Journal of Colloid And Interface Science (v.350, #1)

Cover 1 (OFC).

On the applicability of the Brinkman equation in soft surface electrokinetics by Stanislav S. Dukhin; Ralf Zimmermann; Jérôme F.L. Duval; Carsten Werner (1-4).
The applicability of the Brinkman equation within the field of soft surface electrokinetics is discussed.The Stokes equation is commonly used within the field of electrokinetics of hard impermeable surfaces while the Brinkman equation is adopted for tackling hydrodynamics in the framework of soft (permeable) surface electrokinetics (SSE). The latter was initially proposed for modeling the hydrodynamics in so-called hybrid systems that consist of a porous medium and an adjacent fluid phase basically because the conventional Darcy law or Debye and Bueche model initially proposed for that purpose failed to provide the required velocity and shear stress-continuity conditions at the porous media–fluid interface. However, even though the physical background of the Brinkman equation and its boundary conditions have been discussed when applied to the hydrodynamics of hybrid systems, controversy still remains with respect to their applicability in the field of SSE. Indeed, recent experiments pointed out better agreement between shear flow into a regular array of rods oriented across the flow and the solution of the Brinkman equation for hybrid systems providing a stress-jump boundary condition is taken into account (M.F. Tachie et al., J. Fluid. Mech. 493 (2003) 319). As there is identity in the Brinkman model for hybrid systems and for SSE, the question arises whether the above discontinuity of viscous stress must be incorporated or not into SSE modeling. Recent determination of hydrodynamic penetration length λ o - 1 of swollen and collapsed thermo-responsive films (J.F.L. Duval, R. Zimmermann, A.L. Cordeiro, N. Rein, C. Werner, Langmuir 25 (2009) 10691) suggests that there is no need for a cardinal revision of the Brinkman model, although further experimental investigations are required to support such a conclusion. With regard to these experiments, almost complete agreement between independent determination of λ o - 1 by swelling experiments and its derivation according to Brinkman model was obtained.
Keywords: Brinkman equation; Soft surface electrokinetics; Hydrodynamic penetration length; Shear flow penetration; Non-Darcy flow;

Fabrication, spectroscopy, and dynamics of highly luminescent core–shell InP@ZnSe quantum dots by Mee Rahn Kim; Jae Hun Chung; Mihee Lee; Seonghoon Lee; Du-Jeon Jang (5-9).
Highly luminescent core–shell InP@ZnSe quantum dots have been prepared via hot injection synthesis, and their photoluminescence spectroscopy and dynamics have been investigated using static and time-resolved spectroscopy.Display Omitted► Highly luminescent core-shell InP@ZnSe quantum dots have been prepared via hot injection synthesis. ► The roles of the surface passivation of QDs on photoluminescence have been probed by time-resolved spectroscopy. ► The photoluminescence of InP@ZnSe QDs is stronger by 6.8 times than that of InP QDs.InP quantum dots of 3 nm in diameter have been prepared using a dehalosilylation reaction and passivated with ZnSe to enhance photoluminescence by 6.8 times. Core–shell InP@ZnSe quantum dots dispersed in n-hexane have then been investigated using time-resolved spectroscopy to understand their photoluminescence dynamics. The observed decay times of 0.1, 7, and 1100 ns have been attributed to the relaxation times of electrons in the conduction band, trap sites, and surface states. The surface-state luminescence of core–shell InP@ZnSe quantum dots having the maximum at 760 nm has been distinguished spectrally and dynamically from their band-edge emission having the maximum at 620 nm or from their trap-site emission having the maximum at 660 nm.
Keywords: Lifetime; Nanoparticle; Photoluminescence; Semiconductor; Trap emission;

Cholesterol induced CTAB micelle-to-vesicle phase transitions by Mary Cano-Sarabia; Angelina Angelova; Nora Ventosa; Sylviane Lesieur; Jaume Veciana (10-15).
■■■Vesicles prepared by self-assembly of a hydrated mixture of a cationic surfactant (cetyltrimethylammonium bromide) and a lipid (cholesterol) are studied as potential nanocarriers for the delivery of active ingredients. The understanding of the mechanism of the micelle-to-vesicle transition involved in the vesicle formation appears to be crucial regarding the stability of the vesicles as nanovectors. Here, UV–Vis spectroscopy is used to monitor the phase transition from micelles to vesicles promoted by the progressive addition of cholesterol to CTAB micellar solutions. The employed solvatochromic indicator, pinacyanol chloride (PIN), is a cyanine dye that is highly sensitive to the polarity of the medium. The self-assembly between the CTAB and the cholesterol molecules is investigated by means of turbidity (optical density) measurements as well.
Keywords: Cationic vesicle; Critical micellar concentration; Self-assembly; Phase transition mechanism; Cetyltrimethylammonium bromide; Cholesterol;

The chemical and morphological properties of CoNi alloy nanoparticles, formed by co-evaporation onto freshly cleaved highly oriented pyrolytic graphite (HOPG) surfaces, have been studied by ToF-SIMS, XPS, SEM and AFM.Display Omitted► CoNi alloy nanoparticles are formed by co-evaporation onto HOPG surfaces. ► Even under UHV, the NPs react with residual gases to form surface contaminants. ► The Co component of the alloy is the more reactive. ► Alloying increases the reactivity of Ni.CoNi alloy nanoparticles, formed by co-evaporation onto freshly cleaved highly oriented pyrolytic graphite (HOPG) surfaces, have been studied using time-of-flight secondary ion mass spectrometry (ToF-SIMS), X-ray photoelectron spectroscopy (XPS), and scanning electron (SEM) and atomic force (AFM) microscopies. ToF-SIMS detected Co x Ni y fragments, indicating alloy formation. Even under ultra-high vacuum, the nanoparticles reacted with residual C- and O-containing gases to form surface contaminants (carbides, oxides, etc.) as revealed by both XPS and ToF-SIMS. On prolonged exposure to air, both the zerovalent metal and carbide peaks of each component decreased with time, as each metal reacted with atmospheric oxygen; as with the pure metals, the Co component of the alloy was the more reactive.
Keywords: CoNi co-deposition; Metal–metal interaction; Metal nanoparticle alloy formation; XPS;

Dual responsive copolymer micelles for drug controlled release by Liangrong Yang; Chen Guo; Lianwei Jia; Xiangfeng Liang; Chunzhao Liu; Huizhou Liu (22-29).
The CSO-g-Pluronic copolymer micelles synthesized via a facile Dess–Martin activation method represents an attractive temperature and pH responsive volume transition property.pH- and temperature-responsive polymeric drug carriers based on Chitosan oligosaccharide (CSO)-g-Pluronic copolymers were successfully synthesized for Doxorubicin (DOX) controlled release. The critical aggregation concentration of CSO-g-Pluronic is 0.035 mg/mL at 25 °C. The CSO-g-Pluronic and DOX-loaded CSO-g-Pluronic micelles have an average hydrodynamic diameter of 23.3 nm and 43.6 nm respectively at 30 °C and pH 7.0 with narrow size distribution. The temperature or pH responsive behavior of the micelles was characterized by dynamic light scattering, fluorescence spectroscopy, and zeta Potential Analysis. The temperature-dependent micellar transformation was induced by dehydration of Pluronic segments at higher temperature. The pH responsive volume increase was traced to the electrostatic repulsion between CSO segments from protonation of amino groups under acidic conditions. Consequently, the DOX release time was prolonged by CSO-g-Pluronic micelles at body temperature of 37 °C, and the DOX release was accelerated at mild acidic conditions (i.e. the pH environment around tumor tissues). The temperature- and pH-responsive properties of CSO-g-Pluronic copolymer have provided promising potentials for biomedical and biotechnological applications.
Keywords: Temperature responsive; pH responsive; Polymeric micelles; Drug controlled release;

Shape-controlled synthesis of F-substituted hydroxyapatite microcrystals in the presence of Na2EDTA and citric acid by Deli Jiang; Di Li; Jimin Xie; Jianjun Zhu; Min Chen; Xiaomeng Lü; Shengchun Dang (30-38).
High-quality F-substituted hydroxyapatite solid and hollow microcrystals with various novel shapes were fabricated via a facile hydrothermal method based on the use of Na2EDTA, citric acid, and doping ions (F) itself.Display Omitted► A combination of Na2EDTA and citric acid (CA) yields a series of high-quality FHAp microcrystals with tunable shapes. ► The double-chelating-agent system enables an investigation of the effect of individual calcium chelating agents on the growth of FHAp microcrystals. ► The double-chelating-agent system is capable of making FHAp hollow microcrystals with tunable shapes. ► F ions were found to play multiple roles in shaping FHAp microcrystals.We present a facile strategy for the shape-controlled synthesis of F-substituted hydroxyapatite (FHAp) microcrystals based upon using a combination of Na2EDTA and citric acid (CA). Novel, well-defined FHAp microcrystals of various shapes, such as hexagonal disks with predominant (0 0 0 1) faces, hexagonal shuttles, hexagonal prisms, icosahedrons, and hexagonal microrods with tunable aspect ratios, were fabricated. In particular, FHAp hollow microcrystals with tunable shapes were fabricated directly without using any additional template. The central features of our approach are the use of both Na2EDTA and CA as two distinct chelating reagents and the use of substitution ions (F) itself as a growth inhibitor for the FHAp crystals. F ions were found to play a critical role in the formation of hexagonally shaped FHAp microcrystals, and in the one-pot formation of hollow microcrystals, which relies on the addition order of F ions in the synthesis.
Keywords: Hydroxyapatite; F-substituted; Microcrystal; Shape-controlled synthesis; Chelating agent; Hollow;

Synthesis and characterization of porous shell-like nano hydroxyapatite using Cetrimide as template by P. Michael S.L. Shanthi; R.V. Mangalaraja; A.P. Uthirakumar; S. Velmathi; T. Balasubramanian; M. Ashok (39-43).
We report the successful preparation of shell-like nano HAp spheres with fine morphology and uniform size around 200 nm with porosity using the surfactant Cetrimide at CMC.Macromolecules of various surfactants and polymers are being used to prepare nano hydroxyapatites (HAp) of varied morphology. Here we report the successful preparation of shell-like nano HAp spheres with fine morphology, uniform size around 200 nm, and stoichiometry ratio 1.7 with 56% nano- (<5 nm) and 44% mesoporosity using the surfactant tetradecyltrimethylammonium bromide (Cetrimide), which was not reported earlier. The critical micelle concentration (CMC) of Cetrimide was calculated as 3.88 mM at room temperature, and based on that, the other parameters of the experiment were determined. The experiment was conducted at ambient temperature and normal pressure without any temperature control, which was considered a crucial parameter in the earlier works. Thus, this method is suitable to bulk production of HAp. All the inspections confirm the successful preparation of shell-like nano HAp spheres that are suitable for biomedical applications.
Keywords: Hydroxyapatite; Cationic surfactant; Cetrimide; Critical micelle concentration; Porous;

Synthesis and grafting of folate–PEG–PAMAM conjugates onto quantum dots for selective targeting of folate-receptor-positive tumor cells by Yili Zhao; Sen Liu; Yapeng Li; Wei Jiang; Yulei Chang; Si Pan; Xuexun Fang; Y. Andrew Wang; Jingyuan Wang (44-50).
Specific binding of the FPP-coated QDs to the surface of HeLa cells by membrane expression of FA-receptors in tumor cells.We report the design and synthesis of folate–poly(ethylene glycol)–polyamidoamine (FPP)-functionalized CdSe/ZnS quantum dots (QDs), in which the QD plays a key role in imaging, whereas the folate–poly(ethylene glycol) (PEG) conjugates of the polyamidoamine (PAMAM) dendrimer serve as a system targeted to folate receptors in tumor cells. Dendrimer ligands such as folate–PEG grafted PAMAM of generation 3.5 are found to encapsulate and solubilize luminescent QDs through direct ligand-exchange reactions. Because of membrane expression of FA receptors in tumor cells, this class of ligand-exchanged QDs is able to target tumor cells. We have evaluated FPP-coated QDs and QDs without folate in HeLa cells and shown that cellular uptake of FPP-coated QDs is more significant than that non folate QDs in vivo imaging experiment. In particular, QDs coated with FPP are initially bound to tumor cell surfaces, followed by slow endosomal escape and release into the tumor cells. These insights are important for the design and development of nanoparticle agents for optical detection of tumor cells and bio-imaging.
Keywords: Quantum dots; PEG; Target; Tumor cells; Bio-imaging;

Study of ferrofluids in confined geometry by Sangeeta Rawat; Dietmar Fink; Amita Chandra (51-57).
Passage of swift heavy ions (350 MeV, Au26+ ions) through dielectric layer (SiO2) on a Si substrate results in track formation in the dielectric layer. Etching of these tracks followed by filling by a suitable material (ferrofluids in the present case) results in modified electrical behaviour of the system. The IV behaviour in the presence/absence of external magnetic field of such a system is given in this paper.The passage of swift heavy ions through dielectric layers (SiO2 or SiON) on silicon, creates ion tracks in them. After the etching and filling of these ion tracks with a suitable material, a novel electronic structure acronymed TEMPOS – ‘Tunable Electronic Materials with Pores in Oxide on Silicon’ has been realized. Several electronic devices, both, active and passive, have been fabricated and systematically studied in the last few years. Sensors have also been successfully made and characterized using the TEMPOS structure as it offers a high surface to volume ratio resulting in fast response time and high sensitivity of the sensor. In continuation with these studies, in the present paper, ferrofluids have been inserted in the ion tracks to study their behaviour in confined geometry and for subsequently obtaining magnetic sensors. A comparative study has been done between the aqueous and non-aqueous ferrofluids. Insertion of the ferrofluids in the ion tracks exhibits a change in the IV behaviour in the presence of a magnetic field which can be exploited for obtaining the above said sensor.
Keywords: Swift heavy ions; Etched ion tracks; TEMPOS structure; Ferrofluid; Magnetic sensor;

Preparation of metal@silica core–shell particle films by interfacial self-assembly by Tao Liu; Dongsheng Li; Yu Zou; Deren Yang; Hailong Li; Yimin Wu; Minhua Jiang (58-62).
Oil–water interfacial self-assembly was used to prepare a series of films consisting of closely packed metal@silica particles.Display Omitted► Oil-water interfacial self-assembly is used to prepare metal@silica films. ► Extinction properties of metal@silica films depend on the metal core particles. ► Silica layers control the coupling between neighboring metal core particles. ► Metal@silica particle films display high SERS effect.A universal self-assembly method is used to prepare a series of large-area silica-coated metal particle (metal@silica) films at the hexane/water interface. The decrease of hexane/water interfacial energy after the particle adsorption leads to the formation of films. Since external silica shells eliminate the coupling between neighboring metal core particles, the extinction peaks of closely packed metal@silica particle films are as narrow as those of monodispersed metal particles. In the detection of Raman scattering signals of R6G dyes by shell-isolated nanoparticle-enhanced Raman spectroscopy, the use of metal@silica particle films resulted in an average enhancement by a factor of 105.
Keywords: Nanoparticle; Self-assembly; Optical property; Surface plasmon; Surface-enhanced Raman scattering;

PEO-b-PMAA gives PMAA-core micelles when the PMAA block is made insoluble by the addition of Ca2+ and forms PEO-core micelles when the cloud point of PEO is lowered to room temperature by the addition of PO 4 3 - .Display Omitted► Addition of Ca2+ to the aqueous solution of PEO-b-PMAA forms PMAA-core micelles. ► Addition of EDTA to the PMAA-core micelles leads to the formation of unimer. ► Addition of PO4 3− to the unimer solution gives micelles with PEO-core. ► Removal of PO4 3− by dialysis leads back to the formation of unimer.Two distinct types of micelle structures have been successfully obtained from poly(ethylene oxide-b-methacrylic acid) (PEO-b-PMAA) in aqueous solutions: one with a PEO-core surrounded by a PMAA corona and the other with a PMAA-core surrounded by a PEO-corona. The PEO-core micelles were obtained by decreasing the cloud point of the PEO to room temperature by adding phosphate ions PO 4 3 - , and the PMAA-core micelles were obtained by reducing the solubility of the PMAA block by adding calcium ions (Ca2+). The reversibility between the PMAA-core and PEO-core micelles was also confirmed; (1) the transformation from the PMAA-core to PEO-core micelles was achieved by solubilizing the PMAA block by removing Ca2+ with ethylenediaminetetraacetic acid followed by the addition of PO 4 3 - , and (2) the reverse transformation was carried out by removing PO 4 3 - by dialysis followed by the addition of Ca2+. The two types of micelles were characterized using various techniques such as turbidimetry, dynamic light scattering, scanning electron microscopy and electrophoretic light scattering.
Keywords: Schizophrenic; Micelles; Cloud point; Polyethylene oxide; Polymethacrylic acid; Phosphate ions;

Various reactants had different adsorption features due to their combinations with the SiO2 surface. More reactants distributed in the adsorption layer, smaller particles would form homogeneously on the SiO2 surface.Four reaction systems were employed to investigate the distribution of different reactants and its effects on the formation of particles by adsorption phase synthesis. Reactants such as Zn2+, Cu2+ and NaOH had different adsorption features on SiO2 due to their various combinations with the SiO2 surface. When the reactants were enriched on the silica surface, particles with size of several nanometers could be producted homogeneously on the SiO2 surface. In the preparation experiments of water concentration dependence and temperature dependence, the increasing concentration of adsorbed reactant was in favor of the formation of smaller particles although there was interference from other factors, such as thickness of the adsorption layer and the reaction kinetics.
Keywords: Adsorption layer; Nanoparticles; Nanoreactor; Reactant distribution;

Rhodamine B-anchored silica nanoparticles display white-light photoluminescence and are appliable to prepare photoluminescent PMMA films and nanofibers.This work reports white-light photoluminescent (PL) silica nanoparticles and their applications of preparation of PL polymer films and nanofibers. Rhodamine B (RhB) physically adsorbs or chemically bonds to silica nanoparticle (SNP) surfaces, resulting in PL SNPs. The RhB-modified SNPs exhibit white-light PL emissions under an excitation at 365 nm, which is different from the inherent yellow light emission of RhB. The SNPs with physically-adsorbed RhB show stimuli-responsive properties. In solutions, the RhB molecules which physically adsorb to SNPs release from SNPs, consequently turning the PL emission from white-light to yellow. On the other hand, the SNPs having covalently-bonded-RhB molecules are effective additives for preparation of white-light PL polymer composites. Both PL poly(methylmethacrylate) (PMMA) films (from casting process) and nanofibers (from electrospinning process) showing white-light PL emission have been prepared.
Keywords: White-light photoluminescence; Silica nanoparticles; Rhodamine B;

Rapid synthesis of a versatile organic/inorganic hybrid material based on pyrogenic silica by M. Becuwe; F. Cazier; P. Woisel; D. Landy; F. Delattre (83-89).
Versatile derivative of pyrogenic silica are synthesized by ultrasonic irradiation in a very short time and with high loading of organic fragments. The emergence of a mesoporosity is observed.Display Omitted► Amorphous fumed silica is functionalized by chlorobenzylated group. ► Chlorobenzylated silica is obtained by non-conventional methods. ► The ultrasonic procedure is the most convenient method. ► The chlorobenzylated silica is mesoporous.An efficient approach has been developed to synthesize a new versatile organo-silica material by non-conventional method (microwave irradiation and ultrasonic vibration) from amorphous pyrogenic silica and has been compared with thermic procedure. The samples were fully characterized by FTIR, solid-state 29Si and 13C CP/MAS NMR, thermogravimetric analysis (TGA), elemental analysis, scanning electron microscopy (SEM) and by N2-sorption isotherms measurements. The functionalization of silicon dioxide by 4-(chloromethylphenyl) trichlorosilane has been easily achieved by ultrasound irradiation in a very short time with high loading of organic fragments. Significant different sizes of pores were observed according to conventional or non-conventional synthesis procedure. In addition, new structural properties have been created with the emergence of a mesoporosity.
Keywords: Synthesis; Silicon dioxide; Ultrasound; Microwave; Versatile material;

Synthesis of magnetic and fluorescent multifunctional hollow silica nanocomposites for live cell imaging by Lei Sun; Yang Zang; Mingda Sun; Hengguo Wang; Xuanjing Zhu; Shufei Xu; Qingbiao Yang; Yaoxian Li; Yaming Shan (90-98).
Folate-conjugated magnetic and luminescent hollow silica nanocomposites are prepared for live cells fluorescence imaging.Display Omitted► Multifunctional hollow silica spheres in mixed water–ethanol solvents were synthesized. ► Multifunctional hydrophobic nanoscaled particulates were assembled in a single entity. ► Folate-conjugated magnetic and luminescent hollow silica spheres were used for cell imaging.In this paper, we report a synthesis of multifunctional core/shell silica nanocomposites in mixed water–ethanol solvents at room temperature. Water-soluble CTAB-stabilized nanoparticles (Fe3O4 and quantum dots) are used as templates and tetraethoxysilane (TEOS) is used as a precursor to fabricate multifunctional hollow silica nanocomposites. Owing to the high abundance of folate receptors in many cancer cells, folic acid is used as the targeting ligand. By coupling with folic acids, the multifunctional silica nanocomposites conjugates are successfully used for tumor cell imaging. In vitro cellular uptakes of such SiO2 nanocomposites are investigated with fluorescence microscope, which demonstrate much higher internalization of the folate-decorated SiO2 nanocomposites by Hela cancer cells which are of over-expression of folate receptors than the cellular uptake by NIH 3T3 fibroblast cells which are of low expression of folate receptors. Magnetic manipulation, fluorescence imaging, hollow structure, and cell targeting are simultaneously possible using a multifunctional silica nanocomposite. Our results demonstrate a robust hydrophobic nanoparticles-based approach for preparing multifunctional and biocompatible hollow silica composites, which could be also suitable for silica coating of other kinds of nanoparticles.
Keywords: Multifunctional; Magnetism; Fluorescence; Hollow nanostructures; Silica; Imaging;

Pyrene-probe fluorescence shows that only PE10500 with relatively balanced hydrophilic/phobic structure undergoes self-association in nonpolar solvents which is the basis for high efficiency of polypropylene surface modification by entrapment.Display Omitted► Homopolymers have low efficiency for entrapment into polypropylene surface ► Amphiphilic (macro) molecules with balanced structure are most efficient modifiers ► Diffusion of small amphiphilic molecule dominates entrapment behavior ► Balanced structure of amphiphilic polymer promotes reverse micellization and increases entrapment efficiencyEntrapment of a variety of ethyleneoxide-containing substances from nonpolar solutions into polypropylene (PP) microfiltration membrane surface for hydrophilic modification was studied. The results from gravimetric weight gain, surface characterization by contact angle measurements and ATR-IR spectroscopy, water flux measurements and protein adsorption revealed that poly(ethylene glycol)s (PEGs) were ineffective, while many nonionic amphiphilic substances, especially some tri-block copolymers of poly(ethyleneoxide) (PEO) and poly(propylene oxide) (PPO) were very effective for PP surface modification. The relationship between modifier structure and architecture and entrapment behavior was investigated by studying the micellization of the amphiphilic modifiers in nonpolar solutions via pyrene-probe fluorescence and 1H NMR spectroscopy. We observed that the balanced structure of nonionic tri-block (macro)molecules tended to promote the formation of reverse micelles. For the most efficient polymeric modifiers, the lowest reverse critical micelle concentration (RCMC) had been observed. We conclude that a block copolymer structure and architecture promoting the self-association in the nonpolar solvent is the basis for a high modification efficiency, and that reverse micelles are involved in the entrapment modification performed at concentrations above RCMC. A different mechanism has been deduced for amphiphilic modifiers with low molar mass. This work provides more comprehensive insights in surface entrapment as a easy to perform physical surface modification method for polymeric materials.
Keywords: Entrapment; PP microfiltration membrane; Nonionic amphiphilic (macro)molecules; Nonpolar; Reverse micelle;

Self-assembled monolayers of silver nanoparticles firmly grafted on glass surfaces: Low Ag+ release for an efficient antibacterial activity by Piersandro Pallavicini; Angelo Taglietti; Giacomo Dacarro; Yuri Antonio Diaz-Fernandez; Matteo Galli; Pietro Grisoli; Maddalena Patrini; Giorgio Santucci De Magistris; Robertino Zanoni (110-116).
A stable monolayer of silver nanoparticles is easily obtained on glass surfaces, capable of local antibacterial effect due to partial Ag → Ag+ oxidation with no NP release.A two-step, easy synthetic strategy in solution has been optimized to prepare authentic monolayers of silver nanoparticles (NP) on MPTS-modified glass surfaces, that were investigated by AFM imaging and by quantitative silver determination techniques. NP in the monolayers remain firmly grafted (i.e. not released) when the surfaces are exposed to air, water or in the physiological conditions mimicked by phosphate saline buffer, as UV–Vis spectroscopy and AFM studies demonstrate. About 15% silver release as Ag+ ions has been found after 15 days when the surfaces are exposed to water. The released silver cations are responsible of an efficient local microbicidal activity against Escherichia coli and Staphylococcus aureus bacterial strains.
Keywords: Antibacterial surface; Silver nanoparticles; Self-assembled monolayer;

Multifunctional pluronic/poly(ethylenimine) nanoparticles for anticancer drug by Na Li; Xingguo Yang; Guangxi Zhai; Lingbing Li (117-125).
The nanoparticles consisting of the cross-linked cationic polymer network were prepared using Pluronic F127 and poly(ethylenimine) (PEI) and folic acid was conjugated to the surface of nanoparticles.Nanoparticles consisting of a cross-linked cationic polymer network were prepared using Pluronic F127 and poly(ethylenimine) (PEI) and suggested as a drug delivery system for the anticancer drug Paclitaxel (PTX). In order to further improve the targeting capability of nanoparticles, folic acid (folate) was conjugated to the surface of nanoparticles. The characteristics were determined by various methods such as FT-IR for drug state in nanoparticles and DLS and TEM for particle size and morphology. The results found that the drug-loading content was increased when folate was connected to the surface of these nanoparticles. In vitro release experiments indicated that the PTX-loaded nanoparticles showed sustained release profiles compared to PTX solution, especially when nanoparticles were modified by folate. The cytotoxicity of PTX-loaded nanoparticles against cancer cell in vitro was remarkably higher than that of free drug and was better when folate, whose receptor was highly expressed in various tumors, was conjugated to the surface of these nanoparticles. The data demonstrated that this carrier-based approach to delivery of cytotoxic drugs may enhance tumor specificity and significantly reduce side effects related to systemic toxicity usually observed during cancer chemotherapy.
Keywords: Nanoparticles; Multifunction; Ligand mediated; Endosomal breakup;

Directing oxidation of cobalt nanoparticles with the capping ligand by Nguyet Doan; Kyösti Kontturi; Christoffer Johans (126-131).
Cobalt nanoparticles capped with long chain carboxylic acids become hollow when oxidized, while particles capped with tridodecylamine remain solid.Display Omitted► Capping ligand type influences oxidation of cobalt nanoparticles. ► Particle size does not influence the oxide layer for cobalt nanoparticles larger than 8 nm. ► Tridodecylamine offers better long term protection against oxidation then carboxylic acids for cobalt nanoparticles. ► Carboxylic acids promotes Kirkendal effect in oxidation of cobalt particles.The oxidation of Co nanoparticles stabilized with various ligands has been studied in an autoclave. Tridodecylamine stabilized Co nanoparticles with different sizes (8 nm, 22 nm and 36 nm) were prepared by thermal decomposition of Co2(CO)8 in dodecane. The oxidation of the particles was studied by introducing oxygen into the autoclave and following the oxygen consumption with a pressure meter. Tridodecylamine capped particles were initially oxidized at a high rate, however, the oxidation layer quickly inhibited further oxidation. The thickness of the oxide layer estimated from the oxygen consumption was 0.8 nm for all three particle sizes showing that the oxidation is size independent in the studied particle size range. The tridodecylamine ligand was exchanged for various long chain carboxylic acids and the oxidation was studied. While the carboxylic acids give a slower initial oxidation rate, the formed oxide layer does not inhibit further oxidation as effectively as in the case of tridodecylamine. TEM studies show that tridodecylamine capping leads to particles with a metal core surrounded by an oxide layer, while particles capped with long chain carboxylic acids form hollow cobalt oxide shells.
Keywords: Cobalt nanoparticles; Capping ligands; Oxidation; Hollow particles; Nanoparticle oxidation; Kirkendal effect; Cabrera–Mott model;

Cesium salts of heteropoly acid immobilized mesoporous silica: An efficient catalyst for acylation of anisole by K.M. Parida; Surjyakanta Rana; Sujata Mallick; Dharitri Rath (132-139).
CsPTA/MCM-41 is an efficient catalyst for the acylation of anisole. The interaction of anhydride molecules with Brønsted acid sites of catalysts generates acylium, which attacks π-electrons of anisole to form methoxyacetophenones.Display Omitted► Cs-PTA/MCM-41 is an efficient, stable and reusable solid acid catalyst. ► This catalyst is most effective towards acylation of anisole reaction. ► 50Cs-PTA/MCM-41 shows high activity and selectivity towards acylation of anisole. ► The catalytic activity decreased with increase in calcinations temperature. ► FTIR confirmed that Keggin structure remains unaltered when supported on MCM-41.A series of Cs salt of phosphotungstic acid (Cs-PTA) supported on MCM-41 (Cs-PTA/MCM-41) was synthesized by a wet impregnation method and thoroughly characterized by using various analytical techniques, viz. X-ray diffraction, UV–Vis diffused reflectance spectroscopy (UV–Vis DRS), nitrogen adsorption desorption, scanning electron microscopy (SEM), Infrared spectra (FTIR), temperature programmed reduction (TPR), and temperature programmed desorption (TPD). The spectroscopic results revealed that Cs-PTA is highly dispersed on a MCM-41 surface. The 50 wt.% Cs-PTA supported on MCM-41 showed remarkable catalytic performance toward acylation of anisole reaction. The catalyst is regenerable by simple calcinations without appreciable loss in catalytic activity.
Keywords: MCM-41; Cs salt phosphotungstic acid; Acylation; Anisole;

A schematic illustration of the formation of polyion complex micelles.Display Omitted► The micelles were prepared in an aqueous milieu. ► Ionic drug was entrapped into the PICMs. ► The PICMs have marked drug release behavior on the water-soluble drug.Stable and narrow distribution polyion complex micelles (PICMs) were prepared in an aqueous milieu through electrostatic interaction between a pair of oppositely charged block copolymers poly(N-vinylpyrrolidone)-block-poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PVP-b-PAMPS) and monomethoxy poly(ethylene glycol)-block-poly(4-vinyl pyridine) (PEG-b-P4VP). The critical aggregate concentration (CAC), hydrodynamic size, and surface morphology of the prepared PICMs were characterized by fluorescence spectroscopy, dynamic light scattering (DLS), and transmission electron microscopy (TEM), respectively. The resulting CAC and the average diameter of the PICMs were about 43 mg/L and 121 nm, indicating high structural stability of micelles and a size favorable for delivery of drug. In addition, the PICMs exhibited good biocompatibility using the MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide) assay with human embryonic kidney (HEK293) cells. All of these features are quite feasible for utilizing the PICMs as a novel intelligent drug delivery system. In order to assess its application in the biomedical area, the model drug folic acid (FA) was loaded into the micelles and the in vitro drug release behavior was investigated. We found that by manipulating the pH value and salt concentration of the release solution, it was possible to control the release rate of FA.
Keywords: Block copolymer; Polyion complex micelles; Self-assembly; Folic acid; Controlled release;

Porphyrin–phospholipid interaction and ring metallation depending on the phospholipid polar head type by Ana P. Ramos; Christiane Pavani; Yassuko Iamamoto; Maria E.D. Zaniquelli (148-154).
Metallation of a hydrophobically modified 5,10,15,20-tetrakis(4-N-tetradecyl-pyridyl) porphyrin occurs in situ of Langmuir monolayers formed with DMPG; the metallation is partial with DMPA and does not occur for DMPC.Display Omitted► Mixed PyP/ phospholipids Langmuir monolayers ► Different phospholipids polar head ► Metallization of the porphyrinic ring takes place depending on the position of the negative charge at the phospholipid polar head and zinc ions accessibilityThe interaction between a hydrophobically modified 5,10,15,20-tetrakis(4-N-tetradecyl-pyridyl) porphyrin and three phospholipids: two negatively charged, DMPA (the sodium salt of dimyristoyl-sn-glycero-phosphatidyl acid) and DMPG (the sodium salt of 1,2-dimyristoyl-sn-glycero-3-[phospho-rac-(1-glycerol)]) and a zwitterionic DMPC (dimyristoyl-sn-glycero-phosphatidylcholine), were studied by means of surface pressure isotherms and spectroscopic methods. The interaction results in partial or total metallation of the porphyrin with zinc ions in the presence of negatively charged phospholipids, as attested by UV–vis and luminescence spectroscopy of the transferred films. In the presence of the zwitterionic phospholipid no insertion of zinc ion in the porphyrin ring is detected. These results are relevant for the understanding of photosensitizer-lipid-carrier binding for use in photodynamic therapy.
Keywords: Phospholipids; Amphiphilic porphyrin; Langmuir monolayers; Photodynamic therapy;

Effect of organic additives on the formation of alkylsiloxane mesophases by Atsushi Shimojima; Mikako Sakurai; Kazuyuki Kuroda; Tatsuya Okubo (155-160).
The organic additives such as 1,3,5-trialkylbenzenes, n-alkanes, and n-alkyl alcohols caused the swelling or phase change of alkylsiloxane mesophases, leading to the structural control of silica-based nanohybrid materials.Display Omitted► Effects of organic additives on alkylsiloxane mesphases are described for the first time. ► Swollen 2D hexagonal phases are formed by adding 1,3,5-trialkylbenzenes and alkanes. ► Pore size control of calcined products can be achieved. ► Lamellar phases are formed by adding alkyl alcohols.The effects of organic additives (1,3,5-trialkylbenzenes, n-alkanes, and n-alkyl alcohols) on the formation of hybrid siloxane–organic mesophases from alkoxylated precursors (C n H2 n +1Si(OSi(OMe)3)3, 1C n , n  = 6, 10, and 16) have been investigated. These precursors become amphiphilic upon hydrolysis of the alkoxy groups, thus forming two-dimensional (2D) hexagonal phase (n  = 6 and 10) and lamellar phase (n  = 16) by evaporation-induced self-assembly followed by polycondensation. The addition of 1,3,5-trialkylbenzenes or n-alkanes to the 1C10 system leads to swollen 2D hexagonal phases, thereby achieving pore-size expansion of the calcined samples from 2.0 nm up to 3.8 nm in diameter. The effect of these organic additives depends largely on the alkyl chain length of 1C n ; the 2D hexagonal structure (n  = 6) undergoes structural disordering, while the lamellar structure (n  = 16) remains unchanged. On the other hand, the addition of alkyl alcohols to the 1C10 system causes a drastic change in the mesostructure from 2D hexagonal to lamellar, which can be attributed to possible interactions between alcohol molecules and silanol groups of hydrolyzed 1C10. These results provide a facile approach to the fine structural control of nanohybrid materials assembled from single siloxane-based molecules.
Keywords: Alkoxysilanes; Amphiphilic molecules; Self-assembly; Silica; Inorganic–organic hybrids; Mesophase;

Gold nanoparticles conjugated to benzoylmercaptoacetyltriglycine and l-cysteine methylester by O. Estévez-Hernández; E.M. Molina-Trinidad; P. Santiago-Jacinto; L. Rendón; E. Reguera (161-167).
UV–Vis spectra were used as primary sensor for the Au@BzMAG3 and Au@CysM composites formation. In BzMAG3 the mercapto group is benzoyl-protected. A quite different behavior for both composites was observed..Display Omitted► Gold nanoparticles conjugated to BzMAG3 ► Gold nanoparticles conjugated to l-cysteine methylester ► Capping agent as a precursor for a radionuclide-organic complex ► Contrast agent for biological imaging.Benzoyl-protected mercaptoacetyltriglycine, a synthetic precursor used in the preparation of Technetium-99 m-mercaptoacetyltriglycine, a radiopharmaceutical for renal tubular function and l-cysteine methylester, a small, non-zwitterionic amino acid derivative, were used as capping agents of gold nanoparticles obtained by borohydride reduction method. The capped gold nanoparticles composites were prepared from aqueous solutions and characterized by UV–Vis, infrared and Raman spectra and Transmission Electron Microscopy images. The presence of the ligands and its different binding mode to the particles as a consequence of the benzoyl-protection of the thiol group in benzoyl-protected mercaptoacetyltriglycine were evidenced from infrared and Raman spectra. The stability on aging in water solution of the formed composites is discussed from the obtained UV–Vis spectra.
Keywords: Gold nanoparticles; Benzoylmercaptoacetyltriglycine; l-cysteine methylester; Capping agents;

A sharp light scattering increase for small (5 nm) gold nanoparticles upon glutathione injection has been observed and attributed to the avalanche ligand-exchange and glutathione-mediated nanoparticle assembly.The interactions of a biomolecule glutathione (GSH) with citrate-capped gold nanoparticles (AuNP) have been investigated to evaluate the viability of a rapid GSH-capture by gold nanoparticle carriers, as a model system for applications ranging from designing nanoparticle-enhanced functional biosensor interfaces to nanomedicine. The measurements, performed using resonance elastic light scattering (RELS) spectroscopy, have shown a strong dependence of GSH-induced scattering cross-section on gold nanoparticle size. A large increase in RELS intensity after injection of GSH, in a short reaction time (τ  = 60 s), has been observed for small AuNP (5 nm dia.) and ascribed to the fast ligand-exchange followed by AuNP assembly. The unexpected non-Langmuirian concentration dependence of scattering intensity for AuNP5nm indicates on a 2D nucleation and growth mechanism of the ligand-exchange process. The ligand-exchange and small nanoparticle ensemble formation followed by relaxation have been observed in long term (10 h) monitoring of GSH–AuNP interactions by RELS. The results of molecular dynamics and quantum mechanical calculations corroborate the mechanism of the formation of hydrogen-bonded GSH-linkages and interparticle interactions and show that the assembly is driven by multiple H-bonding between GSH-capped AuNP and electrostatic zwitterionic interactions. The RELS spectroscopy has been found as a very sensitive tool for studying interparticle interactions. The application of RELS can be expanded to monitor reactivities and assembly of other monolayer-protected metal clusters, especially in very fast processes which cannot be followed by other techniques.
Keywords: Glutathione; Gold nanoparticles; Ligand-exchange; Resonance elastic light scattering spectroscopy; Surface plasmon;

W1/O/W2 double emulsions stabilised by fat crystals – Formulation, stability and salt release by Sarah Frasch-Melnik; Fotios Spyropoulos; Ian T. Norton (178-185).
Double emulsions show good stability against KCl release when W1 crystal shells are smooth (low osmotic pressure gradient), but release salt rapidly when crystals protrude from interface (high (positive) osmotic pressure gradient).Display Omitted► Double emulsions can be produced using only fat crystals (mono- and triglyceride) to stabilise the primary emulsion ► The fat crystals have sintered to form “shells” around the primary W1 aqueous droplets, to give a special form of Pickering stabilisation ► These double emulsions retain their structure and encapsulated salt over the course of at least 6 weeks when the osmotic pressure gradient is matched between the two aqueous phases ► The sintered crystal “shells” were more stable to compressive rather than tensile loading ► Salt release is likely to occur through “cracks” in the “shells” sustained during the secondary emulsification step.Water/oil (W1/O) emulsions containing fat crystals have been incorporated into an aqueous phase containing 1% na-caseinate as emulsifier to create stable water/oil/water (W1/O/W2) double emulsions. The W1/O primary emulsion was stabilised exclusively with monoglyceride and triglyceride crystal “shells”, and contained 30% W1 aqueous phase as well as KCl.The stability of the double emulsions was monitored over the course of 6 weeks. It was found that, providing some salt or sugar were present in the W2 aqueous phase, emulsions retained their double structure – although coalescence between double emulsion globules occurred and creaming was observed. KCl encapsulated in the W1 phase of the primary emulsion was only slowly released to the W2 continuous aqueous phase: 20% within 6 weeks. This release is due to the damage caused to the fat crystal shells during the secondary emulsification step used to create the double emulsion structure.
Keywords: Fat crystals; Double emulsion; Salt release; Sodium caseinate; Encapsulation; Stability; Osmotic pressure;

Tailoring the wettability of polypropylene surfaces with halloysite nanotubes by Mingxian Liu; Zhixin Jia; Fang Liu; Demin Jia; Baochun Guo (186-193).
Superhydrophobic surfaces of polypropylene (PP)/halloysite nanotubes (HNTs) composites were fabricated via solution blending. HNTs can significantly affect the phase separation process, crystallization, surface roughness and wetting properties of PP.Display Omitted► Halloysite nantoube (HNTs) can act as heterogeneous nuclei for polypropylene (PP) ► HNTs can promote the phase separation process of PP from their solutions ► Micro-papilla like hybrid spherulites with nanostructures can be formed on the PP/HNTs composite surfaces ► These roughness PP/HNTs composites surfaces demonstrate superhydrophobicityIn this contribution, halloysite nanotubes (HNTs), a kind of natural hydrophilic nanoclay, are incorporated into polypropylene (PP) for tailoring the surface microstructures of the composites prepared by solution casting. HNTs act as heterogeneous nuclei for PP, which leads to the change of phase separation process during drying of the composites and consequently the microstructures of composite surfaces. Micro-papilla like hybrid spherulites with nanostructures are formed on the PP/HNTs composite surfaces. The rough surfaces demonstrate superhydrophobicity with a maximum water contact angle as nearly 170° and sliding angle of about 2°. The spherulites size, surface roughness, and wetting property of PP can be tuned by HNTs. HNTs can significantly improve the thermal degradation behavior of the composites which is attributed to the well-dispersed HNTs and the improved interfacial interactions by the nucleation effect. The present work provides an alternative routine for preparing polymer superhydrophobic surfaces via tailoring the surface microstructures by adding nanoparticles in a solution process.
Keywords: Superhydrophobic; Polypropylene; Halloysite nanotube; Crystallization; Nanocomposite; Roughness;

Nisin adsorption to polyethylene oxide layers and its resistance to elution in the presence of fibrinogen by Matthew P. Ryder; Karl F. Schilke; Julie A. Auxier; Joseph McGuire; Jennifer A. Neff (194-199).
A layer of pendant PEO loaded with nisin (top). Contact with fibrinogen is accompanied by partial elution and reestablishment of any lost steric repulsive capacity (bottom).Display Omitted► Nisin entrapment occurs within fibrinogen repellent, pendant PEO layers. ► Entrapment within PEO enhances nisin resistance to elution. ► Sequential adsorption results suggest retention of PEO steric repulsive character.The adsorption and elution of the antimicrobial peptide nisin at silanized silica surfaces coated to present pendant polyethylene oxide chains was detected in situ by zeta potential measurements. Silica microspheres were treated with trichlorovinylsilane to introduce hydrophobic vinyl groups, followed by self assembly of the polyethylene oxide–polypropylene oxide–polyethylene oxide (PEO–PPO–PEO) triblock surfactant Pluronic® F108, or an F108 derivative with nitrilotriacetic acid end groups. Triblock-coated microspheres were γ-irradiated to covalently stabilize the PPO-surface association. PEO layer stability was evaluated by triblock resistance to elution by SDS, and layer uniformity was evaluated by fibrinogen repulsion. Introduction of nisin to uncoated or triblock-coated microspheres produced a significant positive change in surface charge (zeta potential) as a result of adsorption of the cationic peptide. In sequential adsorption experiments, the introduction of fibrinogen to nisin-loaded triblock layers caused a decrease in zeta potential that was consistent with partial elution of nisin and/or preferential location of fibrinogen at the interface. This change was substantially more pronounced for uncoated than triblock-coated silica, indicating that the PEO layer offers enhanced resistance to nisin elution.
Keywords: Nisin adsorption; Zeta potential; Pluronic® F108; PEO–PPO–PEO triblock surfactant; EGAP-NTA;

Helix – Rod transition in a nanospring by Janaky Narayanan; C. Manohar (200-204).
For a given B (measure of attractive van der Waals interaction), nanospring phase is present below a critical surface potential ψc and extended rod-like phase is present above ψc .Display Omitted► Viscosity jump in catanionic surfactant solutions. ► Threshold electric potential for helix - rod transition. ► Effect of refractive index matching on cationic-anionic surfactant mixture.A model of helical spring is described whose effective pitch and length are decided by the balance of the attractive van der Waals and repulsive hydration and electrical double layer forces. Also the electric contribution to the curvature free energy is taken into account. The stability of the nanospring is investigated and it is shown that the spring becomes unstable and jumps to its extended state on increase of electrostatic repulsion beyond a limit implying a jump in viscosity of suspension of springs in the solution. The magnitude of the jump and threshold potential are investigated.
Keywords: Nanospring; Electrical double layer forces; van der Waals interaction; Viscosity; Worm-like micelles; Catanionic surfactants;

Fluorosurfactants for microdroplets: Interfacial tension analysis by Daniel J. Holt; Richard J. Payne; Wing Ying Chow; Chris Abell (205-211).
Quantitative analysis of potential fluorosurfactant candidates and their use in formation of stable aqueous microdroplets in microfluidic environments.Display Omitted► Performance of 12 novel fluorous surfactants quantified. ► Six compounds lower interfacial tension of aqueous-fluorous oil system to below 10 mN/m. ► A number of these compounds effective in producing stable aqueous microdroplets in fluorous oils.Quantitative analysis of a number of potential fluorous surfactants, prepared with a view to stabilisation of microdroplets in microfluidic systems is presented. The surfactants tested comprised compounds with both perfluoropolyether (PFPE) and perfluoroalkyl (PFA) tails, along with three classes of hydrophilic head group, including crown ethers and hexaethylene gylcol. Surfactants were tested for activity using the pendant drop technique. Six compounds proved highly effective and efficient surfactants, with γ CMC  < 10 mN/m and CMCs in the sub-millimolar range. These six compounds stabilised aqueous microdroplets in fluorous oils within poly(dimethylsiloxane) (PDMS) microdevices to a greater degree than commonly used pseudosurfactants such as perfluorooctanol.
Keywords: Fluorosurfactant; Microdroplet; CMC; Pendant drop;

Influence of polymer–surfactant interactions on the reactivity of the CoIII–FeII redox couple by Tapas Majumdar; Harasit Kumar Mandal; Pabitra Kamila; Ambikesh Mahapatra (212-219).
With gradual addition of surfactant molecules, the concentration of micelles increases and more and more polymer hydrophobic residues are incorporated into the micellar hydrophobic cores (I to II): A kinetic study.Display Omitted► A polymer facilitates the micellization of the surfactant, leading to smaller size of micelles, a lower CMC value of surfactant and lower value of degree of ionization of micelles ► Both the cationic and non-ionic surfactant–polymer systems have catalytic effect on the reaction rate of the reduction of CoIII by FeII ► Effectively two forces, one for coulombic and other for hydrophobic interaction, contribute to the catalytic effect of the polymer–surfactant on the redox reaction ► Catalytic effect of the polymer–surfactant mixed systems on the redox reaction is related to the formation of a reverse micellar region with a decrease of dielectric constant of the water pool of the micelles at higher concentrations of polymerIn continuation of our recent study on the inner sphere electron transfer reduction of the cobalt(III) complex, [CoIII(NH3)5N3]Cl2 by Mohr’s salt (FeII), we have investigated the effect of neutral polymer (poly(ethylene glycol) with relative molecular mass 200, PEG 200)–surfactant (both cationic and non-ionic) mixture on the kinetics of the same reaction using spectrophotometric and conductometric techniques at 298 K. Both the cationic and non-ionic surfactants have undergone interaction with polymer. Experimental consequences reveal that the catalytic effect imposed by the polymer–surfactant complexes causes significant change of the kinetic activities of the reaction. The gradual enhancement and retardation of the rate have been found with gradual addition of PEG 200 and cationic surfactant respectively. An attempt has been taken to rationalize the experimental findings with proper correlation of the reported literature.
Keywords: Reduction; Polymer; Surfactant; Poly(ethylene glycol); n-Cetyltrimethylammonium bromide;

The anionic surfactant, SDS interacts strongly with polymeric micelles of a hydrophobically modified copolymer with a negatively charged surface through hydrophobic association, forming a necklace–bead-structure above the CMC.Display Omitted► The copolymer poly(SAMPS/DA) forms nanosize aggregates in aqueous solution ► Despite similar charge the polymeric nanoparticles interact strongly with SDS ► There is no interaction between free polymer chain and the SDS surfactant ► SDS disrupts the polymeric nanoparticles above a critical concentration ► Above its CMC SDS forms a closed necklace–bead-structure in the copolymer solutionThe formation of micelle-like nanosize aggregates above a critical aggregation concentration (CAC) by a water-soluble, amphiphilic, and statistical copolymer poly(SAMPS/DA) of sodium N-acrylamidomethylpropanesulfonate (SAMPS) and N-dodecylacrylamide (DA) was studied. The structural changes that result from the interactions between the polymeric nanoparticles and sodium dodecylsulfate (SDS), an anionic surfactant, were studied with the aid of surface tension, viscosity, steady-state fluorescence, dynamic light scattering, and transmission electron microscopic techniques. In dilute solution with polymer concentration C p  < CAC, the copolymer does not interact with SDS at concentrations lower than its CMC value. The polymer only binds to SDS micelles to produce polymer-decorated micelles. In polyelectrolyte solutions with C p  > CAC, strong interactions between the polyelectrolyte and SDS were observed even at a very low level of surfactant addition. The interaction is purely hydrophobic in nature. The surfactant monomers bind to the polymer micelles to form smaller spherical aggregates (polymer–SDS complex). When surfactant was added above its saturation concentration, the association complexes are disrupted and only surfactant micelles decorated by polymer chain(s) were observed. The microenvironment of the polymer–SDS complexes was observed to be much less polar than that of neat polymer aggregates and SDS micelles. Also, the internal rigidity of the polymer–SDS complexes was found to be higher than that of the pure polymer or SDS micelles. It was observed that the neat polymer aggregates and polymer-decorated SDS micelles are more stable than the polymer–SDS complexes.
Keywords: Hydrophobically modified polyelectrolyte; Polymer–surfactant interactions; Surface tension; Viscosity; Fluorescence; Light scattering; Microscopy;

Influence of stabilizer systems on the properties and phase behavior of supercooled smectic nanoparticles by Judith Kuntsche; Michel H.J. Koch; Frank Steiniger; Heike Bunjes (229-239).
Supercooled smectic nanoparticles have a mostly non-spherical shape varying from more or less perfectly cylindrical (left) to a more rounded shape (right) in dependence on the stabilizer system.Colloidal dispersions of cholesterol esters in the supercooled smectic state (supercooled smectic nanoparticles) are potential novel carrier systems for poorly water soluble drugs. As the supercooled smectic state is metastable, evaluation of its stability and of parameters influencing it is essential. In the present study, the effect of different emulsifiers on the stability of the supercooled smectic state of cholesteryl myristate (CM) nanoparticles and their crystallization was investigated. Nanoparticles were prepared by high-pressure melt homogenization and characterized by dynamic light scattering (DLS), laser diffraction combined with polarization intensity differential scattering (LD–PIDS), synchrotron radiation small-angle X-ray scattering (SAXS), differential scanning calorimetry (DSC) and transmission electron microscopy (TEM, negative staining and cryo-preparation). The various stabilizers resulted in clear differences in the crystallization behavior of the nanoparticles: stabilizers containing a fatty acid chain in their molecule (e.g. phospholipids, sodium oleate and sucrose monolaurate) induced a multiple crystallization event accompanied by a comparatively high recrystallization tendency. In contrast, the recrystallization tendency of nanoparticles stabilized with polymers (e.g. gelatin polysuccinate, poloxamer, poloxamine, polyvinyl alcohol) and sodium glycocholate was much lower and a single crystallization event was observed. The high stability against recrystallization during storage of smectic nanoparticles stabilized with polysorbate 80 in spite of the presence of a fatty acyl group in the molecule suggests that the polar head group (e.g. polyethylene glycol chains) of the emulsifier may also play a significant role.
Keywords: Lipid nanoparticles; Smectic phase; Supercooling; Stabilizer; Crystallization;

Order of inhibition of BSA–CTAB aggregation by additives is trehalose (1) >sucrose (2) >galactose (3) >mannitol (4) >inositol (5) >glycerol (6).Display Omitted► Sugars and polyols inhibit the aggregation of BSA–CTAB ► Sugars are better inhibitor of aggregation than polyols ► Superior performance of sucrose over mannitol can be attributed to its increased effect on solution viscosity.The kinetics of the aggregation of bovine serum albumin (BSA) in the presence of N-cetyl-N,N,N-trimethyl ammonium bromide (CTAB) was studied by monitoring turbidity as a function of time. BSA–CTAB aggregation exhibits an exponential growth, with a pronounced lag phase and a subsequent rapid growth of the aggregates. On the addition of sugars and polyols to BSA–CTAB solution, there is an increase in the lag time and decrease in the rate constant of growth phase indicating that the inhibitors affect both the pre- and post-nucleation processes. The concentration dependence studies of lag time of BSA–CTAB aggregation in the presence of additives points towards the involvement of more number of monomers in the nucleus/start aggregate. The increase in the stability of BSA in the presence of these additives indicates probable role of activation energy in the aggregation. However, the temperature dependence of lag time of BSA–CTAB aggregation shows that the hindrance to molecular collisions, as indicated by decrease in the pre-exponential factor, due to increased viscosity in the presence of additives is the main factor responsible for their inhibitory action. Similarly, higher viscosity of sucrose makes it a much better inhibitor of the heat and surfactant induced aggregation of BSA–CTAB than mannitol.
Keywords: Aggregation; Bovine serum albumin; CTAB; Inhibitor; Sucrose; Mannitol;

Approximate expression for the potential energy of the double-layer interaction between two parallel ion-penetrable membranes at small separations in an electrolyte solution.Display Omitted► An approximate expression for the interaction energy between ion-penetrable membranes is derived ► Donnan potential plays an essential role in the interaction between ion-penetrable membranes ► A new method of linearization of the Poisson–Boltzmann equation is proposedAn approximate expression for the potential energy of the double-layer interaction between two parallel similar ion-penetrable membranes in a symmetrical electrolyte solution is derived via a linearization method, in which the nonlinear Poisson–Boltzmann equations in the regions inside and outside the membranes are linearized with respect to the deviation of the electric potential from the Donnan potential. This approximation works quite well for small membrane separations h for all values of the density of fixed charges in the membranes (or the Donnan potential) and gives a correct limiting form of the interaction energy (or the interaction force) as h  → 0.
Keywords: Ion-penetrable membrane; Donnan potential; Double-layer interaction; Poisson–Boltzmann equation; Linearization;

Fabrication of honeycomb-patterned polyalkylcyanoacrylate films from monomer solution by breath figures method by Xiaofeng Li; Yang Wang; Liang Zhang; Shuaixia Tan; Xiaolan Yu; Ning Zhao; Guoqiang Chen; Jian Xu (253-259).
Honeycomb-like films were prepared directly from the alkylcyanoacrylate monomer solution via a polymerization involved breath figure method on the hydrophobic polypropylene substrate.Display Omitted► Honeycomb-like PACA films are obtained from monomer solution by BFs method ► Water droplets are used as both templates and the initiators ► Ordered porous structure enhances the cell proliferationsHoneycomb-patterned polyalkylcyanoacrylate (PACA) films were prepared from the chloroform solutions of alkylcyanoacrylate (ACA) by breath figures (BFs) method. Condensed water droplets on the solution surface acted not only as templates to endow the ordered structure but also as initiators to trigger the polymerization of ACA. After the polymerization started, the in situ formed polymer chains self-assembled around the water droplets, structuring PACA film with a hexagonal arrangement of holes. This was the first time that polymerization was introduced to breath figures method. The formation mechanism and the influencing factors, including substrates, relative humidity, and solution concentrations were investigated. Hela cells were cultured on both flat and honeycomb-like PACA films to investigate their application as biomaterials.
Keywords: Poly(ethyl α-cyanoacrylate); Breath figures; Honeycomb-patterned; Monomer solution;

Novel Au–Pd bimetallic core–shell nanocomplex and its catalytic activity modulation by De’an Xiong; Zhe Li; Yingli An; Rujiang Ma; Linqi Shi (260-267).
A new kind of Au/Pd bimetallic nanoparticles were synthesized. The Au and Pd nanoparticles distributed in different layers of the complex and the catalytic activity of the complex can be tuned by changing the mole ratio of the two metallic nanoparticles.A novel kind of polymer supported bimetallic nanocomplex was synthesized by a ‘two-step’ method. In this kind of complex, gold nanoparticles, which were stabilized by the tri-block copolymer chains, acted as the core and the Pd nanoparticles were in the shell. The gold nanoparticles and the Pd nanoparticles were connected by a kind of temperature sensitive polymer, poly(N-isopropylacrylamide) (PNIPAM). The bimetallic nanocomplex exhibited excellent catalytic activities in the reduction reaction, and also, the catalytic activity of the nanocomplex could be easily tuned by changing the weight ratio of two metallic particles. Because of the temperature sensitivity of PNIPAM block, the distance between gold nanoparticles and the Pd nanoparticles could be changed or tuned by changing the temperature of its aqueous solution. This novel property would be widely used in the area of testing and microelectronic devices.
Keywords: Bimetallic nanoparticles; Block copolymer; Temperature sensitive; Catalyst; Modulation;

Polymeric scaffolds for enhanced stability of melanin incorporated in liposomes by Marli L. Moraes; Paulo J. Gomes; Paulo A. Ribeiro; Pedro Vieira; Adilson A. Freitas; Ralf Köhler; Osvaldo N. Oliveira; Maria Raposo (268-274).
Melanin in liposomes (A) and LbL films (B). A much stronger adsorption occurred for the film with immobilized liposomes, denoted by the darker color in PEI/DPPG + melanin.Display Omitted► Liposomes protect the melanin in aqueous solution ► Melanin incorporated into liposome may be immobilizated in layer-by-layer filmsThe use of melanin in bioinspired applications is mostly limited by its poor stability in solid films. This problem has been addressed here by incorporating melanin into dipalmitoyl phosphatidyl glycerol (DPPG) liposomes, which were then immobilized onto a solid substrate as an LbL film. Results from steady-state and time-resolved fluorescence indicated an increased stability for melanin incorporated into DPPG liposomes. If not protected by liposomes, melanin looses completely its fluorescence properties in LbL films. The thickness of the liposome-melanin layer obtained from neutron reflectivity data was 4.1 ± 0.2 nm, consistent with the value estimated for the phospholipid bilayer of the liposomes, an evidence of the collapse of most liposomes. On the other hand, the final roughness indicated that some of the liposomes had their structure preserved. In summary, liposomes were proven excellent for encapsulation, thus providing a suitable environment, closer to the physiological conditions without using organic solvents or high pHs.
Keywords: Melanin; Liposome; Dipalmitoyl phosphatidyl glycerol (DPPG); Layer-by-layer films; Fluorescence; Neutron reflectivity;

Adsorption of delmopinol at the solid/liquid interface – The role of the acid–base equilibrium by Olof Svensson; Tobias Halthur; Torgny Sjödin; Thomas Arnebrant (275-281).
Adsorption of delmopinol hydrochloride on Teflon, titanium and stainless steel investigated by radioactive labeling.Display Omitted► Maxima in the adsorbed amount versus concentration curves are observed below the cmc. ► The maxima suggest the presence of two surface active components. ► The two components responsible for this behavior may be the protonated and non-protonated forms.Delmopinol is a tertiary amine surfactant that is used to counteract dental plaque formation. As it is of interest to understand the interfacial behavior from both fundamental and applied perspectives the adsorption of delmopinol to model surfaces was investigated. Adsorption on Teflon, titanium and stainless steel was studied by radioactive labeling and adsorption on silica was studied by quartz crystal microbalance (QCM), ellipsometry and particle electrophoresis.It was shown that the adsorption of delmopinol was complex and strongly influenced by pH and concentration. Pronounced peak values were detected in the adsorption curves (adsorbed amount versus concentration) exceeding the expected value for a bilayer type of structure. To account for this behavior two surface active component were assumed to be present. Accordingly, the high amounts result from the deposition of the component with lower solubility and the decrease at the critical micelle concentration can be explained by solubilization of this component. Based on data from several experimental methods and the pH dependence of the effect we propose an explanation in which the protonated and non-protonated forms of delmopinol represent the two components. However, it cannot be excluded that the component with the lower solubility could be a compound chemically different from delmopinol in the sample.
Keywords: Delmopinol; Surfactant; Amine; Adsorption; Critical micelle concentration; Radioactive labeling; Quartz crystal microbalance; Ellipsometry; Particle electrophoresis;

Mutual displacement experiments between metal ion species.In this paper, the adsorption selectivity and mechanism of diethylenetriamine (DETA)-functionalized PGMA adsorbent (denoted as P-DETA) toward a number of heavy metal ions, including Cu, Co, Ni, Zn, and Cd ions, were experimentally and analytically examined. Experimental results showed a selective adsorption sequence, based on the adsorption affinity, of Cu > Co > Ni > Zn > Cd ions on P-DETA. X-ray absorption fine structure (XAFS) analysis was used to reveal the adsorption coordination geometry, bond length, and coordination number of each type of metal ion with the DETA group. The analysis indicated that Cu, Ni, and Zn ions formed tetrahedral geometry (fourfold coordination) when adsorbed, while Co ion showed an octahedral geometry (sixfold coordination). However, the coordination geometry for Cd could not be obtained in the analysis due to the lack of reference information. The analysis from EXAFS further confirmed that the ratio of DETA ligand to the adsorbed metal ion was probably 1 for Cu, Ni, or Zn ions, while that ratio was 2 for Co ion. From the stability constant (in the log  K form) for a metal ion–DETA ligand coordination (denoted as ML n , where M indicates a heavy metal ion, and Ln indicates n numbers of ligands involved), a relationship of log  K (CuL) > log  K (CoL2) > log  K (NiL) > log  K (ZnL) > log  K (CdL) is suggested. This sequence is in good correlation with the experimentally derived adsorption selective sequence of Cu > Co > Ni > Zn > Cd ions, indicating that the coordination geometry played an important role in the determination of the adsorption selectivity for heavy metal ions by the polyamine-functionalized adsorbent of P-DETA.
Keywords: DETA; Adsorption; Selective; Heavy metal ion; Coordination; Stability constant;

Hierarchical structured ZSM-5 zeolite of oriented nanorods and its performance in the alkylation of phenol with isopropanol by Deju Wang; Xueli Li; Zhongneng Liu; Yahong Zhang; Zaiku Xie; Yi Tang (290-294).
Hierarchical structured ZSM-5 zeolite of oriented nanorods was prepared by zeolite-seed-assisted hydrothermal synthesis without adding mesoscale template; it presents high catalytic activity and stability for phenol alkylation.Display Omitted► ZSM-5 zeolite of nanorods is synthesized hydrothermally by a seed-assisted method. ► ZSM-5 zeolite of aligned nanorods is formed by the oriented aggregation mechanism. ► ZSM-5 zeolite of nanorods brings benefits to the diffusion in catalytic conversions.Hierarchical structured ZSM-5 zeolite of c-axis-oriented nanorods has been prepared by a zeolite-seed-assisted hydrothermal synthesis method without any type of mesoscale template. The final product has loose aggregation which consists of rod-like nanocrystals with widths of about 20–30 nm, formed by the oriented aggregation model. The nitrogen physisorption suggested that the hierarchical structured ZSM-5 zeolite had higher mesopore volume and external surface area than the sample prepared conventionally. Due to the shortened microporous channel and opening mesopore, the prepared HZSM-5 catalyst presents high catalytic activity and stability for the alkylation of phenol with isopropanol.
Keywords: Hierarchical ZSM-5 zeolite; Nanorods; Alkylation; Phenol; Isopropanol;

Synthesis and characterisation of novel organopalygorskites for removal of p-nitrophenol from aqueous solution: Isothermal studies by Binoy Sarkar; Yunfei Xi; Mallavarapu Megharaj; Gummuluru S.R. Krishnamurti; Ravi Naidu (295-304).
Adsorption of p-nitrophenol by organopalygorskites prepared with 100% CEC dimethyldioctadecylammonium bromide (DP1) and cetylpyridinium chloride (CP1), 200% CEC dimethyldioctadecylammonium bromide (DP2) and cetylpyridinium chloride (CP2) is controlled by multiple mechanisms.Organopalygorskites were synthesised by using dimethyldioctadecylammonium bromide (DMDOA) and cetylpyridinium chloride (CP) with surfactant loadings equivalent to 100% and 200% CEC of the palygorskite. The four organopalygorskites, thus produced, were characterised by Fourier Transform Infrared Spectroscopy (FTIR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and zeta potential measurement. FTIR and TGA data demonstrated that higher surfactant loadings as well as long branched chain DMDOA produced highly ordered surfactant conformation. SEM morphological results showed that the organopalygorskites had less entangled fibres than the unmodified palygorskite. The zeta potential values showed positive charge formation on the organopalygorskites surface when they were synthesised with surfactant loadings equivalent to 200% CEC of the palygorskite. The organopalygorskites were tested for adsorption of p-nitrophenol (PNP) with a special focus on the adsorption isotherms. The adsorption data could be fitted with multiple isothermal models indicating that the adsorption was controlled by multiple mechanisms. Sorbent loading rate, initial pH, temperature and ionic strength might all affect the adsorption process. Also, DMDOA modified organopalygorskites reduced desorption/redispersal of adsorbed PNP back into the environment to a great extent. This study will be helpful in designing palygorskite-based organoclay adsorbents for remediating organic environmental contaminants which are ionic in nature.
Keywords: Organoclay adsorbent; Palygorskite; P-nitrophenol; Adsorption; Adsorption isotherm; Desorption;

Adsorption of copper on Pseudomonas aureofaciens: Protective role of surface exopolysaccharides by A.G. González; L.S. Shirokova; O.S. Pokrovsky; E.E. Emnova; R.E. Martínez; J.M. Santana-Casiano; M. González-Dávila; G.S. Pokrovski (305-314).
Adsorption of Cu(II) on P. aureofaciens cells is diminished by the presence of abundant exopolysaccharides via screening of strongly-binding functional groups of the cell wall.Adsorption of copper on exopolysaccharide (EPS)-rich and (EPS)-poor soil rhizospheric Pseudomonas aureofaciens cells was studied as a function of pH and copper concentration at different exposure time in order to assess the effect of cell exopolysaccharides on parameters of adsorption equilibria. The surface properties of bacteria were investigated as a function of pH and ionic strength using potentiometric acid–base titration and electrophoresis that permitted the assessment of the excess surface proton concentration and zeta-potential of the cells, respectively. For adsorption experiments, wide range of Cu concentration was investigated (0.1–375 μM) in order to probe both weak and strong binding sites at the surface. Experimental results were successively fitted using a Linear Programming Model approach. The groups with pK a of 4.2–4.8 and from 5.2 to 7.2, tentatively assigned as carboxylates and phosphoryl respectively, are the most abundant at the surface and thus essentially contribute to the metal binding. The presence of exopolysaccharides on the surface decreases the amount of copper adsorbed on the bacterial cell wall apparently via screening the underlining functional groups of the cell wall. At the same time, dissolved EPS substances do not contribute to Cu binding in aqueous solution. Results of this study allow quantification of the role played by the surface EPS matrix as a protective barrier for metal adsorption on bacterial cell walls.
Keywords: Bacteria; Exopolysaccharide; Copper; Adsorption; Surface complexation;

Sheindorf-Rebuhn-Sheintuch (SRS) describes the simultaneous adsorption of BY 28 and 4-NP.Display Omitted► Simultaneous adsorption of 4-NP and BY 28 onto a Fe-SMPM. ► Cooperative co-adsorption. ► Extended Freundlich model. ► Sheindorf-Rebuhn-Sheintuch model (SRS) gave acceptable results in the range 0–400 μmol g−1.Sorption properties of an iron surfactant-modified pillared montmorillonite (Fe-SMPM) toward two organic pollutants, basic yellow 28 dye (BY28) and 4-nitrophenol (4-NP), were studied at different pH values in both single component and binary pollutant systems. The pseudo-first-order model fits well with the kinetic data obtained in single component studies and sorption capacities of both BY28 and 4-NP increased with the pH value. A sorption synergetic mechanism was observed in binary systems; 4-nitrophenol adsorption was enhanced by the presence of BY28 in the mixture and increased with dye concentrations. Isotherms were described using the Freundlich model in single component systems and the Sheindorf–Rebhun–Sheintuch (SRS) model, an extended Freundlich model, in binary mixtures systems. Hydrophobic interactions between the surfactant-modified pillared clay and the pollutants were suggested to explain the sorption mechanisms.
Keywords: Iron surfactant-modified pillared montmorillonite (Fe-SMPM); 4-Nitrophenol (4-NP); Basic yellow 28 dye (BY28); Pseudo-first-order kinetic; Freundlich model; Coadsorption; Sheindorf–Rebhun–Sheintuch (SRS) model;

Hydroxyaluminum–montmorillonites are common in acidic soils and sediments. Selenite adsorption bond strength decreased with increasing surface coverage. Selenite desorption by various desorbing agents followed the order: Citrate ⩾ Phosphate > Nitrate.Display Omitted► Different extents of surface coverage by preadsorbed selenite (Se) on the hydroxyaluminum-montmorillonite (HyA-Mt) complex showed a substantial alteration of the subsequent Se desorption behavior from the complex. ► The bond strength of Se adsorption on the HyA-Mt appears to be progressively weaker with increasing surface coverage as revealed by larger mole fraction of Se desorption and faster desorption kinetics with higher levels of surface coverage. ► Citrate and phosphate caused much faster Se desorption from the HyA-Mt than nitrate at any given level of surface coverage. ► The findings are of fundamental significance to better understand the consequences of different levels of surface coverage on soil colloids by preadsorbed Se as well as the impacts of phosphate fertilization and rhizospheric processes on the mobility and fate of selenite in soil and related environments.Information on the desorption of metals and metalloids from soils and clays are essential for a better understanding of their mobility, transport, and fate in natural environments. We investigated nitrate-, phosphate-, and citrate-induced desorption kinetics of preadsorbed selenite (presented as Se henceforth) from a hydroxyaluminum–montmorillonite (HyA–Mt) complex at three different surface coverages of 8%, 25%, and 69% of its Langmuir predicted adsorption maximum (262.61 mmole kg−1). Generally the mole fraction of preadsorbed Se released after the attainment of desorption equilibrium was significantly higher with increasing surface coverage. Desorption kinetics of Se from the clay was best described by the Elovich model. The Elovich model parameter β representing the rate of Se desorption increased as the surface coverage increased. Both kinetic data and mole fraction of Se released at desorption equilibrium supported the contention that adsorption bond strength progressively decreases with increasing surface coverage. Both citrate and phosphate remobilized Se at significantly faster rates than nitrate at any surface coverage level. Citrate showed a significantly faster rate of Se release than phosphate only at 8% surface coverage but not at 25% and 69% surface coverages, suggesting that differential ability of these two ligands to influence the kinetics of Se release was also surface coverage dependant. The findings of the present study would help better understand the consequences of different surface coverages on soil colloids by preadsorbed Se as well as the impacts of phosphate fertilization and rhizospheric processes in influencing Se mobility in soil and related environments.
Keywords: Selenite; Surface coverage; Adsorption; Desorption; Kinetics; Hydroxyaluminum; Montmorillonite;

Adsorption of pyrantel pamoate on mercury from aqueous solutions: Studies by stripping voltammetry by Vinod K. Gupta; Rajeev Jain; N. Jadon; K. Radhapyari (330-335).
Cyclic voltammetry of pyrantel pamoate after pre-concentration.Display Omitted► The method has distinct advantages over other existing methods in terms of sensitivity, time saving and delectability. ► Can be applied to the detection of pyrantel in different pharmaceutical dosage forms. ► No sophisticated instrumentation is required. ► Good analytical alternative in comparison to spectrophotometric and chromatographic methods for determining pyrantel pamoate. ► Can be adopted for pharmacokinetic studies as well as for quality control in pharmaceutical laboratories.Adsorption and electrochemical reduction of pyrantel pamoate are studied in Britton Robinson buffer medium at hanging mercury drop electrode (HMDE) by Adsorptive Stripping Voltammetric technique. The peak current shows a linear dependence with the drug concentration over the range 250 ng mL−1 to 64 μg mL−1. Applicability to assay the drug in urine samples is illustrated in the concentration range 5–20 μg mL−1.
Keywords: Pyrantel pamoate; Dosage form; Biological fluids; Adsorptive stripping voltammetric techniques; Hanging mercury electrode;

Dynamics of the cavity and the surface film for impingements of single drops on liquid films of various thicknesses by Nils Paul van Hinsberg; Mete Budakli; Sebastian Göhler; Edin Berberović; Ilia V. Roisman; Tatiana Gambaryan-Roisman; Cameron Tropea; Peter Stephan (336-343).
Experimental and numerical investigation of single drop impact onto liquid wall films of finite thickness. The dynamics of the film height between the cavity and the solid wall are monitored in time, leading to a clear relation between the residual wall film thickness and the Reynolds number of the impacting drop.This paper presents experimental and numerical investigations of single drop impacts onto liquid films of finite thickness. The dynamics of the drop impingement on liquid surface films, the shape of the cavity, the surface film dynamics and the residual film thickness are investigated and analysed. The shape of the penetrating cavity within the surface film is observed experimentally using a high-speed video system. Additionally, the thickness of the liquid film between the expanding, receding and retracting cavity and the solid wall is monitored in time using an optical sensor based on chromatic confocal imaging. The effects of various influencing parameters, such as the drop impingement velocity, liquid properties (surface tension and viscosity) and the initial liquid film thickness, on the time evolution of the cavity and film dynamics are investigated. Complementary to the experiments direct numerical simulations of the drop impacts and cavity expansion are performed using a volume-of-fluid free-surface capturing model in the framework of the finite volume numerical method. The numerical predictions of the film thickness dynamics agree well with the experiments for most phases of the impingement process. Finally, a scaling analysis of the residual film thickness between the cavity and the solid wall is performed for various impingement parameters.
Keywords: Single drop impingement; Residual film thickness; Confocal chromatic sensor; Cavity propagation;

Biomimetic hierarchical ZnO structure with superhydrophobic and antireflective properties by Junjie Xiong; Sachindra Nath Das; Beomki Shin; Jyoti Prakash Kar; Ji Hyuk Choi; Jae-Min Myoung (344-347).
A two step method creates ZnO hierarchical structure mimicking the lotus leaf surface, which shows high water contact angle.Display Omitted► Simple method to develop ZnO based lotus-like structures without using lithography. ► High water contact angle (>160°) with a low contact angle hysteresis (2°). ► Low reflection over a wide spectral range. ► Potential applications in many industrial fields, e.g., self-cleaning, solar cells, displays.A two step method, with a combination of top-down and bottom-up approaches, was developed for the fabrication of ZnO based hierarchical structures with nanorods on microcraters. A layer of well c-axis aligned, transparent, conductive ZnO thin film was deposited by pulsed DC sputtering on a Corning glass substrate. The microcraters were created with anisotropic etching on the as-deposited ZnO thin film. ZnO nanorods were then synthesized onto the etched film by means of metal organic chemical vapor deposition. The resulting hierarchical film exhibits a high water contact angle (>160°) with a low contact angle hysteresis (2°) and low reflection over a wide spectral range. This biomimetic material may find potential applications in many industrial fields, e.g., self-cleaning, solar cells, displays.
Keywords: ZnO; Hierarchical nanostructure; Antireflection; Superhydrophobic; Self-cleaning;

Desorption resistance of bound polycyclic aromatic hydrocarbons may exist in dissolved humic acid.Display Omitted► The magnitude of partitioning coefficients of PAHs in humic substances (HS) correlated strongly with the O/C atomic ratio and molecular weight of HS ► A proposed model for quantification of desorption reversibility of HOCs in dissolved HS ► The PAHs with lower K OW values desorbed almost reversibly from an aquatic fulvic acid, a sediment humic acid (HA), a lignite HA and Aldrich HA However for strong hydrophobic chrysene binding to the lignite HA, some extent of desorption resistance was found that could be attributed to sorption hysteresis as well as steric hindrance ► The aggregation and conformational behavior of HS.Binding of hydrophobic organic compounds (HOCs) to humic substances (HS) has significant influence on their fate and bioavailability in an aquatic environment, yet very little is known on the desorption behavior of HOCs in dissolved HS. In this study, triolein-embedded cellulose acetate membranes (TECAMs) were used as passive samplers in dissolved HS-containing solutions to extract the free polycyclic aromatic hydrocarbons (PAHs). The partitioning coefficients (K OC) of PAHs in dissolved HS from different sources were determined. Then the rapidly desorbable fractions (f rd) of HOCs in dissolved HS were quantified by a quasi-equilibrium model. Results show that the magnitude of K OC of PAHs correlated strongly with the O/C atomic ratio and molecular weight of HS. The PAHs with lower K OW values desorbed almost reversibly from an aquatic fulvic acid, a sediment humic acid (HA), a lignite HA, and Aldrich HA. However, for strongly hydrophobic chrysene binding to the lignite HA, some extent of desorption resistance was found and attributed to sorption hysteresis as well as steric hindrance. The present study illustrated that the quality of HS and the property of solute may play key roles in determining the desorption reversibility.
Keywords: Dissolved humic substances; Polycyclic aromatic hydrocarbons; Sorption and desorption reversibility; Freely dissolved concentration;

Dynamic sorption curves for typical gasoline components in membranes: thiophene has higher sorption and permeation coefficients than hydrocarbons, which is key in fulfilling the separation of thiophene/hydrocarbon mixtures.Display Omitted► Zeolite filling promotes permeation of small molecules in membrane. ► Higher sorption speed of thiophene than hydrocarbons is the key on their separation. ► Trade-off phenomenon exists for PEG/CuY hybrid desulphurization membranes.Polyethylene glycol (PEG)–CuY zeolite hybrid membranes were prepared for sulfur removal from gasoline feed. The sorption and diffusion behavior of typical gasoline components through the hybrid membranes has been investigated by systematic studies of dynamic sorption curves. Influencing factors including feed temperature, permeate pressure, and zeolite content in the membranes on membrane performance have been evaluated. Immersion experiments results showed the preferential sorption of thiophene, which is key in fulfilling the separation of thiophene/hydrocarbon mixtures. The sorption, diffusion, and permeation coefficients of gasoline components in filled membranes are higher than those in unfilled membranes. Pervaporation (PV) and gas chromatography (GC) experiments results corresponded to the discussions on dynamic sorption curves. PV experiments showed that lower permeate pressure meant higher separation performance. The optimum temperature occurred at 383 K, and an Arrhenius relationship existed between permeation flux and operating temperature. The CuY zeolite filling led to a significant increase of flux since the porous zeolite provides for more diffusion for small molecules in mixed matrix membranes. The sulfur enrichment factor increased first and then decreased with the increasing zeolite content, which was attributed to the combined influence of complexation force between CuY and thiophenes as well as the trade-off phenomenon between flux and selectivity. At 9 wt% CuY content, a higher permeation flux (3.19 kg/(m2  h)) and sulfur enrichment factor (2.95) were obtained with 1190 μg/g sulfur content level in gasoline feed.
Keywords: Zeolite; Thiophene; Pervaporation; Hybrid membrane; Desulfurization;

Electrophoresis of surfactant-free bubbles by J.F. Harper (361-367).
Surface charge q E from a new theory for gas-bubble electrophoresis and Kelsall et al.’s experiments. ×, size ∝ bubble diameter: individual bubble results. Circles: mean q E for each pH.In 1996 Kelsall et al. reported electrophoretic experiments with oxygen bubbles in dilute solutions of several salts that were remarkably free of surfactants, but the experimental results agree with neither their own theory nor anyone else’s known to the present author. This paper assumes a double-layer thickness much smaller than the bubble radius, as it was in the experiments. It redevelops the theory on various hypotheses about the precise location of the free surface charge, and both with and without van der Weg’s recently-suggested modification to the electrochemical potential. The results suggest that the free surface charge is at or on the gas side of the change in permittivity at a bubble’s surface in a surfactant-free liquid, and that the classical theory for the speed of rise of a bubble is not quite correct in an electrolyte solution, but the correction is too small to measure. However, there are still unresolved difficulties with both theory and experiments, which van der Weg’s suggestion does not remove. Nor does it improve the fit between theory and Grahame’s experiments on the differential capacitance of a double layer.
Keywords: Electrophoresis; Bubble; Gouy–Chapman; van der Weg;

Emulsions-directed assembly of gold nanoparticles to molecularly-linked and size-controlled spherical aggregates by Irshad Hussain; Haifei Zhang; Mathias Brust; Justas Barauskas; Andrew I. Cooper (368-372).
Size-controlled spherical assemblies of gold nanoparticles are formed by confining them in oil-in-water emulsions of controlled sizes followed by their cross-linking with alkanedithiols.Display Omitted► Oil-in-water emulsions used to produce spherical gold nanoparticle assemblies. ► The amount of gold nanoparticles in oil droplets limit the size of their assemblies. ► Controlling the size-distribution of oil droplets controls the uniformity of nanoparticle assemblies.Aggregation of gold nanoparticles into soluble spherical assemblies using bi-functional ligands i.e., dithiols has recently been demonstrated but with limited control over the size of such assemblies. Herein, we report a new approach to further control the size of water dispersible spherical assemblies by confining gold nanoparticles in tiny oil droplets in water (oil-in-water emulsions) followed by their cross-linking with alkanedithiols. By controlling the size of the oil droplets and the concentration of nanoparticles, the size of spherical aggregates can be controlled from 20 to 400 nm. Cryo-TEM micrographs confirm the formation of covalently-linked soluble spherical nanoparticle assemblies within the oil emulsions in water. Such size-controlled nanoparticle assemblies may have several potential applications including those in gas sensors, controlled delivery, and optical coatings.
Keywords: Gold nanoparticles; Emulsions-directed assembly; Porous nanospheres;

Impact of drops on the surface of immiscible liquids by Ehsan Yakhshi-Tafti; Hyoung J. Cho; Ranganathan Kumar (373-376).
Drops released on the free surface of an immiscible liquid usually form a partially-submerged lens structure. In addition to this configuration, it is shown that a drop released from a range of critical heights can sustain the impact and at the end maintain a spherical ball-shape above the surface despite undergoing large deformation. This spherical configuration of drops at the air–liquid interface is metastable and transforms into the stable submerged lens-shape in a fraction of a second.Display Omitted► Low speed impact of water drops on the surface of fluorocarbon liquid is investigated. ► In addition to the familiar lens configuration, drops released from critical heights can sustain the impact and form a spherical ball-shape structure above the surface. ► Transition of metastable spherical drops into a stable lens configuration at the interface is studied.Impact of drops on the surface of an immiscible liquid is studied. We show that in addition to the commonly-observed lens structure at the air–liquid interface, drops released from critical heights above the target liquid can sustain the impact and at the end maintain a spherical ball-shape configuration above the surface despite undergoing large deformation. The existence of this metastable state of the drop above the free surface and its transition into the more stable submerged lens configuration at the air–liquid interface is investigated. The initial impact which induces the degree of submergence is critically related to the two distinct life paths of drops impinging upon a liquid surface.
Keywords: Drop impact on immiscible liquids; Free surface; Drop shape;

Three-dimensional electrokinetic particle focusing in a rectangular microchannel by Litao Liang; Shizhi Qian; Xiangchun Xuan (377-379).
Neutrally buoyant particles in electrophoresis through a rectangular microchannel travel in a focused stream along the channel axis as a result of the wall-induced lateral migration.Display Omitted► Particles in electrophoresis are three-dimensionally focused. ► Wall-induced electrical force generates the particle focusing. ► Focusing increases with channel length, particle size, and electric field.We extend an earlier study (Liang et al., 2010 ) to demonstrate a three-dimensional focusing of neutrally buoyant particles in electrophoresis through a rectangular microchannel as a result of the wall-induced lateral migration.
Keywords: Particle focusing; Electrokinetic; Dielectrophoresis; Microfluidics;