2 nanocrystals yielded more ordered alkyl-chain structures whereas spherical SiO2 nanoparticles showed significantly lower alkyl-chain ordering. Submicron-sized silica spheres revealed a significantly higher alkyl chain ordering, comparable to an analogously prepared SAM on a non-curved plane oxidized Si-wafer. In the case of ZrO2 nanocrystals an intense alkyl-chain alignment could be disturbed by decreasing the grafting density from the maximum of 2.1 molecules/nm2 through the variation of coupling agent concentration to lower values. Furthermore, the co-adsorption of a different coupling agent, such as phenylphosphonic acid for ZrO2 and phenyltrimethoxysilane for SiO2, resulted in a significantly lower alkyl-chain ordering for ZrO2 plane crystals and for large SiO2 spherical particles at high grafting density. An increasing amount of order-disturbing molecules leads to a gradual decrease in alkyl-chain alignment on the surface of the inorganic nanoparticles. In the case of the ZrO2 nanoparticle system it is shown via dynamic light scattering (DLS) that the mixed monolayer formation on the particle surface impacts the dispersion quality in organic solvents such as n-hexane.
Keywords: Nanoparticles; Surface-functionalization; Self-assembled monolayers; Silica; Zirconia; Mixed monolayers;
Study of spectral behaviour and optical properties of cis/trans-bis(N-methylpyridinium-4-yl)diphenyl porphyrin adsorbed on layered silicates by A. Čeklovský; S. Takagi; J. Bujdák (26-30).
Proposed arrangement of head-to-tail assemblies (J-type) formed by trans-DPyP on the clay surface. Arrows indicate the transition dipole moments.Display Omitted► Spectral behaviour of two porphyrins upon adsorption on clays was investigated. ► Impact was given on layer charge influence on the visible and fluorescence spectra. ► Adsorption of porphyrins led to spectral changes but preserved their photoactivity. ► Observed effects are attributed to “flattening” of the porphyrins and aggregation.The spectral properties of two dicationic porphyrins, cis- and trans-bis(N-methylpyridinium-4-yl)diphenyl porphyrins, upon adsorption on clay mineral templates were investigated. A series of reduced charge Nanocor montmorillonites was used as host templates. The main impact was given on the influence of the layer charge on the absorption and fluorescence spectra. Adsorption of the porphyrins led to significant changes in their spectra but preserved the photoactivity of the dyes. The changes can be attributed to two phenomena: structural changes (flattening) of the porphyrin molecules and molecular aggregation. Latter one was more influenced by the molecular structure of the dyes and influenced the properties of mainly trans-isomer. The formation of the assemblies was significantly influenced by the layer charge of montmorillonite template. This study presents the example how one is able to influence the spectral properties and possibly also the functionality of adsorbed photoactive molecules via a strategy of appropriate combination of a photoactive component with specific inorganic templates.
Keywords: Porphyrin; Clay; Layer charge; Visible spectroscopy; Fluorescence spectroscopy; Molecular aggregation;
Manipulating interactions between functional colloidal particles and polyethylene surfaces using interfacial engineering by Khalid Ziani; Jeffrey A. Barish; David Julian McClements; Julie M. Goddard (31-38).
Interfacial interactions between droplets and modified polyethylene. In contrast to negatively charged droplets (A and C), positively charged droplets (B) absorb strongly to the anionic UV–ozone treated PE, which is attributed to electrostatic attraction.Display Omitted► Interactions between lipid droplets and polymer surfaces are investigated, considering effects of surface electrical charges. ► Polymer surfaces subjected to UV–ozone treatment are anionic, as determined by electrostatic dye interactions. ► Cationic droplets adsorb most strongly to UV–ozone treated materials, which is attributed to electrostatic attraction. ► Non-ionic and anionic droplets have weak or minimal interaction with non-ionic and anionic polymer surfaces. ► Results of this work are important in understanding the behavior of encapsulated lipophilic components in packaged foods and consumer products.The purpose of this study was to examine the interaction between lipid droplets and polyethylene surfaces, representative of those commonly used in food packaging. Lipid droplets with various surface charges were prepared by homogenizing corn oil and water in the presence of surfactants with different electrical characteristics: non-ionic (Tween 80, T80), cationic (lauric arginate, LAE), and/or anionic (sodium dodecyl sulfate, SDS). The ionic properties of polyethylene surfaces were modified by UV-treatment. Stable emulsions containing small droplets (d < 200 nm) with nearly neutral (T80), cationic (T80: LAE), and anionic (T80: SDS) charges were prepared by adding different levels of the ionic surfactants to Tween 80 stabilized emulsions. Scanning electronic microscopy (SEM), confocal fluorescence microscopy, and ATR-FTIR showed that the number of droplets attached to the polyethylene surfaces depended on the droplet charge and the polyethylene surface characteristics. The greatest degree of droplet adsorption was observed for the cationic droplets to the UV–ozone treated polyethylene surfaces, which was attributed to electrostatic attraction. These results are important for understanding the behavior of encapsulated lipophilic components in food containers.
Keywords: Emulsion; Stability; Surfactant; Polymer surface modification; Interactions; Packaging;
Curcumin-loaded biocompatible thermoresponsive polymeric nanoparticles for cancer drug delivery by N. Sanoj Rejinold; M. Muthunarayanan; V.V. Divyarani; P.R. Sreerekha; K.P. Chennazhi; S.V. Nair; H. Tamura; R. Jayakumar (39-51).
A nanoformulation for curcumin was investigated with the thermosensitive chitosan-g-PNVCL. The effects of these nanoformulation on normal as well as cancer cells were studied.Display Omitted► We developed curcumin-loaded chitosan-g-PNVCL nanoparticles for cancer therapy. ► This polymeric system is having biodegradable, biocompatible, and thermo-responsive property. ► This is highly efficient on cancer cells with minimal toxicity to normal cells in vitro. This study aims at the formulation of curcumin with biodegradable thermoresponsive chitosan-g-poly (N-vinylcaprolactam) nanoparticles (TRC-NPs) for cancer drug delivery. The spherical curcumin-loaded nanoparticles of size 220 nm were characterized, and the biological properties were studied using flow cytometry and cytotoxicity by MTT assay. The in vitro drug release was higher at above LCST compared to that at below LCST. TRC-NPs in the concentration range of 100–1000 μg/mL were non-toxic to an array of cell lines. The cellular localization of the curcumin-loaded TRC-NPs was confirmed from green fluorescence inside the cells. The time-dependent curcumin uptake by the cells was quantified by UV spectrophotometer. Curcumin-loaded TRC-NPs showed specific toxicity to cancer cells at above their LCST. Flow cytometric analysis showed increased apoptosis on PC3 compared to L929 by curcumin-loaded TRC-NPs. These results indicate that novel curcumin-loaded TRC-NPs could be a promising candidate for cancer drug delivery.
Keywords: Chitosan; Thermoresponsive nanoparticles; LCST; Curcumin; Specific toxicity; Cancer drug delivery;
An atomic force microscopy investigation on self-assembled peptide nucleic acid structures on gold(111) surface by S. Ghosh; R. Mukhopadhyay (52-60).
Molecularly resolved AFM image of PNA SAM on gold(111); A single PNA molecule is highlighted by black dotted circle; 1-dimensional molecular ordering and 2-dimensional inter-ribbon ordering is evident in the cross-section profiles.Display Omitted► Formation of self-assembled peptide nucleic acid structures on gold(111). ► Molecularly-resolved Atomic Force Microscopy images reveal 1-D as well as 2-D ordering. ► PNA concentration, incubation time, temperature and deposition method as controlling factors.Peptide Nucleic Acid (PNA) is an important alternative nucleic acid, which exhibits more effective DNA/RNA detection capabilities compared to DNA. Its potential utility in nucleic acid based detection technologies warrants detail understanding of it’s self-assembly behavior on solid substrates, e.g., gold. In the present study, we have applied high-resolution Atomic Force Microscopy (AFM) for obtaining direct visual information on PNA adsorption and formation of a self-assembled monolayer of PNA on gold(111) surface. We show from the molecularly resolved AFM data that PNA molecules form a well-defined 1-dimensional molecule-by-molecule ordering, over a considerable length scale (few hundred nm), as well as 2-dimensional ordering over a wide area of about 10 μm × 10 μm, due to parallel positioning of the 1-dimensional ordered arrangements. The way the parameters like PNA concentration, incubation time, incubation temperature and PNA deposition methods can affect the formation of such ordered self-assembled PNA structures has been investigated. Some of the primary observations are that the minimum PNA concentration and incubation time for large scale (10 μm × 10 μm) 2-dimensional order formation are 0.5 μM and 4 h, respectively. Furthermore, a dense and well-ordered layer over a large area could be better formed in case of immersion method compared to the droplet contact and droplet deposition methods. From the Reflection Absorption Infra Red Spectroscopy (RAIRS) data, indications for PNA concentration-driven reorientation of the PNA backbone towards more upright configuration on gold(111) surface, were obtained.
Keywords: Peptide Nucleic Acid; PNA; Self-assembly; Gold(111); Atomic Force Microscopy; AFM;
Temperature responsive flocculation and solid–liquid separations with charged random copolymers of poly(N-isopropyl acrylamide) by John-Paul O’Shea; Greg G. Qiao; George V. Franks (61-70).
Neutral PNIPAM produces dispersion at 25 °C and flocculation after heating to 50 °C. Counter-ionic PNIPAM produced flocculation at both 25 °C and after heating to 50 °C. Co-ionic PNIPAM produces dispersion both above and below the polymer LCST.Display Omitted► Comprehensive investigation of selective temperature responsive flocculation with charged random co-polymers of PNIAPM covering both sedimentation and secondary consolidation. ► Temperature influences settling and consolidation less with charged co-polymers which also act as conventional flocculants compared to neutral PNIPAM. ► Secondary consolidation is reduced with random charged co-polymers of PNIPAM compared to neutral PNIPAM even after the temperature is reduced to below the LCST.Temperature-responsive random copolymers based on poly(N-isopropyl acrylamide) (PNIPAM) with 15 mol% of either acrylic acid or dimethylaminoethyl acrylate quaternary chloride were prepared. The effect of the charge and its sign were investigated in the solid–liquid separation of silica and alumina mineral suspensions. The results were compared to PNIPAM homopolymer of similar molecular weight. PNIPAM copolymers of the same charge as the particles (co-ionic PNIPAM) act as dispersants at both 25 °C and 50 °C. Flocculation occurs when counter-ionic PNIPAM facilitates selective aggregation and rapid sedimentation of minerals at both 25 °C and 50 °C. Adsorption and desorption studies showed that, unlike non-ionic PNIPAM, little desorption of the counter-ionic copolymers from the oxides occurred after cooling a suspension from 50 °C to below the lower critical solution temperature. Thus, incorporation of counter-ionic charge into the temperature sensitive polymer PNIPAM was found to reduce the sediment bed consolidation upon cooling when compared to PNIPAM homopolymers. The lack of secondary consolidation upon cooling is attributed to attractive inter-particle forces, such as conventional polyelectrolyte flocculation mechanisms (bridging, charge neutralization or charge patch) which persist at both 25 °C and 50 °C when counter-ionic PNIPAM is used. On the other hand, it was possible to obtain rapid sedimentation with the counter-ionic PNIAPMs even when they were added to the suspension already at 50 °C, a process which has not been possible with neutral PNIPAM homopolymers.
Keywords: Poly(N-isopropyl acrylamide); Random copolymer; Flocculation; Temperature-responsive polymer; Solid–liquid separations; Consolidation; Sedimentation;
Interaction via in situ binding of CdS nanorods onto gelatin by Shihua Tang; Youqun Li (71-77).
Water-soluble CdSNRs were facilely synthesized in gelatin solution at pH 12.0. Negatively charged CdSNRs quenched the synchronous fluorescence of gelatin by forming a CdS/gelatin complex.Display Omitted► CdSNRs bond to amide and carboxylic groups of gelatin long chains through electrostatic interactions. ► The interaction of CdS with gelatin led to a more polar environment for tyrosine and tryptophan residues. ► The molecular structure of gelatin has been destroyed, and relevant physiological functions are lost or changed. ► The results provide useful information for exploring the mechanism of interaction between nanoparticle and fibrous protein.In situ interaction of CdS nanorods (CdSNRs) with gelatin was investigated at pH 12.0. UV–Visible, FT-IR, scanning electron microscopy, dynamic light scattering, synchronous fluorescence, and three-dimensional fluorescence spectroscopy methods were used. It was found that negatively charged CdSNRs quenched the synchronous fluorescence of gelatin by forming a CdS/gelatin complex. The synchronous fluorescence quenching data were analyzed according to Scatchard equation, and the binding constants and corresponding thermodynamic parameters ΔH, ΔG, and ΔS at three different temperatures were calculated. Small positive enthalpy (ΔH) and entropy (ΔS) values indicate that both electrostatic and hydrophobic forces played the major roles in the binding reaction of CdSNRs with gelatin. The effect of CdSNRs on the conformation of gelatin was also analyzed from both synchronous fluorescence and three-dimensional fluorescence spectra. The results provide useful information for exploring the chemical mechanism of interaction between nanomaterials and fibrous protein.
Keywords: Gelatin; CdS nanorod; Steady state fluorescence; Static quenching; Thermodynamic parameter;
Synthesis and characterization of novel thermo-responsive F68 block copolymers with cell-adhesive RGD peptide by Myoung-Hwa Cha; Jiyeon Choi; Bo Gyu Choi; Kwideok Park; Ik Hwan Kim; Byeongmoon Jeong; Dong Keun Han (78-85).
Thermoresponsive and injectable hydrogels consisting of F68, biodegradable oligomers, 4-META and RGD peptide were successfully synthesized. These modified F68 triblock copolymers consist of the PPO blocks core and the PEO blocks shell in aqueous solution. The alterations of hydrophobic interaction and chain mobility lead to the phase transition with increasing temperature.Display Omitted► Thermoresponsive and Injectable hydrogels consisting of F68, biodegradable oligomers, 4-META and RGD peptide were successfully synthesized. ► These modified F68 triblock copolymers consist of the PPO blocks core and the PEO blocks shell in aqueous solution. ► The alterations of hydrophobic interaction and chain mobility lead to the phase transition with increasing temperature. ► These hydrogel are anticipated to apply drug delivery and tissue engineering.Thermosensitive poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (PEO–PPO–PEO) triblock copolymer, Pluronic F68, containing a hydrophobic unit, oligo-(lactic acid)(oligo-LA) or oligo-caprolactone (oligo-CL), 2-META and RGD as side groups was successfully synthesized and characterized by 1H NMR, FTIR, and elemental analysis. Their aqueous solution displayed special gel–sol–gel phase transition behavior with increasing temperature from 10 to 70 °C, when the polymer concentration was above critical micelle concentration (CMC). The gel–sol phase diagram was investigated using tube inversion method, rheological measurement, and dynamic light scattering. Based on these results, the gelation properties of modified F68 were affected by several factors such as the composition of the substituents, chain length of oligo l-LA or oligo ε-CL, and the concentration of the polymer solutions. The unique phase transition behavior with temperature was observed by modified F68 triblock copolymer, composed of the PPO blocks core and the PEO blocks shell in aqueous solution. This phenomenon was elucidated using 1H NMR data; the alteration of hydrophobic interaction and chain mobility led to the formation of transparent gel, coexistence of gel–sol, and opaque gel. These hydrogels may be useful in drug delivery and tissue engineering.
Keywords: Thermosensitive hydrogel; Pluronic F68; Gel–sol transition; Biodegradable polymer; RGD peptide;
SBA-15 mesoporous silica coated with macrocyclic calixarene derivatives: Solid extraction phases for heavy transition metal ions by Bao-Lian Su; Xu-Chu Ma; Fen Xu; Li-Hua Chen; Zheng-Yi Fu; Nicolas Moniotte; Sami Ben Maamar; Roger Lamartine; Francis Vocanson (86-92).
Macrocyclic calixarene derivatives functionalized mesoporous SBA-15 showed high capacity for HTM ions extraction from aqueous solution and the present work can open a new exciting avenue for the preparation of new nanomaterials with integrated organic functional groups and advanced performances.Display Omitted► Macrocyclic calixarene derivatives functionalized mesoporous SBA-15. ► HTM ions extraction in aqueous solution. ► Environmental application.A layer of macrocyclic calixarene derivatives has been grafted on the internal surface of the mesochannels of the ordered mesoporous SBA-15 to develop highly efficient trap for heavy transition metal (HTM) ions. To ensure the successful anchoring of calixarene derivatives on the surface of SBA-15, two different types of calixarene derivatives, one with one trimethoxysilane functional group and another with two trimethoxysilane functional groups have been explored. XRD, N2 adsorption and TEM results provide strong evidence that the mesoporous structure of the supporting materials retain their long range ordering throughout the grafting process. Solid-state NMR, TG and FT-IR spectroscopy indicate that both types of calixarene derivatives can be well-anchored on the surface of the wall of SBA-15. Calixarene derivative with only one trimethoxysilane functional group showed high grafting efficiency compared to that with two trimethoxysilane functional groups due to the intramolecular and intermolecular polycondensation between two trimethoxysilane functional groups. The HTM ions extraction capacity in aqueous solution of macrocycle functionalized SBA-15 nanohybrides for a series of HTM ions has been studied. The obtained materials demonstrated very high HTM ions extraction capacity up to 96% for Pb2+ in aqueous solution.
Keywords: Mesoporous silica SBA-15; Surface functionalization; Calixarene derivatives; Solid extraction phase; Heavy transition metal ions;
Facile synthesis of 3D flowerlike CeO2 microspheres under mild condition with high catalytic performance for CO oxidation by Junfeng Li; Guanzhong Lu; Hongfeng Li; Yanqin Wang; Yun Guo; Yanglong Guo (93-99).
Three-dimensional hierarchical flowerlike CeO2 microspheres with high catalytic activity were successfully synthesized in very mild conditions, which were assembled by 1D nanowires formed by the aggregation of 0D nanoparticles.Display Omitted►Three-dimensional flowerlike CeO2 microspheres were firstly synthesized under very mild conditions (100 °C). ► An interesting mechanism for the formation of CeO2 microspheres was discussed. ► The synthesized CeO2 shows excellent catalytic performance for CO oxidation.Three-dimensional (3D) hierarchical flowerlike CeO2 microspheres with 5–8 μm diameter were hydrothermally synthesized by using multiple surfactants at very mild condition (100 °C) and characterized by XRD, low-temperature N2 adsorption, SEM, TEM, TG, FT-IR, and UV–vis spectroscopies. The results show that the flowerlike ceria prepared with the co-surfactant of sodium dodecyl sulfonic and PEG 600 possesses multilevel pore structure and low band gap energy. A possible formation mechanism of flowerlike ceria is that 3D flowerlike microspheres are assembled by 1D nanowires formed through an aggregation of 0D nanoparticles. Based on the unique structure and morphology, the prepared flowerlike CeO2 exhibits more amount of surface capping oxygen, higher concentrations of Ce3+ and O vacancy, and more (1 0 0) lattice planes, resulting in its higher catalytic activity for CO oxidation than general bulk ceria. Furthermore, photoluminescence property testing shows that flowerlike CeO2 exhibits the violet blue light emission with a blue shift, because of the quantum size effect, differing from general ceria.
Keywords: Flowerlike CeO2 microspheres; Facile synthesis; Mild condition; Co-surfactant technology; Catalytic CO oxidation;
Zeta potential of anoxygenic phototrophic bacteria and Ca adsorption at the cell surface: Possible implications for cell protection from CaCO3 precipitation in alkaline solutions by Irina A. Bundeleva; Liudmila S. Shirokova; Pascale Bénézeth; Oleg S. Pokrovsky; Elena I. Kompantseva; Stephanie Balor (100-109).
Electrophoretic mobility and Ca adsorption measurements demonstrate that anoxygenic phototrophic bacteria can metabolically control their surface potential to electrostatically attract the nutrients at alkaline pH, while rejecting/avoiding Ca ions to prevent CaCO3 precipitation in the vicinity of cell surface and thus, cell incrustation.Display Omitted► Anoxygenic phototrophic bacteria can metabolically control their surface potential. ► This regulation is necessary to electrostatically attract the nutrients at alkaline pH. ► It can be also related to rejecting Ca ions to prevent CaCO3 precipitation in the vicinity of cell surface.Electrophoretic mobility measurements and surface adsorption of Ca on living, inactivated, and heat-killed haloalkaliphilic Rhodovulum steppense, A-20s, and halophilic Rhodovulum sp., S-17-65 anoxygenic phototrophic bacteria (APB) cell surfaces were performed to determine the degree to which these bacteria metabolically control their surface potential equilibria. Zeta potential of both species was measured as a function of pH and ionic strength, calcium and bicarbonate concentrations. For both live APB in 0.1 M NaCl, the zeta potential is close to zero at pH from 2.5 to 3 and decreases to −30 to −40 mV at pH of 5–8. In alkaline solutions, there is an unusual increase of zeta potential with a maximum value of −10 to −20 mV at a pH of 9–10.5. This increase of zeta potential in alkaline solutions is reduced by the presence of NaHCO3 (up to 10 mM) and only slightly affected by the addition of equivalent amount of Ca. At the same time, for inactivated (exposure to NaN3, a metabolic inhibitor) and heat-killed bacteria cells, the zeta potential was found to be stable (−30 to −60 mV, depending upon the ionic strength) between pH 5 and 11 without any increase in alkaline solutions. Adsorption of Ca ions on A-20s cells surface was more significant than that on S-17-65 cells and started at more acidic pHs, consistent with zeta potential measurements in the presence of 0.001–0.01 mol/L CaCl2. Overall, these results indicate that APB can metabolically control their surface potential to electrostatically attract nutrients at alkaline pH, while rejecting/avoiding Ca ions to prevent CaCO3 precipitation in the vicinity of cell surface and thus, cell incrustation.
Keywords: Anoxygenic phototrophic bacteria; Rhodovulum sp.; Electrophoresis; Zeta potential; Calcium; Bicarbonate; Adsorption; Calcite;
The inhibition abilities of multifunctional polyelectrolytes for silica scale formation in cooling water systems: Role of the nonionic functional group by Ikuko Nishida; Yoshihiro Okaue; Takushi Yokoyama (110-116).
Relationship between experimental scale formation rate and calculated one which was obtained by correlation equation based on the interaction energies calculated by DFT.Display Omitted► The inhibition ability for silica scales was investigated based on the effect of aluminum. ► Polyelectrolytes with acrylic acid, sulfonic acid and nonionic monomers were examined. ► In order to clarify the quantitative factors affecting inhibition ability, regression analysis were applied. ► The effective inhibitors tend to disperse aluminum hydroxide and interact Si(OH)3O−.The abilities of multifunctional polyelectrolytes to enhance aluminum hydroxide dispersion and inhibit silica scale formation were examined in a pilot cooling water system. The following multifunctional polyelectrolytes were studied: a terpolymer of acrylic acid (AA), 2-acrylamide-2-methyl propane sulfonic acid (SA) and N-vinylpyrrolidone (NVP) (P(AA/SA/NVP)), acrylic acid homopolymer (P(AA)) and a copolymer of AA and SA (P(AA/SA)). The order of inhibition ability was P(AA/SA/NVP) > P(AA/SA) > P(AA), and was consistent with that of the dispersing ability for aluminum hydroxide. Other terpolymers incorporating different nonionic monomers were also examined and factors affecting their inhibition abilities were investigated, based on interaction energies calculated by density functional theory. Based on the correlation between scale inhibition abilities and interaction energies, we elucidated that the effective nonionic monomer of terpolymer for silica scale inhibition had low affinity for aluminum hydroxide and high affinity for H2O and Si(OH)3O−. The affinities of nonionic monomer for aluminum hydroxide and H2O suggested that there was proper conformation of polyelectrolyte adsorbed for effectively dispersing aluminum hydroxide. Also, high affinity of nonionic monomer for Si(OH)3O− suggested that interacting Si(OH)3O− is an important role of inhibition of silica scale formation.
Keywords: Silica scales; Aluminum hydroxide; Multifunctional polyelectrolyte; Cooling water systems;
Bridging flocculation of PEI-functionalized latex particles using nanocrystalline cellulose by Luca Manfredi; Reghan J. Hill; Theo G.M. van de Ven (117-123).
Nanocrystalline cellulose (NCC) can bridge polystyrene (PS) latex particles fuctionalized with polyethyleneimine (PEI). Upon addition of salt, the PEI–NCC bond is weakened, resulting in salt-induced stabilization.Display Omitted► Stable latex particles were produced grafted with linear polyethylene imine (PEI) chains and ethanolamine, which acts as a blocking agent. ► These particles can be flocculated by nanocrystalline cellulose (NCC). ► The aggregates can be broken up by adding salt, resulting in a restabilization of the suspension.Polystyrene microspheres were functionalized by covalent binding of 250 kDa linear PEI and ethanolamine, acting as a blocking agent, through bioconjugation with EDAC. The functionalized spheres were found to become less susceptible to salt-induced flocculation due to electrosteric stability, caused by the PEI chains at low NaCl concentrations, and at high salt concentration, by steric repulsion by the ethanolamine layer, which in combination with van der Waals attraction results in a shallow energy minimum and the formation of a few unstable aggregates. The latex aggregated in the presence of nanocrystalline cellulose (NCC) with varying efficiencies, depending on the ratio of NCC to latex particles in solution. Polyelectrolyte titration showed that each latex sphere contained about 15 grafted PEI chains. The fastest aggregation was detected when about half of these chains were covered by a single NCC particle.
Keywords: Flocculation; Nanocolloids; Bridging; Functionalized latex; Nanocrystalline cellulose; Blocking agent; Bioconjugation;
Analysis of HIV-1 fusion peptide inhibition by synthetic peptides from E1 protein of GB virus C by Maria Jesús Sánchez-Martín; Kalina Hristova; Montserrat Pujol; Maria J. Gómara; Isabel Haro; M. Asunción Alsina; M. Antònia Busquets (124-131).
Five peptides corresponding to the E1 protein of Hepatitis G virus have been selected as possible candidates for inhibiting the activity of the fusion peptide of HIV-1..Display Omitted► GBV-C related peptides as possible inhibitors of the HIV-1 FP insertion into bilayers. ► 5 out of 58 of the synthesized peptides are involved in the prevention of HIV-1 entry. ► The effect of HIV-1 FP on bilayers is illustrated by confocal microscopy. ► Spontaneous binding between E1 peptides and HIV-1 FP has been observed.The aim of this study was to identify proteins that could inhibit the activity of the peptide sequence representing the N-terminal of the surface protein gp41 of HIV, corresponding to the fusion peptide of the virus (HIV-1 FP). To do this we synthesized and studied 58 peptides corresponding to the envelope protein E1 of the hepatitis G virus (GBV-C).Five of the E1 synthetic peptides: NCCAPEDIGFCLEGGCLV (P7), APEDIGFCLEGGCLVALG (P8), FCLEGGCLVALGCTICTD (P10), QAGLAVRPGKSAAQLVGE (P18) and AQLVGELGSLYGPLSVSA (P22) were capable of inhibiting the leakage of vesicular contents caused by HIV-1 FP. A series of experiments were carried out to determine how these E1 peptides interact with HIV-1 FP. Our studies analyzed the interactions with and without the presence of lipid membranes. Isothermal titration calorimetry revealed that the binding of P7, P18 and P22 peptides to HIV-1 FP is strongly endothermic, and that binding is entropy-driven. Gibbs energy for the process indicates a spontaneous binding between E1 peptides and HIV-1 FP. Moreover, confocal microscopy of Giant Unilamellar Vesicles revealed that the disruption of the lipid bilayer by HIV-1 FP alone was inhibited by the presence of any of the five selected peptides.Our results highlight that these E1 synthetic peptides could be involved in preventing the entry of HIV-1 by binding to the HIV-1 FP. Therefore, the continued study into the interaction between GBV-C peptides and HIV-1 FP could lead to the development of new therapeutic agents for the treatment of AIDS.
Keywords: HIV-1 FP inhibition; Hepatitis G virus; Peptide synthesis; Bilayers as model membranes; Giant unilamellar vesicles; Confocal microscopy;
Surface modification of alumina nanofibres for the selective adsorption of alachlor and imazaquin herbicides by Blain Paul; Wayde N. Martens; Ray L. Frost (132-138).
Surface design of alumina nanofibres for the selective adsorption of pollutants.Display Omitted► This study focuses on the surface modification of γ-Al2O3 nanofibres by the grafting of two organosilane agents 3-chloropropyltriethoxysilane and octyl-triethoxysilane onto the surface. ► Those grafts can establish super hydrophobic sites along the surfaces which facilitate the selective removal of alachlor and imazaquin herbicides from water. ► The grafting process provides an efficient and extremely large uptake capacity occurred within the protruding adsorption sites.The effective removal of pollutants using a thermally and chemically stable substrate that has controllable absorption properties is a goal of water treatment. In this study, the surfaces of thin alumina (γ-Al2O3) nanofibres were modified by the grafting either of two organosilane agents, 3-chloro-propyl-triethoxysilane (CPTES) and octyl-triethoxysilane (OTES). These modified materials were then trialed as absorbents for the removal of two herbicides, alachlor and imazaquin from water. The formation of organic groups during the functionalisation process established super hydrophobic sites on the surfaces of the nanofibres. This super hydrophobic group is a kind of protruding adsorption site which facilitates the intimate contact with the pollutants. OTES grafted substrate were shown to be more selective for alachlor while imazaquin selectivity is shown by the CPTES grafted substrate. Kinetics studies revealed that imazaquin was rapidly adsorbed on CPTES-modified surfaces. However, the adsorption of alachlor by OTES grafted surface was achieved more slowly.
Keywords: Grafted alumina fibres; Adsorption; Water purification; Herbicides; TEM;
Self-assembly of short amyloidogenic peptides at the air–water interface by Nitin Chaudhary; Ramakrishnan Nagaraj (139-147).
Surface pressure modulates the self-assembled structures formed by short amyloidogenic peptides at air–water interface.Display Omitted► The amyloidogenic peptides Ac-DWSFYLLYYTEFT-am (Pβ2m) and Ac-VQIVYK-am (AcPHF6) are surface-active. ► Surface pressure and solvent used for deposition modulate their structures at air–water interface. ► Pβ2m forms fibrils at low surface pressures. At high surface pressures, fibrillar morphology is not discernible. ► AcPHF6 fibrils pack into sheet-like structures at high surface pressures. ► At low surface pressures, AcPHF6 structures show dependence on the solvent used for deposition.Short peptide stretches in amyloidogenic proteins can form amyloid fibrils in vitro and have served as good models for studying amyloid fibril formation. Recently, these amyloidogenic peptides have gained considerable attention, as non-amyloid ordered structures can be obtained from these peptides by carefully tuning the conditions of self-assembly, especially pH, temperature and presence of organic solvents. We have examined the effect of surface pressure on the self-assembled structures of two amyloidogenic peptides, Pβ2m (Ac-DWSFYLLYYTEFT-am) and AcPHF6 (Ac-VQIVYK-am) at the air–water interface when deposited from different solvents. Both the peptides are surface-active and form Thioflavin T (ThT) positive structures at the air–water interface. There is considerable hysteresis in the compression and expansion isotherms, suggesting the occurrence of structural rearrangements during compression. Preformed Pβ2m fibrillar structures at the air–water interface are disrupted as peptide is compressed to lower molecular areas but restored if the film is expanded, suggesting that the process is reversible. AcPHF6, on the other hand, shows largely sheet-like structures at lower molecular areas. The solvents used for dissolution of the peptides appear to influence the nature of the aggregates formed. Our results show that like hydrostatic pressure, surface pressure can also be utilized for modulating the self-assembly of the amyloidogenic and self-assembling peptides.
Keywords: Amyloidogenic peptides; Aromatic interactions; Surface activity; Fibrillar aggregation; Fluorescence microscopy; Compression isotherms;
Vesicle formation with amphiphilic chitosan derivatives and a conventional cationic surfactant in mixed systems by Yaxun Fan; Yan Liu; Juqun Xi; Rong Guo (148-153).
Vesicles are formed in the C n -OCMCS (n = 4, 6, 8)/CTAB mixed system.Display Omitted► Vesicles are formed in alkylated O-carboxymethylation chitosan (C n -OCMCS) and CTAB mixed systems. ► Increasing the hydrocarbon tail length of C n -OCMCS facilitates the formation of vesicles. ► Adding salt and increasing temperature can be used to control vesicle properties. ► Electrostatic and hydrophobic interaction and hydrogen bonding are all involved in vesicle formation.The self-assembly behavior of mixed systems consisting of amphiphilic chitosan derivatives C n -OCMCS (n = 4, 6, 8) and the conventional cationic surfactant cetyltrimethylammonium bromide (CTAB) is investigated. Transmission electron microscopy (TEM), dynamic light scattering (DLS), small-angle X-ray diffraction (XRD), UV–vis spectra, and zeta potential measurements have been utilized to characterize the microstructures of C n -OCMCS/CTAB mixtures in aqueous solutions. Spherical vesicles are formed spontaneously in the C n -OCMCS (n = 4, 6, 8)/CTAB mixed systems, and the increased hydrophobic chain length of C n -OCMCS enhances the ability to form vesicles. The addition of NaBr with higher concentrations to the vesicle system transforms vesicles into micelles, and an increase in temperature decreases the vesicle size. The results indicate that the main driving forces controlling vesicle formation may be attributed to the strong electrostatic interactions as well as the hydrophobic interactions, and also the hydrogen bonding between C n -OCMCS molecules.
Keywords: Amphiphilic chitosan derivatives; Self-assembly; Cationic surfactant; Vesicle;
NMR investigations of self-aggregation characteristics of SDS in a model assembled tri-block copolymer solution by B.V.N. Phani Kumar; S. Umayal Priyadharsini; G.K.S. Prameela; Asit Baran Mandal (154-162).
SDS self-aggregation characteristics in the absence and presence of the PEO–PPO–PEO tri-block copolymer [(EO)20–(PO)70–(EO)20], and also copolymer aggregation features in the presence of SDS, investigated using NMR diffusometry.Display Omitted► NMR diffusion study provides an opportunity to demonstrate polymer–surfactant interactions in distinct regimes of SDS. ► The obtained micelle pertinent parameters like cmc and hydrodynamic radius reveal the binding nature of polymer to SDS. ► The onset of secondary micelle concentration (C2) of SDS. ► The disintegration of polymer at higher SDS concentrations. ► The NMR results well corroborated by surface tension and conductivity data.The present work was undertaken with a view to understand the influence of a model non-ionic tri-block copolymer PEO–PPO–PEO (poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide)) with molecular weight 5800 i.e., P123 [(EO)20–(PO)70–(EO)20] on the self-aggregation characteristics of the anionic surfactant sodium dodecylsulfate (SDS) in aqueous solution (D2O) using NMR chemical shift, self-diffusion and nuclear spin-relaxation as suitable experimental probes. In addition, polymer diffusion has been monitored as a function of SDS concentration. The concentration-dependent chemical shift, diffusion data and relaxation data indicated the significant interaction of polymeric micelles with SDS monomers and micelles at lower and intermediate concentrations of SDS, whereas the weak interaction of the polymer with SDS micelles at higher concentrations of SDS. It has been observed that SDS starts aggregating on the polymer at a lower concentration i.e., critical aggregation concentration (cac = 1.94 mM) compared to polymer-free situation, and the onset of secondary micelle concentration (C 2 = 27.16 mM) points out the saturation of the 0.2 wt% polymer or free SDS monomers/micelles at higher concentrations of SDS. It has also been observed that the parameter cac is almost independent in the polymer concentrations of study. The TMS (tetramethylsilane) has been used as a solubilizate to measure the bound diffusion coefficient of SDS–polymer mixed system. The self-diffusion data were analyzed using two-site exchange model and the obtained information on aggregation dynamics was commensurate with that inferred from chemical shift and relaxation data. The information on slow motions of polymer–SDS system was also extracted using spin–spin and spin–lattice relaxation rate measurements. The relaxation data points out the disintegration of polymer network at higher concentrations of SDS. The present NMR investigations have been well corroborated by surface tension and conductivity measurements.
Keywords: NMR relaxation; Self-diffusion; Tri-block copolymer; SDS; PEO–PPO–PEO; Surface tension; Conductivity;
Biophysical investigation of the interfacial properties of cationic fluorocarbon/hydrocarbon hybrid surfactant: Mimicking the lung surfactant protein C by Nihal Aydogan; Burcin Uslu; Hacer Tanaci (163-174).
The novel cationic surfactant that bears a fluorocarbon chain forms a partially mixed monolayer with lipids at the air-water interface. That monolayer displays some of the behavior of lung surfactant, specifically the ones attributed to the presence of Lung Surfactant Protein C (SP-C). Presence of small amount of that cationic molecule at the interface increases the surface fluidity of the monolayer and affects the cyclic compression/expansion behavior of the interface as SP-C.Display Omitted► A new lipid molecule was designed to mimic the selected properties of the lung surfactant. ► The molecule bears a cationic head group and a fluorocarbon chain in its structure. ► It interacts with lipids to adjust the interfacial fluidity, elasticity and the hysteresis. ► Mimicing the lung surfactant behaviour associated with specific lung surfactant protein C is achieved.The interfacial behavior of the newly designed Fluorocarbon Hydrocarbon Cationic Lipid (FHCL or CH3(CH2)17N+(C2H5)2(CH2)3(CF2)7CF3I−) and its mixtures with a phospholipid (DPPC, Dipalmitoylphosphatidylcholine) at different mole fractions were investigated. This new molecule was synthesized to mimic the selected properties of lung surfactant, which is a natural lipid–protein mixture which is known to play important roles in the process of respiration, by considering the structure/function relation of lung surfactant protein (SP-C). Each segment in the molecular structure was selected to affect the molecular level interaction at the interface whereas the keeping the overall structure as simple as possible. The surface pressure area isotherms obtained for the mixtures of DPPC/FHCL indicated that there was repulsive interaction between DPPC and FHCL molecules. Due to the molecular level interaction, specifically at mole fraction 0.3, the isotherm obtained from that mixture resembled the isotherm obtained from the DPPC monolayer in the presence of SP-C. High elasticity of the interface was one of the important parameters for the respiration process, therefore, shear and dilatational elasticities of two-component systems were determined and they were found to be similar to the case where SP-C protein is present. Fluorescence microscopy images were taken in order to investigate the monolayer in details. The FHCL was able to fluidize the DPPC monolayer even at high surface pressures effectively. In addition, the cyclic compression–expansion isotherms were obtained to understand the spreading and re-spreading ability of the pure FHCL and the mixed DPPC/FHCL monolayers. At a specific mole fraction, X FHCL = 0.3, the mixture exhibited good hysteresis in area, compressibility, recruitment index and re-spreading ability at the interface. All these results point out that FHCL can fulfill the selected features of the lung surfactant that are attributed to the presence of SP-C protein when mixed with DPPC, even if the molecular structure of the FHCL is quite simple.
Keywords: Fluorinated surfactants; Langmuir monolayer; Lung surfactant; SP-C; Hysteresis; Elasticity;
Studies on the mixed micelles of alkyltrimethylammonium bromides and butanediyl-1,4-bis(alkyldimethylammonium bromide) dimeric surfactants in the presence and absence of ethylene glycol at different temperatures by P. Ajmal Koya; Kabir-ud-Din (175-181).
Variation of X 1 Ideal , X 1 Rub , X 1 Rod of C m TAB + m–4–m, 2Br− (m = 14 and 16) against C m TAB mole fractions in EG-W (30:70 v/v) mixed solvent media, T = 298.15 K.Display Omitted► Mixed micellization of dimeric surfactants in mixed solvent media is reported. ► Mixtures show significant deviation from ideal behavior. ► Micellar mole fractions of monomeric components > ideal mole fractions. ► Type of interaction depends on the bulk mole fractions of the components.Mixed micellization of two cationic dimeric surfactants butanediyl-1,4-bis(alkyldimethylammonium bromide) [ C m H 2 m + 1 N + ( CH 3 ) 2 – ( CH 2 ) 4 – N + ( CH 3 ) 2 C m H 2 m + 1 , 2 Br - ] with their monomeric counterparts alkyltrimethylammonium bromides [ C m H 2 m + 1 N + ( CH 3 ) 3 Br - ](m = 14 and 16) has been studied at different temperatures (298.15–323.15 K) in presence and absence of ethylene glycol (EG) using conductivity data. Steady state fluorescence quenching (SSFQ) measurements were performed to estimate the average aggregation number (Nagg ) of the mixed micelles at 298.15 K. The ideal cmc values, experimental and ideal micellar compositions, interaction parameters, activity coefficients of the components, etc. have been evaluated by considering theoretical models of Clint, Rubingh and Rodenas. The analysis reveals that the fraction of the monomeric surfactant in the mixed micelles is higher than the expected ideal micellar mole fraction, and in most of the cases mixed micelles of the studied components become more ideal in the presence of EG.
Keywords: Mixed micelles; Critical micelle concentration; Average aggregation number; Interaction parameter; Ethylene glycol–water mixed solvent medium;
Effects of nonionic micelles on the rate of alkaline hydrolysis of N-(2′-methoxyphenyl)phthalimide (1): Kinetic and rheometric evidence for a transition from spherical to rodlike micelles under the typical reaction conditions by Yoke-Leng Sim; Nor Saadah M. Yusof; Azhar Ariffin; M. Niyaz Khan (182-188).
Kinetic studies and rheological measurements showed the transition from spherical to rodlike micelles occurs at ∼50 mM C16E20, ∼1.4 mM C12E23 and ∼3.0 mM C18E20.Display Omitted► Evidence is presented for failure of the pseudophase micellar model for kinetic data analysis of micellar-mediated reaction(s). ► Rheometric data indicate a transition from spherical to rodlike micelles at a certain value of Rt (= [nonionic surf]/[NaOH]). ► The kinetic data fail to obey pseudophase micellar model at R ⩾ Rt . ► Rheometric and kinetic data show the micellar structural transition at R ⩾ Rt .Pseudo-first-order rate constants (kobs ) for alkaline hydrolysis of N-(2′-methoxyphenyl)phthalimide (1) decrease nonlinearly with increasing total concentration of nonionic surfactant C m E n (i.e. [C m E n ] T where m and n represent the respective number of methyl/methylene units in the tail and polyoxyethylene units in the headgroup of a surfactant molecule and m/n = 16/20, 12/23 and 18/20) at constant 2% v/v CH3CN and 1.0 mM NaOH. The kobs vs. [C m E n ] T data follow the pseudophase micellar (PM) model at ⩽50 mM C16E20, ⩽1.4 mM C12E23 and ⩽2.0 mM C18E20 where rate of hydrolysis of 1 in micellar pseudophase could not be detected. The values of kobs fail to follow the PM model at > ∼50 mM C16E20, > ∼1.4 mM C12E23 and > ∼2.0 mM C18E20 which has been attributed to a micellar structural transition from spherical to rodlike which in turn increases C m E n micellar binding constant (KS ) of 1 with increasing values of [C m E n ] T . Rheological measurements show the presence of spherical micelles at ⩽50 mM C16E20, ⩽1.4 mM C12E23 and ⩽3.0 mM C18E20. The presence of rodlike micelles is evident from rheological measurements at > ∼50 mM C16E20, > ∼1.4 mM C12E23 and > ∼3.0 mM C18E20.
Keywords: N-(2′-Methoxyphenyl)phthalimide; Nonionic surfactant; Pseudophase micellar model; Spherical micelles; Rodlike micelles;
Magnetically separable polyoxometalate catalyst for the oxidation of dibenzothiophene with H2O2 by Zhenxin Zhang; Fengwei Zhang; Qianqian Zhu; Wei Zhao; Baochun Ma; Yong Ding (189-194).
H3PW12O40 supported on surface-modified Fe3O4 magnetite nanoparticles was prepared using an easy synthetic route and successfully applied for the oxidation of dibenzothiophene.Display Omitted► Two H3PW12O40–functionalized Fe3O4 magnetic nanoparticles of Fe3O4–PEI–PW12O40 and Fe3O4–SiO2–NH2–PW12O40 were synthesized. ► Selectivity oxidation of dibenzothiophene to dibenzothiophene sulphone and dibenzothiophene sulfoxide was studied. ► The catalyst could be easily separated from the reaction system by adding a magnet and reused for several times.Two types of polyoxometalate-functionalized magnetic nanoparticles catalysts consisting of H3PW12O40 supported on surface-modified Fe3O4 magnetite nanoparticles were prepared using an easy synthetic route and successfully applied for the oxidation of dibenzothiophene. The magnetic catalysts showed a catalytic performance in the oxidation of dibenzothiophene in acetonitrile with hydrogen peroxide, and high conversions were obtained. The catalysts could be easily separated from the reaction solution by applying an external magnetic field and recycled several times.
Keywords: Superparamagnetic nanoparticles; Magnetic properties; Polyoxometalate; Oxidation; Catalyst recycling;
Zeta potential of particle bilayers on mica: A streaming potential study by Maria Zaucha; Zbigniew Adamczyk; Jakub Barbasz (195-203).
Controlled formation of particle bilayers.Display Omitted► Formation of a particle bilayer can be studied using the streaming potential method. ► The zeta potential of bilayers approach 0.71 of the bulk value of particles forming the external layer. ► Experimental data can be used for interpretation of polyelectrolyte films in LbL processes. ► Our results can be used as reference systems for interpretation of the antigen/antibody interactions.The streaming potential of mica covered by bilayers of latex particles was measured using the parallel-plate channel cell. The size of the first latex (A500) bearing amidine charged groups was 503 nm and the second latex (L800) bearing sulfonate groups was 810 nm (at pH 5.5 and an ionic strength of 10−2 M). The A500 latex exhibited an isoelectric point at pH 10.5, whereas the L800 latex was strongly negative at all pH. Mica sheets were precovered first by the A500 latex particles under diffusion transport conditions. The coverage of this supporting layer was regulated between 0.02 and 0.5 by changing the bulk concentration of latex and the deposition time. Then, the second layer of the L800 latex of regulated coverage up to 0.55 was deposited under the diffusion transport. The coverage of particles and their distributions in both layers were determined by a direct enumeration of particles by optical microscopy under wet conditions and by AFM. It was shown that the structure of the L800 particle layers and the maximum coverage were in accordance with theoretical simulations performed according to the random sequential adsorption (RSA) model. After forming bilayers of desired composition and structure, streaming potential measurements were carried out. The influence of the mica substrate, the supporting layer coverage, and its zeta potential on the apparent zeta potential of bilayers was systematically studied. It was established that for a bilayer coverage exceeding 0.20, the net zeta potential became independent of the substrate and the supporting layer zeta potentials. Then, the asymptotic values of the zeta potential of the bilayer approach 1 / 2 = 0.71 of the bulk zeta potential of the particles forming the external (second) layer. This behavior was interpreted theoretically in terms of the electrokinetic model derived previously for monolayers. It was also concluded that results obtained in this work can be exploited for interpretation of polyelectrolyte film formation in the layer by layer (LbL) processes and protein adsorption pertinent to the antigen/antibody interactions.
Keywords: Bilayers of latex particles; Deposition of particles on mica; Latex particles on mica; Mica covered by particles; Streaming potential of particle covered surfaces; Zeta potential of particles on mica; Zeta potential of particle-covered surfaces;
Specific vapor sorption properties of phosphorus-containing dendrimers by Alexander V. Gerasimov; Marat A. Ziganshin; Alexander E. Vandyukov; Valeri I. Kovalenko; Valery V. Gorbatchuk; Anne-Marie Caminade; Jean-Pierre Majoral (204-210).
Independent sorption of guest vapors in phosphorus dendrimer gives a specific size exclusion effect and does not exclude guest exchange..Display Omitted► Phosphorus dendrimers have different selectivity for different homological series of guests. ► The absence of plasticization of phosphorus dendrimer with good guest was observed. ► The guest exchange helps to overcome guest-binding irreversibility by phosphorus dendrimer.Specific combination of guest sorption properties was observed for phosphorus-containing dendrimers, which distinguish them from ordinary polymers and clathrate-forming hosts. The sorption capacity for 30 volatile guests, binding reversibility, guest desorption kinetics and guest exchange, glass transition behavior and ability to be plasticized with guest were studied for phosphorus dendrimers of different generations (G 1–G 4 and G 9) using quartz crystal microbalance sensor, FTIR microspectroscopy, atomic force microscopy, simultaneous thermogravimetry and differential scanning calorimetry combined with mass-spectrometry of evolved vapors. The dendrimers were found to have a different selectivity for different homological series of guests, high glass transition points without plasticization with guest even at high temperatures and saturation levels, moderate guest-binding irreversibility and ability both for effective guest exchange and independent guest sorption. These properties constitute an advantage of the studied dendrimers as receptor materials in various applications.
Keywords: Dendrimers; Vapor sorption; Guest exchange; QCM sensor; Thermogravimetry; Differential scanning calorimetry; FTIR microspectroscopy;
Simulating the changes in carbon structure during the burn-off process by Sylwester Furmaniak; Artur P. Terzyk; Piotr A. Gauden; Nigel A. Marks; Rebecca C. Powles; Piotr Kowalczyk (211-219).
Selected structures of studied “soft” carbons.Display Omitted► Virtual activation of ‘soft’ carbon leads to similar changes in porosity to experimental. ► The relationship between the location of a maximum on the APD curve and the pore diameter is general. ► The application of popular methods of porosity characterisation can lead to wrong conclusions.Using a simple energetic criterion, we modelled the process of activation of ‘soft’ activated carbons. Eighteen carbon samples, differing in degree of graphitisation, and obtained using Molecular Dynamics annealing of an amorphous carbon precursor were studied. For all samples, the geometric pore size distribution was calculated using the method proposed by Bhattacharya and Gubbins. Adsorption isotherms for Ar at 87 K were simulated and analysed using different approaches widely applied in adsorption science (αs , DA, APD, ND, BET). It is shown that our approach leads to similar changes in microporosity (with the rise in carbon burn-off) to those observed in real experiments. Moreover, the conclusions about the reality of popular methods of carbon porosity characterisation are given.
Keywords: Activated carbon; Adsorption activation; Porosity; Molecular simulations; Porosity; VPC;
Acid natural clinoptilolite: Structural properties against adsorption/separation of n-paraffins by Aramis Rivera; Tania Farías; Louis Charles de Ménorval; Giselle Autié-Castro; Hernany Yee-Madeira; José Luis Contreras; Miguel Autié-Pérez (220-226).
The adsorption and separation of n-paraffins on a modified natural clinoptilolite were studied by inverse gas chromatography at infinite dilution.Display Omitted► Use of an acid natural clinoptilolite in the adsorption and separation of n-paraffins mixtures. ► Structural characterization of the zeolitic materials. ► Employment of the inverse gas chromatography at infinite dilution (IGCID) for the adsorption and separation studies.The employment of an acid natural clinoptilolite (AZH-1) in the adsorption and separation of n-paraffins has been evaluated. Natural clinoptilolite, NZ, was the raw material used to prepare the sodium-exchanged clinoptilolite (AZ) starting from which the AZH-1 sample was obtained by acid treatment. The structural stability of the samples after the applied treatments was demonstrated. The nitrogen adsorption experiments indicated that the acid sample has a homogeneous porous distribution and a considerable increase in the micropore volume with respect to NZ and AZ. The employment of the inverse gas chromatography at infinite dilution (IGCID) allowed studying the adsorption and separation of n-paraffin mixtures on AZH-1. It was also confirmed that the diffusion on AZH-1 took place in an unblocked structure through the A channel of ten members with minimal interactions. The IGCID results demonstrated the capacities of the acid Cuban natural zeolite in the adsorption and separation of n-paraffin mixtures.
Keywords: Acid treatment; Natural clinoptilolite; Adsorption; Separation; n-Paraffins;
Removal of diphenhydramine from water by swelling clay minerals by Zhaohui Li; Po-Hsiang Chang; Wei-Teh Jiang; Jiin-Shuh Jean; Hanlie Hong; Libing Liao (227-232).
Possible interlayer conformations of adsorbed DPH on MMT.Display Omitted► Montmorillonite is a good adsorbent for diphenhydramine (DPH) in aqueous solution. ► Cation exchange is the dominant mechanism for DPH adsorption. ► At high adsorption DPH intercalated into the interlayer of montmorillonite. ► Adsorption of DPH resulted in interlayer dehydration of montmorillonite.Frequent detection of pharmaceuticals in surface water and wastewater attracted renewed attention on studying interactions between pharmaceuticals and sludge or biosolids generated from wastewater treatment. Less attention was focused on studying interactions between pharmaceuticals and clay minerals, important soil and sediment components. This research targeted on investigating interactions between diphenhydramine (DPH), an important antihistamine drug, and a montmorillonite, a swelling clay, in aqueous solution. Stoichiometric desorption of exchangeable cations accompanying DPH adsorption confirmed that cation exchange was the most important mechanism of DPH uptake by the swelling clay. When the solution pH was below the pK a of DPH, its adsorption on the swelling clay was less affected by pH. Increasing solution pH above the pK a value resulted in a decrease in DPH adsorption by the clay. An increase in d 001 spacing at a high DPH loading level suggested interlayer adsorption, thus, intercalation of DPH. The results from this study showed that swelling clays are a good environmental sink for weak acidic drugs like DPH. In addition, the large cation exchange capacity and surface area make the clay a good candidate to remove cationic pharmaceuticals from the effluent of wastewater treatment facilities.
Keywords: Adsorption; Cation exchange; Dehydration; Diphenhydramine; Intercalation; Montmorillonite;
Effect of surface acidity and basicity of aluminas on asphaltene adsorption and oxidation by Nashaat N. Nassar; Azfar Hassan; Pedro Pereira-Almao (233-238).
Percentage conversion ratio curves of asphaltene oxidation in the presence and absence of different aluminas.Display Omitted► Alumina particles with varying surface acidity could be used for enhanced asphaltene adsorption and/or oxidation. ► Acidic alumina has high adsorption capacity for asphaltenes. ► Basic alumina has significant catalytic effect toward oxidation of asphaltenes. ► A correlation appears to exist between the adsorption affinity and the catalytic activity of aluminas, the higher the affinity for asphaltene adsorption.This study investigates the effect of surface acidity and basicity of aluminas on asphaltene adsorption followed by air oxidation. Equilibrium batch adsorption experiments were conducted at 25 °C with solutions of asphaltenes in toluene at concentrations ranging from 100 to 3000 g/L using three conventional alumina adsorbents with different surface acidity. Data were found to better fit to the Freundlich isotherm model showing a multilayer adsorption. Results showed that asphaltene adsorption is strongly affected by the surface acidity, and the adsorption capacities of asphaltenes onto the three aluminas followed the order acidic > basic and neutral. Asphaltenes adsorbed over aluminas were subjected to oxidation in air up to 600 °C in a thermogravimetric analyzer to study the catalytic effect of aluminas with different surface acidity. A correlation was found between Freundlich affinity constant (1/n) and the catalytic activity. Basic alumina that has the lowest 1/n value, depicting strongest interactions, has the highest catalytic activity, followed by neutral and acidic aluminas, respectively.
Keywords: Asphaltenes; Oxidation; Adsorption; Activation energy; Alumina;
Theory of membrane capacitive deionization including the effect of the electrode pore space by P.M. Biesheuvel; R. Zhao; S. Porada; A. van der Wal (239-248).
A theoretical model is presented for capacitive water desalination describing ion adsorption in electrostatic double layers in porous electrodes and salt storage in electrode macropores.Display Omitted► Membrane capacitive deionization is a novel electrokinetic water desalination technology using millifluidic flow-cells. ► Improved dynamic transport theory is presented to describe salt removal and storage in porous carbon electrodes. ► Detailed comparison is made between experimental data and theoretical model predictions.Membrane capacitive deionization (MCDI) is a technology for water desalination based on applying an electrical field between two oppositely placed porous electrodes. Ions are removed from the water flowing through a channel in between the electrodes and are stored inside the electrodes. Ion-exchange membranes are placed in front of the electrodes allowing for counterion transfer from the channel into the electrode, while retaining the coions inside the electrode structure. We set up an extended theory for MCDI which includes in the description for the porous electrodes not only the electrostatic double layers (EDLs) formed inside the porous (carbon) particles, but also incorporates the role of the transport pathways in the electrode, i.e., the interparticle pore space. Because in MCDI the coions are inhibited from leaving the electrode region, the interparticle porosity becomes available as a reservoir to store salt, thereby increasing the total salt storage capacity of the porous electrode. A second advantage of MCDI is that during ion desorption (ion release) the voltage can be reversed. In that case the interparticle porosity can be depleted of counterions, thereby increasing the salt uptake capacity and rate in the next cycle. In this work, we compare both experimentally and theoretically adsorption/desorption cycles of MCDI for desorption at zero voltage as well as for reversed voltage, and compare with results for CDI. To describe the EDL-structure a novel modified Donnan model is proposed valid for small pores relative to the Debye length.
Keywords: Porous carbon electrodes; Electrokinetics; Water desalination; Capacitive deionization; Ion-exchange membranes; Modified Donnan model; Electrostatic double layer models; Nernst–Planck equation;
Self-assembly of C60, SWNTs and few-layer graphene and their binary composites at the organic–aqueous interface by Piyush Chaturbedy; H.S.S. Ramakrishna Matte; Rakesh Voggu; A. Govindaraj; C.N.R. Rao (249-255).
Self-assembly of C60, single-walled carbon nanotubes, few-layer graphene and composites of these nanocarbons have been studied at toluene-water interface. The morphologies and charge-transfer interactions in the films are investigated.Display Omitted► Self-assembly of nanocarbons at the organic–aqueous interface. ► Concentration and time dependent morphological studies of the films formed at the interface. ► Charge-transfer interaction in the composites formed by two nanocarbons.Self-assembly of C60, single-walled carbon nanotubes (SWNTs) and few-layer graphene at the toluene-water interface has been investigated, starting with different concentrations of the nanocarbons in the organic phase and carrying out the assembly to different extents. Morphologies and structures of the films formed at the interface have been investigated by electron microscopy and other techniques. In the case of C60, the films exhibit hcp and fcc structures depending on the starting concentration in the organic phase, the films being single crystalline under certain conditions. Self-assembly of the composites formed by pairs of nanocarbons (C60–SWNT, C60–few-layer graphene and SWNT–few-layer graphene) at the interface has been studied by electron microscopy. Raman spectroscopy and electronic absorption spectroscopy of the films formed at the interface have revealed the occurrence of charge-transfer interaction between SWNTs and C60 as well as between few-layer graphene and C60.
Keywords: Fullerenes; SWNTs; Few-layer graphene; Self-assembly; Liquid–liquid interface; Charge-transfer;
Size-distribution of droplets in emulsions by statistical mechanics calculation by Koichi Aoki (256-261).
Which distribution is more stable?Display Omitted► This is a revisit of theoretical estimation of size-distributions of emulsions by statistical mechanics. ► The size distribution in equilibrium was localized both to the smallest and the largest droplets. ► The largest ones have a main contribution in the volume fraction. ► They are formed kinetically by competition of diffusion with gravitational convection. ► The concept is useful for emulsion polymerization, size-control of dispersed nanoparticles and ion transfer at oil|water interfaces.This report is concerned with theoretical demonstration of the spontaneous emulsification which has been observed in a soft contact of nitrobenzene with water without surfactant [K. Aoki, M. Li, J. Chen, T. Nishiumi, Electrochem. Commun. 11 (2009) 239]. The demonstration is based on the model of spherical oil droplets with any size in equilibrium. The droplets are composed of the smallest droplets, the total number of which is given. An assembly of small droplets has larger surface energy than that of large ones because the surface energy is proportional to the surface area. The former has larger configurational entropy than the latter because the number of small droplets is bigger than that of the large ones. Since the free energy is determined by the competition between the surface energy and the entropy, it is not clear which assembly has lower free energy. This question was solved numerically here by statistical mechanics calculation of the size distributions, which contained only a parameter of the surface energy. The results of the computation at small number of droplets were used for deriving approximate equations for extremely large number of droplets. The size distribution was localized both to the smallest and the largest droplets. The diameter of the largest droplet was estimated from the dynamics in which coalescence by diffusion of droplets is disturbed by gravitational convection. The size then predicted was of the order of micrometer, being close to experimental values.
Keywords: Emulsions; Droplets formed by surface energy; Statistical mechanics; Distribution of particle size; Phase separation;
Streaming current and wall dissolution over 48 h in silica nanochannels by Mathias Bækbo Andersen; Henrik Bruus; Jaydeep P. Bardhan; Sumita Pennathur (262-271).
By: (a) self-consistent coupling of wall and electrolyte bulk; (b) accounting for pressure-driven flow and 2D geometry; (c) measuring streaming currents over 48 h; we (d) estimate silica dissolution rates.Display Omitted► Fabrication and modeling of bare and cyanosilane-coated fused silica nanochannels. ► 2D modeling coupling chemical equilibrium theory for surface and bulk. ► Continuous measurements of streaming currents in silica nanochannels over 48 h. ► Developed method for determination of dissolution rates of silica under confinement.We present theoretical and experimental studies of the streaming current induced by a pressure-driven flow in long, straight, electrolyte-filled nanochannels. The theoretical work builds on our recent one-dimensional model of electro-osmotic and capillary flow, which self-consistently treats both the ion concentration profiles, via the nonlinear Poisson–Boltzmann equation, and the chemical reactions in the bulk electrolyte and at the solid–liquid interface. We extend this model to two dimensions and validate it against experimental data for electro-osmosis and pressure-driven flows, using eight 1-μm-wide nanochannels of heights varying from 40 nm to 2000 nm. We furthermore vary the electrolyte composition using KCl and borate salts, and the wall coating using 3-cyanopropyldimethylchlorosilane. We find good agreement between prediction and experiment using literature values for all parameters of the model, i.e., chemical reaction constants and Stern-layer capacitances. Finally, by combining model predictions with measurements over 48 h of the streaming currents, we develop a method to estimate the dissolution rate of the silica walls, typically around 0.01 mg/m2/h, equal to 45 pm/h or 40 nm/yr, under controlled experimental conditions.
Keywords: Nanofluidics; Silica dissolution; Gouy–Chapman–Stern model; Streaming current; Cyanosilane surface coating;
Design and fabrication of a superhydrophobic glass surface with micro-network of nanopillars by Joonsik Park; Hyuneui Lim; Wandoo Kim; Jong Soo Ko (272-279).
A transparent superhydrophobic glass surface with a micro-network of nanopillars was developed via colloidal lithography and the mechanical robustness of nanopillars on surface was confirmed through a finger rubbing test.Display Omitted► Transparent superhydrophobic glass surface with a micro-network of nanopillars.Nanopillars are fabricated via colloidal lithography and plasma etching. ► Mechanical robustness of network of nanopillars is confirmed through a finger rubbing test. ► Size-dependent contact angle equation is proposed at high contact angle (>135°) and Bond number ≪ 1. ► Furmidge’s sliding angle equation is modified just considering static contact angle.The wetting property of a superhydrophobic glass surface with a micro-network of nanopillars fabricated from colloidal lithography and plasma etching is investigated in this paper. The micro-network distribution of nanospheres can be modulated by diluting the nanosphere concentration and controlling the spin rate. The micro-network of nanospheres spun on the glass surface serves as a mask for nanopillars during the plasma etching process. After the fabrication, the nano-structured surface is treated with fluoroalkylsilane self-assembled monolayers to obtain superhydrophobicity. Among several spin rates, the minimum colloidal network area density from a 100 nm polystyrene nanosphere solution diluted to 0.026% was found at a spin rate of 4000 rpm. The sample with the lowest network area density shows a good quality of superhydrophobicity, having the highest water contact angle and the lowest sliding angle among samples with other network area densities. In particular, samples with a micro-network of pillars also showed mechanical robustness against finger rubbing. To assess the superhydrophobic behavior in-depth, a size-dependent contact angle equation is proposed for use with a high contact angle (>135°) and with a Bo (Bond number) ≪ 1. Furmidge’s sliding angle equation is also modified; it is derived considering a static contact angle to simplify the prediction of the sliding angle. The contact and sliding angle measurements from samples with a micro-network of nanopillars show good agreement with the proposed equations.
Keywords: Superhydrophobic glass; Micro-network of nanopillars; Mechanical robustness; Size-dependent contact angle; Sliding angle;
Liquid phase formation of alkyl- and perfluoro-phosphonic acid derived monolayers on magnesium alloy AZ31 and their chemical properties by Takahiro Ishizaki; Katsuya Teshima; Yoshitake Masuda; Michiru Sakamoto (280-288).
This study demonstrates preparation and estimation of chemical properties of phosphonic acid derived self-assembled monolayer prepared on magnesium alloy by liquid phase.Display Omitted► Phosphonic acid derived self-assembled monolayers (SAMs) were formed on magnesium alloy by liquid phase method. ► Chemical bonding states between the SAMs and magnesium alloy were investigated using X-ray photoelectron spectroscopy. ► Chemical stability and corrosion resistance of the SAMs on magnesium alloy increased with an increase in the alkyl chain length.Alkyl- and perfluoro-phosphonic acid derived SAMs were successfully formed on Mg alloy by liquid phase method for the first time. The chemical and anticorrosive properties of the prepared SAMs on magnesium alloys were characterized using contact angle measurements, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and electrochemical measurements. Water contact angle measurements revealed that the maximum advancing/receding water contact angles of n-octyl (OP: CH3(CH2)7PO(OH)2), n-dodecyl (DP: CH3(CH2)11PO(OH)2), n-octadecyl (ODP: CH3(CH2)17PO(OH)2) phosphonic acid, and 2-(perfluorohexyl)ethyl (PFEP: CF3(CF2)5CH2CH2PO(OH)2) phosphonic acid were 105.1/64.7°, 108.3/69.6°, 111.9/75.2°, and 115.2/67.4° respectively. In the case of alkylphosphonic acid SAMs (OP, DP, and ODP), the advancing and receding water contact angles increased with an increase in the preparation time. The angle-resolved XPS (AR-XPS) data revealed that the film thicknesses of the OP, DP, ODP, PFEP on Mg alloy were estimated to be 0.8, 1.2, 1.7, and 1.1 nm, respectively. The XPS O 1s data support that the phosphonic acid derived SAM is covalently bound to the oxide or hydroxide surface of the Mg alloy in a monodenate or bidenate manner. Chemical stability of the alkyl- and perfluoro-phosphonic acid modified Mg alloy surfaces was investigated using aqueous solutions at pH = 4.0, 7.0, and 10.0. The contact angles of OP, DP, and PFEP modified Mg surface decreased rapidly within the first 5 min after immersion in all the aqueous solutions and were less than 20°. On the other hand, the contact angles of the ODP modified Mg alloy after immersion in aqueous solutions at pH 4, 7 and 10 for 5 min were 45.1°, 89.3,° and 85.5°, respectively. The ODP modified Mg alloy had highest chemical stability in four types of the phosphonic acid derived SAMs used in this study, indicating that the molecular density of ODP on Mg alloy would be higher than those of OP, DP, PFEP on Mg alloy. The corrosion resistance of ODP modified Mg alloy was investigated by potentiodynamic polarization curve measurements. The ODP modified Mg alloy exhibits protective properties in a solution containing Cl− ions compared to unmodified Mg alloy.
Keywords: Self-assembled monolayer; Mg alloy; Wetting property; Corrosion resistance;
Morphology and interphase formation in epoxy/PMMA/glass fiber composites: Effect of the molecular weight of the PMMA by D. Olmos; K. Bagdi; J. Mózcó; B. Pukánszky; J. González-Benito (289-299).
SEM micrographs (8000×) from the freeze fractured surfaces of the different ternary systems (glass fiber reinforced epoxy/PMMA) showing the different interfacial morphology in the close vicinity of the fiber: (a) EP(PMMA-34)-GF; (b) EP(PMMA-65)-GF; (c) EP(PMMA-76)-GF and (d) EP(PMMA-360)-GF.Display Omitted► Interphases of epoxy–PMMA (5 wt.%) modified polymer reinforced with GF were studied. ► Four PMMA (M w = 34,000, 65,000, 76,000 and 360,000 g/mol) were chosen for this work. ► In the presence of GF, a new phase with more restricted mobility appears. ► The amount of this phase increases as molecular weight of PMMA does.In this work ternary composites based on an epoxy thermoset modified with a thermoplastic polymer and reinforced with glass fibers were prepared. The aim of this study is to analyze the influence of the molecular weight of the thermoplastic polymer on the final morphologies. To obtain tailor made interphases four poly(methylmethacrylate), PMMA, which differ in their molecular weight (34,000, 65,000, 76,000 and 360,000 g/mol) were chosen to modify the epoxy resin. The amount of PMMA in the composites was fixed to 5 wt.%. Neat polymer matrices (epoxy-PMMA without fibers) were also prepared for comparison. To study all systems dynamic mechanical analysis (DMA), atomic force microscopy (AFM) and scanning electron microscopy (SEM) were used. Although all the systems showed the typical phase separation in the epoxy/PMMA blend, DMA experiments revealed a new phase with more restricted mobility when the glass fibers are present. The amount of this phase increases as molecular weight of PMMA does. The morphologies as well as the fracture surface in the immediate surroundings of the fibers were found to be different from those observed further away from the surface of the fiber, suggesting therefore that, in this case, different fracture mechanism operates. These observations allow us to conclude that an interphase with specific properties is formed. This interphase is based on a polymer or a polymer blend (epoxy-PMMA) enriched in the component with lower mobility.
Keywords: Glass fiber; Modified epoxy; Thermoplastic; Interfacial morphology;
Fabrication of superhydrophobic polymer films with hierarchical silver microbowl array structures by Miaojun Xu; Nan Lu; Dianpeng Qi; Hongbo Xu; Yandong Wang; Shoulei Shi; Lifeng Chi (300-304).
Superhydrophobic films with hierarchical silver bowl array structures were prepared by thermally evaporating silver on monolayer templates of self-assembled PS spheres.Display Omitted► The present fabrication method for flexible superhydrophobic films allows for a large area fabrication. ► The prepared superhydrophobic films show excellent stability after bending strongly the surfaces. ► The synthesized films exhibit uniform wettability over the whole surface. ► The superhydrophobic films could find applications as self-cleaning curved surfaces.Flexible superhydrophobic polyvinyl alcohol (PVA) films with silver bowl-like array structure are fabricated based on the thermal evaporation with sphere monolayer as templates and the modification of 1H, 1H, 2H, 2H-perfluorodecanethiol on silver surface. The silver microbowl arrays were composed of silver nanoparticles with an average diameter size of ca. 10 nm. The polymer films exhibit excellent stability and remarkable superhydrophobicity with a high water contact angle (CA) of about 163° and a low sliding angle (SA) of less than 3°.
Keywords: Silver microbowl array; Hierarchical structure; Flexible superhydrophobic film; Silver nanoparticles; Template; Stability;
Nanostructured Ag surface fabricated by femtosecond laser for surface-enhanced Raman scattering by Han-Wei Chang; Yu-Chen Tsai; Chung-Wei Cheng; Cen-Ying Lin; Yen-Wen Lin; Tzong-Ming Wu (305-308).
The SERS intensity of R6G in aqueous solution at the prepared nanostructured Ag surface is 15 times greater than that of an untreated Ag substrate.Display Omitted► Femtosecond laser is effective for the preparation of SERS-active substrate. ► Nanostructured Ag surface exhibits higher SERS intensity. ► This work is potential for determination of low concentration molecules.Femtosecond laser was employed to fabricate nanostructured Ag surface for surface-enhanced Raman scattering (SERS) application. The prepared nanostructured Ag surface was characterized by field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The FESEM images demonstrate the formation of nanostructure-covered femtosecond laser-induced periodic surface structure, also termed as ripples, on the Ag surface. The AFM images indicate that the surface roughness of the produced nanostructured Ag substrate is larger than the untreated Ag substrate. The XRD and XPS of the nanostructured Ag surface fabricated by femtosecond laser show a face centered cubic phase of metallic Ag and no impurities of Ag oxide species. The application of the produced nanostructured Ag surface in SERS was investigated by using rhodamine 6G (R6G) as a reference chemical. The SERS intensity of R6G in aqueous solution at the prepared nanostructured Ag surface is 15 times greater than that of an untreated Ag substrate. The Raman intensities vary linearly with the concentrations of R6G in the range of 10−8–10−4 M. The present methodology demonstrates that the nanostructured Ag surface fabricated by femtosecond laser is potential for qualification and quantification of low concentration molecules.
Keywords: SERS; R6G; Ag nanostructure; Femtosecond laser;
Synthesis of palladium colloids within polydimethylsiloxane and their use as catalysts for hydrogenation by Dean J. Campbell; Josiah D. Miller; Brad J. Andersh (309-312).
Unreacted silanes within cured polydimethylsiloxane (PDMS) reduce tetrachloropalladate(II) ions, generating PDMS-encapsulated palladium colloids, which catalyze successive hydrogenation reactions without loss of activity.Display Omitted► Reduction of tetrachloropalladate(II) by cured PDMS yields encapsulated colloids. ► Pd/PDMS vessels are effective hydrogenation catalysts. ► No loss of catalytic activity was observed after ten hydrogenation reactions. ► Pd/PDMS vessels can be stored for at least 6 months without loss of activity. ► PDMS encapsulation reduces the pyrophoric behavior of hydrogen-exposed Pd.The presence of unreacted silanes within cured polydimethylsiloxane (PDMS) leads to the reduction of tetrachloropalladate(II) ions, generating encapsulated palladium colloids. The resulting colloids had varied morphology and were typically less than 80 nm in size. The Pd/PDMS vessels, which contained 0.10 ± 0.01% Pd, were effective catalysts for the hydrogenation of carbon–carbon multiple bonds for at least ten successive runs with no loss of catalytic activity, and the catalyst does not exhibit the same pyrophoric behavior as Pd on carbon after use in hydrogenation reactions. In addition, storage of previously used Pd/PDMS vessels for 6 months in air did not affect the catalytic activity, and the overall morphology of the catalysts after use was the same as those that have not been involved in catalytic reactions.
Keywords: Palladium; Colloid/nanoparticle; Polydimethylsiloxane/PDMS/silicone; Catalysis; Hydrogenation;
Semi-empirical description of the constant β in the equation of state for interfacial tension by Peter J. Skrdla (313-316).
A relationship is derived for β showing its possible dependence on the surface area, heat capacity and thermal expansion coefficient of the three phases in equilibrium (at constant temperature and pressure).Display Omitted► A physicochemically relevant description of the constant, β, in the Equation of State (EOS) for interfacial tension is presented. ► The semi-empirical Eq. is based on EOS assumptions and fundamental concepts from Classical Nucleation theory (CNT). ► The derivation proceeds from Eq. and Eq. , to provide more detail on β. ► Both Eq. and Eq. are validated using data from the literature.A semi-empirical expression for the constant, β, in the Equation of State (EOS) for interfacial tension is proposed that exhibits a dependence on the surface area, heat capacity and thermal expansion coefficient of each of the materials involved in the three phase equilibrium (at constant temperature and pressure). The “wetting function”, which yields values between zero and unity as the contact angle, θ, varies from 0° to 180°, is also employed in the description of β. Empirical data is used to support that equation as well as the initially proposed relationship leading to its derivation that is based entirely on Classical Nucleation theory (CNT) outcomes and a “difference of the squares” correction term for the liquid–vapor and solid–vapor interfacial tensions.
Keywords: Equation of State (EOS); Interfacial tension; Contact angle; Correction factor;
General equation describing wetting of rough surfaces by Edward Bormashenko (317-319).
cos θ ∗ = r Φ S cos θ + Φ S - 1 - Γ γ ξ + 1 a The general equation describing wetting of rough surfaces considering the line tension induced effects is derived. The equation comprises the Cassie, Wenzel and Wong–Ho equations as particular cases.Display Omitted► General equation describing wetting of rough surfaces is derived. ► The problem of wetting is discussed in the framework of the variational approach. ► Transversality conditions are exploited for deriving the equation. ► The equation considers the effects related to the line tension. ► The equation comprises as particular cases the Cassie, Wenzel and Wong–Ho equation.The problem of wetting is discussed in the framework of the variational approach. Derivation of the general equation describing the wetting of rough chemically homogenous surfaces is presented. The equation considers effects related to the line tension at the perimeter of the drop and at the details of the relief. The equation comprises as particular cases the Cassie and Wenzel equations and the equation proposed recently by Wong and Ho.
Keywords: Wetting; Rough surfaces; Cassie wetting; Wenzel wetting; Line tension; Variational approach; Transversality conditions;
Fabrication of split-ring resonators by tilted nanoimprint lithography by Liguo Gao; Li Lin; Juanyuan Hao; Weifeng Wang; Renping Ma; Hongbo Xu; Jingsheng Yu; Nan Lu; Wenchong Wang; Lifeng Chi (320-323).
It is an efficient technique for fabricating large area periodic metallic split-ring arrays by using tilted nanoimprint lithography. The molds can be used multiple times without a loss of fidelity.Display Omitted► In this study, an efficient fabrication technique for large area Negative-index materials has been demonstrated. ► Periodic metallic split-ring arrays are fabricated based on the combination of tilted nanoimprint lithography and nanotransfer imprinting. ► The feature size of the split-rings can be adjusted to 240 nm by scaling down the nanopillars of original imprinting mold. ► This approach provides an alternative method for the large-area fabrication of SRRs.An efficient fabrication technique for large area periodic metallic split-ring arrays has been demonstrated by the combination of tilted nanoimprint lithography and nanotransfer imprinting. The feature size of the split-rings can be adjusted by varying the key geometry parameters of the original imprinting mold. Due to the flexible nature of PDMS molds, these arrays can be patterned on curved surfaces. The molds for nanoimprint lithography and nanotransfer imprinting can be used multiple times without a loss of fidelity.
Keywords: Negative-index material; Split-ring resonator; Tilted nanoimprint lithography; Nanotransfer printing; Reactive ion etching;