Journal of Colloid And Interface Science (v.348, #1)

Cover 1 (OFC).

Antibodies against human IgG were immobilised onto gold surfaces and gold particles, both embedded in a lipoate-terminated TRIS-acrylamide polymer to yield highly effective immunosensors on polystyrene and gold.Colloidal gold has been used as a label in sandwich assays for human IgG, in which intercalating N-[tris(hydroxymethyl)methyl]acrylamide (pTHMMAA) polymers have been employed to stabilise the particles coated with antibody fragments. A direct absorbance reading of the particles could be obtained from sandwich assays on polystyrene, and a strongly amplified response was observed in similar assays based on Surface Plasmon Resonance (SPR): for h-IgG, detection limits below 100 pg/mL could be achieved. Three different polymer lengths and two different particles sizes were compared in sandwich assays performed on polystyrene and gold. The resulting binding curves fitted well to the Langmuir–Freundlich isotherm and the binding constants were in good agreement with the values found in earlier studies. The amplification afforded by the nanoparticles was strongly dependent on the antigen concentration, on the type of polymer and on the particle size. Compared to the direct response of the antigen, amplification factors larger than 100 could be achieved. The study proves that the polymers give stabilised particles, which can be used in highly sensitive sandwich assays.
Keywords: Colloidal gold; Antibody Fab′-fragment; Immobilisation; Stability; Surface Plasmon Resonance; Sandwich immunoassay;

PNIPAM adsorbs as individual molecules at 25 °C. Upon heating to 50 °C, phase separation and additional polymer deposition causes aggregation. PNIPAM molecules added at 50 °C self-associate before they can deposit onto the surface, resulting in little aggregation.The effects of temperature and molecular weight of the temperature-responsive polymer, poly(N-isopropylacrylamide) (PNIPAM) were investigated in the solid–liquid separation of silica and alumina mineral particles. Suspensions dosed with PNIPAM at 25 °C were stable and did not settle. When the temperature was raised above the polymer lower critical solution temperature (LCST) (>32 °C), the suspensions were found to have high settling rates, large particle aggregate sizes and high suspension shear yield stresses (τy ). The sediment bed solids volume fraction (ϕf ), of these suspensions was found to increase after a temperature decrease below the polymer LCST and was attributed to a decrease in the attractive particle–particle interactions as shown by a corresponding decrease in shear yield stress, with decreasing temperature. Settling rates were found to increase with molecular weight when suspensions were dosed at 25 °C and settled at 50 °C. Increasing polymer molecular weight resulted in increased molecular polymer adsorption at 25 °C. Greater initial adsorbed amounts of polymer on the surface produced more nucleation sites for deposition of additional polymer as the temperature was increased from 25 °C to above the LCST where polymer phase separation occurred. When the polymer was dosed at 50 °C, the rate of sedimentation was very low. Under these conditions, the polymer molecules associate with each other to form polymer aggregates of typically 1250 nm diameter. These colloidal polymer aggregates do not readily deposit on the particles surfaces such that mineral particle aggregation does not readily occur.
Keywords: Poly(N-isopropylacrylamide); Flocculation; Aggregation; Temperature-responsive polymer; Solid–liquid separations; Polymer adsorption and deposition;

A rapid phase transfer method for nanoparticles using alkylamine stabilizers by Xinnan Wang; Shuping Xu; Ji Zhou; Weiqing Xu (24-28).
The metal nanoparticles can be transferred from aqueous to organic phase using alkylamine as a surface modifier. The phase transfer can occur on short time scales on the order of 30 s.Phase transfer of noble metal nanoparticles (NPs) (>20 nm) from aqueous to organic media is a challenge in colloidal science. We have developed a rapid and simple phase transfer method with alkylamine as the surfactant, through which gold (106 nm in diameter) and silver NPs (118 nm in edge length) can be transferred from aqueous to organic phases. Three alkylamines with different chain-lengths (NH2–(CH2) n−1–CH3, n  = 12, 16 and 18) were compared, and octadecylamine (ODA) was the most efficient. The ODA–NP complex rapidly formed as a result of shaking the mixture of ODA (in ethanol) and NPs (in water). After 20 s, the complex separated from the liquid phase because of their hydrophobicity. The undissolved ODA–NP complex could be redispersed into organic solvents, such as chloroform. Ultraviolet–visible (UV–vis) spectroscopy and transmission electron microscopy (TEM) results show that the metal NPs are still monodisperse having been transferred into organic solvents. The whole process of the phase transfer of NPs from aqueous to organic media can be made to happen in less than 1 min.
Keywords: Phase transfer; Nanoparticle; Metal colloid; Alkylamine; Octadecylamine;

Achieving high-purity colloidal gold nanoprisms and their application as biosensing platforms by Zhirui Guo; Xu Fan; Lianke Liu; Zhiping Bian; Chunrong Gu; Yu Zhang; Ning Gu; Di Yang; Jinan Zhang (29-36).
High-purity colloidal gold nanoprisms (∼97%) were achieved by exploiting the electrostatic aggregation and shape effects through a seed-mediated, iodide ion- and CTABr-assisted synthetic system and used for biosensing in solution.Gold nanoprisms with average edge size of ∼140 nm and thickness of ∼8 nm were achieved in high-purity (∼97%) by exploiting the electrostatic aggregation and shape effects through a modified seed-mediated approach. The proposed strategy lies in the dramatically different stability and aggregation potential between the produced gold nanoprisms and spherical gold nanoparticles, which can be modulated by varying the anion concentration in the reaction solution. Hence, the gold nanoprisms spontaneously aggregated into precipitate whereas most of the spherical ones were still kept in the solution. Moreover, this strategy is also flexible enough that ultra-small gold nanoprisms with average width less than 50 nm can be collected in good-purity. The structure and optical properties of these nanoprisms have been studied by TEM, SAED, XRD and UV–vis–NIR spectroscopy, respectively. These high-purity colloidal gold nanoprisms exhibit remarkably enhanced surface plasmon resonance (SPR) as well as strong near-infrared absorption. Furthermore, we have also investigated their potential for biosensing based on the sensitive changes of SPR band induced by the antibody–antigen recognition events. The experimental results clearly suggest that gold nanoprisms can be a promising nanostructured system for plasmonic sensor applications.
Keywords: Gold; Nanostructure; Electrostatic interaction; Anisotropic shape; Biosensor;

The ZnPc micro-rectangular tubes with hollow interior space are built from densely nanosheets showing super-hydrophobicity and high visible photocatalytic property.A novel zinc phthalocyanine (ZnPc) hierarchical nanostructure with hollow interior space has been successfully obtained by a facile ethylene glycol solvent–thermal synthetic route. The as-obtained products were characterized by field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), IR spectrum, UV–vis spectrum, Brunauer–Emmett–Teller analysis and contact angle measurement. It was indicated that the ZnPc micro-rectangular tubes with hollow interior space were built from densely nanosheets with a thickness of about 20 nm. The obtained ZnPc showed high visible photocatalytic property to degrade rhodamine B (RB), which could be ascribed to the contribution of hierarchical nanostructure, high crystallinity and super-hydrophobic property.
Keywords: Phthalocyanine; Hierarchical nanostructure; Super-hydrophobicity; Photocatalysis;

Rutile TiO2 inverse opal with photonic bandgap in the UV–visible range by Yu Li; François Piret; Timothée Léonard; Bao-Lian Su (43-48).
Highly organized, dense and highly thermal stable rutile Titania inverse opal-based photonic crystals that exhibit intense reflective properties in the UV–Visible range have been constructed by an efficient scientific strategy and possesses a complete photonic bandgap due to the highly refringent dense rutile phase and the controlled and small lattice parameters of the crystal.Highly organized rutile Titania inverse opal-based photonic crystals that exhibit reflective properties in the UV–Visible range have been constructed. A self-assembly method was employed to infiltrate the interstitial space of a highly organized polymeric opal with a titania alkoxide precursor under well controlled conditions. Further hydrolysis and drying steps led to the formation of polystyrene spheres/amorphous TiO2 opaline nanocomposites which exhibited very interesting optical properties with a photonic bandgap (PBG) in the infrared range. The TiO2 inverted opal was subsequently obtained by the removal of the template either by chemical dissolution or calcination. The latter method was shown to yield samples of high quality and the influence of the calcination temperature on photonic crystal properties was studied by XRD, FESEM, EDX and Reflectance measurements. The highly organized, dense and thermally stable TiO2 inverse opal obtained through calcination shows low defect density and a sharp reflection of incident UV–Vis–NIR light at around 380 nm and is then expected to possess a complete photonic bandgap due to the highly refringent dense rutile phase and the controlled and small lattice parameters of the crystal. The crystalline phase, the structural properties and the excellent thermal stability of the material (up to 1000 °C) are discussed.
Keywords: Rutile; TiO2; Inverse opal; Photonic bandgap; Photonic crystal; PS colloids;

Preparing chelated copolymer membrane for fabrication of Ag dendrites by Wei-Ming Cheng; Cheng-Chien Wang; Chuh-Yung Chen (49-56).
The chelated copolymer membrane (PBAGI membrane) functions as a template for growing Ag dendrites with assistance of PVP moleculesA novel method to prepare Ag dendrites on the surface of polymer membranes, which was synthesized by using the soap-free emulsion copolymerization of n-butylacrylate (BA) and acrylonitrile (AN), as well as 2-methacrylic acid 3-(bis-carboxymethylamino)-2-hydroxy-propyl ester (GMA–IDA) that was used as a chelating group, is presented in this study. The characteristics of polymer membranes were investigated by Fourier transform infrared (FT-IR) spectroscopy and elementary analysis (EA). The weight fraction of the chelating group (GMA–IDA) in the polymer was 4.2% as revealed by elemental analysis. The chelating group, –N(CH2COONa+)2 on the polymer was used to coordinate nickel(II) ions, whose chelating amount was estimated by an atomic absorption spectrophotometer (AA). The coordinated Ni2+ ions were subsequently reduced to nickel nanoparticles, which functioned as templates for growing Ag dendrites from aqueous solution of Ag+/poly(vinyl pyrrolidone) (PVP) aqueous solution. The phase identification of the Ag dendrites was confirmed by X-ray diffraction (XRD). Scanning electronic microscopy (SEM) showed the averaged dimension of Ag dendrites was about 2–3 μm in length and ca. 100 nm in diameter. Moreover, the amount of Ag dendrites increased with the decreasing PVP concentration present in the aqueous solution. The energy dispersive X-ray spectrometer (EDX) reveals that the formation of the Ag dendrites was chiefly through the redox reaction of nickel nanoparticles and Ag+ ions, namely galvanic reaction.
Keywords: Ag dendrite; Chelating copolymer membrane; Poly(vinyl pyrrolidone); Galvanic reaction;

Preparation of silica sphere with porous structure in supercritical carbon dioxide by Maya Chatterjee; Abhijit Chatterjee; Yutaka Ikushima; Hajime Kawanami; Takayuki Ishizaka; Masahiro Sato; Toshishige Suzuki; Toshirou Yokoyama (57-64).
Silica sphere with porous structure has been fabricated in supercritical carbon dioxide by the delicate CO2 trapping phenomenon intended for void formation in the inorganic framework.Silica sphere with porous structure has been synthesized in supercritical carbon dioxide. The structure originates from a delicate CO2 trapping phenomenon intended for void formation in the inorganic framework. Silicate polymerization and subsequent removal of CO2 by depressurization leaves the porous architecture. The key factor to obtain stable porous spherical structure was CO2 pressure. Different characterization techniques such as X-ray diffraction, scanning and transmission electron microscopy and N2 adsorption–desorption isotherm were used to determine the framework structure, morphology and porosity of the material. Microscopic visualization of calcined material suggested that the spherical structure was consisted of macroporous windows of diameter ∼100 nm and the space between macropores presents a wormhole like mesoporous/microporous structure. The pore diameter of the mesoporous structure has been calculated as ∼3 nm. X-ray diffraction and N2 adsorption isotherm analysis confirmed the presence of micropores and also the macropores. In addition, the resulting material possess high thermal and hydrothermal stability associated with fully SiO4 cross-linking. The spherical structure with different types of porosity was successfully obtained without using any molding agent.
Keywords: Porous structure; Silica sphere; Supercritical carbon dioxide; Molecular modeling;

Synthesis and characterisation of ferrihydrite/silica co-precipitates by Laurence Dyer; Phillip D. Fawell; O.M.G. Newman; William R. Richmond (65-70).
Ferrihydrite/silica co-precipitates imaged by EFTEM. Iron distribution matches the thickness profile of the aggregate, but the silica distribution is consistent with a covering of silica on the surface.The effect of the presence of soluble silicates on ferrihydrite precipitation and some properties of the products formed in co-precipitation of ferrihydrite and silica have been investigated. The co-precipitates were formed using a continuous crystallisation process in which a combined iron/silicon feed solution was reacted with sodium hydroxide at a constant rate, while maintaining pH at 2.65 and temperature at 85 °C. The products of co-precipitation and the supernatant solutions were characterised using a variety of analytical techniques including X-ray diffraction (XRD), transmission electron microscopy (TEM) and surface charge measurements. The addition of silicates was shown to have a significant impact on the crystallinity and surface charge of the precipitates formed. For products collected after five residence times in the continuous crystalliser, co-precipitates formed from ferric sulfate solution were found to contain considerably less silica than those formed from ferric nitrate. We conclude that adsorption of silicate species on ferrihydrite surfaces speeds up the polymerisation process, and that sulfate ion competes with silicate for surface adsorption sites. Thus, the precipitation of silica proceeds much more rapidly in ferric nitrate media, than in ferric sulfate.
Keywords: Ferrihydrite; Silica; Continuous crystallisation; Composite materials;

Photoactive SAM surface for control of cell attachment by Nan Cheng; Xudong Cao (71-79).
Novel photo-cleavable poly(ethylene glycol) covered thiol-gold self-assembled monolayer (SAM) can switch from cell repulsive to cell adhesive by UV-irradiation followed by RGD peptide immobilization.A new approach to control cell attachment using photochemistry and self-assembled monolayers (SAMs) has been developed. Poly(ethylene glycol) (PEG) was introduced onto a gold SAM surface to initially create a cell repulsive surface via a photo-cleavable o-nitrobenzyl functional group. This cell repulsive surface was subsequently rendered cell adhesive by exposure to UV-irradiation which cleaved the photoactive o-nitrobenzyl group, followed by immobilization of cell adhesive peptides to the irradiated regions. Water contact angle measurements, atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) were used to confirm the photoreactions and to characterize surface properties. To study cell attachment on the prepared surfaces, NIH/3T3 fibroblast cells were used. The cell culture results demonstrated that PEG covered SAMs had the ability to repel cells and that the surface became cell adhesive after UV-irradiation to cleave cell non-adhesive PEG from the exposed surface via photo-labile o-nitrobenzyl groups, followed by immobilization of cell adhesive RGD peptides. In this study, we show that cell attachment can be controlled on photo-cleavable PEG–gold SAMs by UV exposure. We also show that the resulting surface is effective to control cell attachment for up to 5 days in culture.
Keywords: SAMs; Photocage; Poly(ethylene glycol); Cell attachment; RGD peptide sequence;

Dispersions of plate-like colloidal particles – Cubatic order? by S. Junaid S. Qazi; Göran Karlsson; Adrian R. Rennie (80-84).
Direct observation of cubatic order in plate-like colloidal dispersions.Experimental evidence for the existence of ‘cubatic’ order in a colloidal dispersion of plate-like particles is presented. In a ‘cubatic’ phase, disk-like particles self-assemble with domains of a few parallel plates and the director tends to be orthogonal in adjacent domains. This phase has been predicted previously by computer simulation. The domains are approximately equiaxial and are predicted to exist only within a limited range of aspect ratios and volume fractions. This locally ordered structure cannot be identified readily using scattering techniques, since the patterns are expected to be similar to those of isotropic liquid phases. For this reason, we have used a real-space technique of cryo-transmission electron microscopy that directly probes such locally ordered structures to study dispersions of nickel hydroxide particles. Polydispersity of particle size is expected to require some local tilting in order to include larger particles in a dense structure and this is discussed with respect to the concentration range for which cubatic order is observed. This new structure offers the possibility of novel materials that could be prepared by self-assembly and have applications in a wide range of fields.
Keywords: Cubatic structure; Plate-like colloids; Cryo-transmission electron microscopy;

Characterizing the surface charge of synthetic nanomembranes by the streaming potential method by Subhra Datta; A.T. Conlisk; Dharmesh M. Kanani; Andrew L. Zydney; William H. Fissell; Shuvo Roy (85-95).
The zeta potential ζapp apparent from streaming potential measurement and thin electric double layer theory is corrected to the true zeta potential value (circle) using finite-EDL streaming potential theory (curve).The inference of the surface charge of polyethylene glycol (PEG)-coated and uncoated silicon membranes with nanoscale pore sizes from streaming potential measurements in the presence of finite electric double layer (EDL) effects is studied theoretically and experimentally. The developed theoretical model for inferring the pore wall surface charge density from streaming potential measurements is applicable to arbitrary pore cross-sectional shapes and accounts for the effect of finite salt concentration on the ionic mobilities and the thickness of the deposited layer of PEG. Theoretical interpretation of the streaming potential data collected from silicon membranes having nanoscale pore sizes, with/without pore wall surface modification with PEG, indicates that finite electric double layer (EDL) effects in the pore-confined electrolyte significantly affect the interpretation of the membrane charge and that surface modification with PEG leads to a reduction in the pore wall surface charge density. The theoretical model is also used to study the relative significance of the following uniquely nanoscale factors affecting the interpretation of streaming potential in moderate to strongly charged pores: altered net charge convection by applied pressure differentials, surface-charge effects on ionic conduction, and electroosmotic convection of charges.
Keywords: Electrokinetic phenomena; Streaming potential; Electrostatic interactions; Electric double layer; Silicon membrane; Polyethylene glycol;

A copper(II) thiosemicarbazone complex built on gold for the immobilization of lipase and laccase by M. Carmen Rodríguez-Argüelles; Reynaldo Villalonga; Carmen Serra; Roberto Cao; M. Angeles Sanromán; María A. Longo (96-100).
A copper(II) complex with imidazole-2-carbaldehyde thiosemicarbazone was built Layer-by-Layer on a gold surface for the immobilization of lipase and laccase.A self-assembled monolayer (SAM) of imidazole-2-carbaldehyde thiosemicarbazone (H2ImTSC) on gold was formed and characterized by ATR-FTIR, Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) and X-ray Photoelectron Spectroscopy (XPS). The self-assembly of the ligand through its thioenolate group was confirmed by ToF-SIMS and the presence of XPS peaks at 161.9 (S2p1/2) and 163.1 eV (S2p3/2). The two nitrogen donor atoms of self-assembled HImTSC were able to coordinate (κ 2-N,N) copper(II) when set to interact with a CuCl2 solution upon a second deprotonation of the ligand. This way, two types of modified gold sheets for the immobilization of lipase and laccase were obtained: (a) SAM of the ligand on gold (Au–HImTSC), and (b) SAM of HImTSC with a second monolayer of copper(II) (Au–ImTSC–Cu(II)). The highest immobilization of enzyme was achieved for laccase on Au–ImTSC–Cu(II) according to XPS and enzymatic activity determinations. Copper(II) played a an important recognition role through coordination to the enzyme and/or electrostatic interactions. Nevertheless, the positively charged surface of Au–ImTSC–Cu(II) affected the activity of laccase.
Keywords: Layer-by-Layer; Self-assembly; Copper(II) complex; Enzyme immobilization;

Effects of natural organic matter on aggregation kinetics of boron nanoparticles in monovalent and divalent electrolytes by Xuyang Liu; Mahmoud Wazne; Yun Han; Christos Christodoulatos; Kristin L. Jasinkiewicz (101-107).
The attachment efficiency kept increasing with the increase of CaCl2 concentration in the presence of alginate. Alginate gel network is responsible for binding of boron nanoparticles.Nano boron is a promising new propellant being considered for military and civilian applications; however, the impact of its release on the environment is largely not known. The early stage aggregation kinetics of boron nanoparticles was investigated in the presence of two kinds of natural organic matter—Suwannee River humic acid (SRHA) and sodium alginate—by dynamic light scattering and transmission electron microscopy (TEM). The addition of SRHA caused the boron nanoparticles to stabilize and resulted in (1) decreased attachment efficiency for the reaction-controlled regime and (2) an increase in the critical coagulation concentration, in CaCl2 and MgCl2 solutions. The increase in the electrostatic repulsion is suggested as a main cause of the induced stabilization as indicated by the electrophoretic mobility measurements. Similar behavior was observed in the presence of alginate and MgCl2. However, the attachment efficiency kept increasing in the presence of CaCl2 and alginate with the increase in the electrolyte concentration and was greater than unity at >4 mM CaCl2. The destabilization was attributed to bridging of the nanoparticles by the alginate–Ca2+ system. Results from this study suggest that various NOM and electrolytes play significant and differing roles in the aggregation of boron nanoparticles in natural aquatic environments.
Keywords: Aggregation; Transport; Nanoparticles; Natural organic matter; Boron; Stabilization; Humic acid; Alginate; DLVO;

Sensitive label-free immunoassay of carcinoembryonic antigen based on Au–TiO2 hybrid nanocomposite film by Yuyong Zhang; Ruo Yuan; Yaqin Chai; Yun Xiang; Xiaoqing Qian; Haixia Zhang (108-113).
The TEM image of Au–TiO2 nanoparticles with large surface-to-volume ratio, film-forming ability, high stability and favorable biocompatibilityIn this paper, a new nanostructured Au–TiO2 particle was synthesised and employed for the construction of a label-free amperometric immunosensor for carcinoembryonic antigen (CEA) determination. The spherical Au–TiO2 nanoparticles provided a good microenvironment for the immobilization of biomolecules, enhanced the surface coverage of protein, had large surface-to-volume ratio, film-forming ability and high stability. The Au–TiO2 nanoparticles were characterized by transmission electron microscopy (TEM). The fabrication process of the electrochemical immunosensor was monitored by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) techniques. Under optimal conditions, the proposed immunosensor exhibits a good linearity at the studied concentration range from 0.2 to 160.0 ng mL−1 towards CEA with a coefficient of 0.9965 and a detection limit of 0.06 ng mL−1 (S/N  = 3). Moreover, the proposed immunosensor shows good selectivity, reproducibility, high sensitivity, and would have a potential application in clinical immunoassays.
Keywords: Au–TiO2 nanoparticles; Nickel hexacyanoferrate nanoparticles; Carcinoembryonic antigen; Amperometric immunosensor;

Novel phosphate-functionalized silica abrasives were prepared using diethylphosphato-ethyltriethoxysilane (DPTS) as the coupling agent. Possible binding of DPTS to both silicon dioxide and silicon nitride surfaces is shown above. These novel abrasives can be used to suppress both silicon dioxide and silicon nitride removal rates to <2 nm/min and simultaneously enhance silicon nitride removal rates to >50 nm/min at pH 5.We prepared and characterized novel phosphate-functionalized silica particles, and showed that, by using them during chemical mechanical polishing, both silicon dioxide and polysilicon removal rates can be suppressed while simultaneously enhancing silicon nitride removal rates. We achieved a silicon nitride:silicon dioxide:polysilicon removal rate selectivity of (>20):1:1. The measured removal rates of silicon dioxide, silicon nitride, and polysilicon are related to the electrostatic interactions and chemical reactivity between these films and the modified-silica abrasives.
Keywords: Silicon dioxide; Silicon nitride; Polysilicon; CMP; Surface functionalization; Electrostatic interactions;

Humic substances promote phase-transfer of hydrophobic organic-capped CdSe quantum dots from hexane to water via coordinating (a) and overcoating (b) mechanisms.Studies of the fate and transport of engineered nanomaterials are invaluable in predicting environmental impact, bioavailability, and toxicity. We report on the influence of humic and fulvic acids (models of natural organic matter) on the phase transfer of organic-capped CdSe quantum dots (QDs) from hexane to water. QDs capped with tri-n-octylphosphine oxide, tetradecylphosphonic acid, and oleic acid, which were otherwise insoluble in water, were transferred into aqueous solutions of humic substances (HS) (Suwannee River humic acid and fulvic acid standards) within 1–10 days after mixing. Phase transfer was characterized by infrared and UV/Vis absorption spectroscopy, emission spectroscopy, dynamic light scattering, electron microscopy, and inductively coupled plasma mass spectrometry. Phase-transferred QDs were intact and temporarily stabilized by HS. On longer timescales, Cd2+ leached into aqueous solution. Our data suggest that two mechanisms promote the phase transfer of QD–HS agglomerates: (1) an overcoating mechanism involving dispersion interactions between non-polar moieties of HS and hydrocarbon chains of organic capping groups and (2) a coordinative mechanism involving displacement of capping groups by Lewis basic functionalities of HS. The structure of the capping group of QDs influenced the relative contributions of the two mechanisms and the extent to which Cd2+ leached into water.
Keywords: Nanomaterials in environment; Quantum dots; Phase transfer; Suwannee River humic and fulvic acids; Environmental stability; Cadmium leaching;

Fluorescein–metallacarborane conjugates interact with a PEO containing double-hydrophilic block copolymer and micelle-like nanoparticles form as a result. The micellar cores contain the PEO blocks with embedded metallacarboranes – potent inhibitors of HIV protease.We prepared nanoparticles differing in morphology from double-hydrophilic block copolymer poly(ethylene oxide)-block-poly(methacrylic acid), PEO–PMA, and two types of fluorescein–[3-cobalt(III) bis(1,2-dicarbollide)] conjugates, GB176 and GB179, in alkaline buffer. GB176 molecule consists of fluorescein attached to the metallacarborane anion. In GB179 molecule, the fluorescein moiety connects two metallacarborane anions. The self-assembly is based on the unusual interaction of metallacarborane clusters with PEO blocks which form insoluble micellar cores. The GB176 containing nanoparticles are loose and irregular, while the GB179 ones are rigid and spherical. The structure of nanoparticles depends to some extent on a procedure of preparation. The micelles were studied by static and dynamic light scattering, fluorometry and atomic force microscopy. Since the metallacarborane conjugates act as potent inhibitors of HIV protease, the presented system is important from the point of view of drug delivery.
Keywords: AFM; Dicarbollide anions; Drug delivery; Fluorometry; Light scattering; Micelles; Nanoparticles; Metallacarboranes; Polymeric composites;

Accelerated decarboxylation of 6-nitrobenzisoxazole-3-carboxylate in imidazolium-based ionic liquids and surfactant ionic liquids by Lucia Brinchi; Raimondo Germani; Elena Braccalenti; Nicoletta Spreti; Matteo Tiecco; Gianfranco Savelli (137-145).
Decarboxylation of 6-NBIC in aqueous solutions of 1-alkyl-3-methylimidazolium derivatives [C n mim][X].We report the use of the unimolecular, spontaneous decarboxylation of 6-nitrobenzisoxazole-3-carboxylate, 6-NBIC, as kinetic probe to investigate the properties of aqueous solutions of a series of ILs, 1-alkyl-3-methyl imidazolium derivatives. The ILs are denoted as [C n mim][X], where n indicates the number of carbon atoms in 1-alkyl chain. We studied [C4mim][X], with X = Cl, Br, and BF 4 - , and the surface-active ILs, SAILs, [C12mim][Cl], [C12mim][Br], and [C16mim][Br]. For comparison purposes we also studied nonmicellizing tetralkylammonium chloride and bromide, denoted as TRAX, where R is alkyl group and X the anion.We observed a steep increase of values of k obs after a certain salt concentration for all the systems used. Electrical conductivity of various aqueous systems was measured, in an attempt to rationalize the kinetic effects. Data from conductivity and kinetic are consistent with the idea that after a certain, high, concentration aggregates of ILs form, and data from the kinetics suggest that water is someway “squeezed out” from these aggregates. As can be deduced from kinetics, properties of the aggregates formed by [C4mim][X] ILs correlate well with bulk water structure affecting properties of the salts, and seem to have no relation to surface effects.
Keywords: Decarboxylation; 6-Nitrobenzisoxazole-3-carboxylate; Imidazolium surfactants; Ionic liquids; Kinetic;

Effect of head groups on the phase transitions in Gibbs adsorption layers at the air–water interface by Md. Mufazzal Hossain; Kenichi Iimura; Masaki Yoshida; Takaya Sakai; Teiji Kato (146-151).
Morphologies of Gibbs monolayers of different amphiphiles at 2 °C.The adsorption kinetics and the surface phase behavior of four different amphiphiles, which are 2-hydroxyethyl laurate (2-HEL), dodecanoyl N-ethanolamide (NHEA-12), dodecanoyl N-methylethanolamide (NMEA-12) and tetradecanoyl N-methylethanolamide (NMEA-14), have been investigated at the air–water interface by film balance, surface tensiometer and Brewster angle microscopy (BAM). The former two amphiphiles show a first-order phase transition from a lower density liquid like phase to a higher density condensed phase in Gibbs adsorption layers. On the other hand, the latter two amphiphiles are unable to show such characteristics under any experimental conditions. The presence of a methyl group in the head group of NMEA-12 sterically hinders the molecules and resists the formation of any condensed phases. This steric hindrance is so high that even an increase in the chain length by two ―CH2 ― groups in NMEA-14 does not allow the formation of condensed domains. Although, both 2-HEL and NHEA-12 are able to form the condensed phase, the domain morphology formed in these monolayers is different from each other. The domains of 2-HEL at lower temperatures are circular having a stripe texture, while those at higher temperatures show fingering patterns having uniform brightness. On the other hand, the domains of NHEA-12 are dendritic in shape. The presence of hydrogen bonding sites close to the interface should be responsible for the formation of such domains in NHEA-12.
Keywords: Gibbs monolayers; Phase transition; Brewster angle microscopy; 2-hydroxyethyl laurate; Dodecanoyl N-ethanolamide; Dodecanoyl N-methylethanolamide; Tetradecanoyl N-methylethanolamide;

Shear-induced structures visualized by light scattering during a thixotropic loop.We present a rheological study for a system made of zwitterionic surfactant N-tetradecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (TDPS), sodium dodecyl sulfate (SDS), and water (0.5 M NaCl). We found that this system forms wormlike micelles. This study is focused in the dilute regime below the overlap concentration, where micelles are not entangled. The overlap concentration was determined using dynamic light scattering. The behavior of the apparent viscosity and the shear stress, both as a function of the shear rate, was determined for different zwitterionic surfactant concentrations, temperatures, and two surfactant ratios (R=[SDS]/[TDPS]). The shear-thickening transition and its temperature dependence was also studied. Finally, we were able to observe the shear-induced structures by using the scattered light from a sheet of light perpendicular to the flow that is installed in the gap of a transparent Couette cell filled with the micellar fluid.
Keywords: Wormlike micelles; Shear thickening; Zwitterionic surfactant; Sulfobetaine;

Surface behavior of a model surfactant: A theoretical simulation study by Shi-Ming Yuan; Hui Yan; Kai Lv; Cheng-Bu Liu; Shi-Ling Yuan (159-166).
Theoretical simulation has been used to calculate the molecular properties of a surfactant SDBS in vacuum and in aqueous solution.A quantum mechanics (QM) method has been used to calculate molecular properties of sodium dodecylbenzenesulfonate (SDBS) in vacuum and in solution. Furthermore, molecular dynamics (MD) simulations have been used to determine the dynamic behavior of SDBS moving from the bulk solution to the air/water interface. QM calculations suggest that two head-group oxygen atoms on each surfactant molecule interact with a Na+ ion, despite the availability of three oxygen atoms in the head group. MD simulations showed that the Na+ ion must overcome the energy barrier between two solvent layers around the head group to form stable ion pair in solution, which is consistent with experimental results. In the simulation, in moving from the bulk to the interface, SDBS can aggregate in a short time, and the adsorption adopts a preferred orientation. The results indicate that formation of favorable hydrophobic interactions of the surfactant alkyl chains is the origin of interfacial adsorption of SDBS.
Keywords: Surfactant; Alkyl benzene sulfonate; Molecular dynamics; Potential of mean force;

Intensity of infrared absorptions (as represented by the peak area of νas(CH2)) are correlated with surface excess of SDS at the α-Fe2O3/aqueous solution interface.Adsorption of sodium dodecyl sulfate (SDS) at the solid/aqueous interface was examined as a function of pH and SDS concentration ([SDS]) using attenuated total reflectance–Fourier transform infrared (ATR–FTIR) spectroscopy and batch uptake experiments. Two types of sorbent surfaces were compared: (i) a hydrophobic zinc selenide (ZnSe) ATR internal reflection element (IRE) and (ii) the same surface coated with hydrophilic nanoparticulate α-Fe2O3 (hematite). The results indicate that adsorption to the ZnSe IRE is affected by both electrostatic attraction and hydrophobic interaction. Batch adsorption and ATR–FTIR spectral results are consistent with SDS forming outer-sphere complexes at the α-Fe2O3 surface. There is also no evidence for ligand (SDS)-promoted dissolution of hematite. Adsorption to hematite is dominated by anion exchange and surfactant self-assembly. ATR–FTIR data indicate that adsorption to both surfaces shows a strong pH dependence at low [SDS] and negligible pH dependence when [SDS] exceeds the critical micelle concentration (cmc). Adsorption to ZnSe IRE shows small variation with [SDS], apparently due to a lack of surfactant self-assembly at the interface. Adsorption to α-Fe2O3 is a rapid process; equilibrium is reached within a few minutes. Conversely, adsorption to the ZnSe IRE shows strong longer time dependence; evidently, hydrophobic interfacial reactions constitute a much slower process.
Keywords: SDS; Adsorption; Hematite; ZnSe IRE; ATR–FTIR spectroscopy;

Electrophoretic mobility of a spherical liposome as a function of ionic strength.The electrophoretic velocity of a spherical liposome with a thin double layer is investigated theoretically for the first time to account for a field-induced redistribution of lipid molecules coupled with ion polarization as well as a capacitive effect when the two leaflets of the bilayer have different surface charges. The formulation also incorporates the influence of water osmotic flow through the bilayer. It is found that the lipid redistribution is stronger for a larger liposome, and can give rise to a smaller electrophoretic mobility. For a sufficiently thin double layer, this effect also increases with increasing strength of the imposed electric field. The capacitive effect is significant for the leaflets having very different charge densities, in particular when the outer leaflet becomes nearly uncharged. For such a case, the induction of a surface potential for the outer leaflet is pronounced, leading to electrophoretic migration of the liposome.
Keywords: Liposome; Vesicle; Phospholipid; Electrophoresis; Charge density; Zeta potential;

Self-assembly in surfactant-based liquid mixtures: Bis(2-ethylhexyl)phosphoric acid/bis(2-ethylhexyl)amine systems by Pietro Calandra; Angela Ruggirello; Andrea Mele; Vincenzo Turco Liveri (183-188).
Schematic representation of the possible local hydrogen-bonded structure of HDEHP/BEEA mixtures leading to the formation of local networks where protons and proton holes can travel by a jumping mechanism.Surfactant-based liquid mixtures constitute an interesting class of nanostructured materials with promising potential in specialized applications. Here, structural and conductometric properties of liquid mixtures composed of bis(2-ethylhexyl)amine (BEEA) and bis(2-ethylhexyl)phosphoric acid (HDEHP) have been thoroughly investigated with the aim to correlate structural features with system charge transport capability. The evolution of self-assembled local nanostructures with system composition has been investigated by FT-IR and XRD while the conductometric properties were probed by conventional AC complex impedance. Both pure components exhibit nano-segregation due to their amphiphilic nature but with only very low proton conductivities. However their mixtures, characterized by local organization of polar and apolar domains driven by acid–base interactions between HDEHP PO4H and BEEA NH groups, show enhanced structural order and proton conductivity.
Keywords: Surfactants; Conducting materials; Self-assembly; Liquid mixtures;

Adsorption characteristics of brush polyelectrolytes on silicon oxynitride revealed by dual polarization interferometry by Goran Bijelic; Alexander Shovsky; Imre Varga; Ricardas Makuska; Per M. Claesson (189-197).
As a result of our investigation we present the illustrations shown in (a–c) describing the structural evolution of the adsorbed layers formed by high charge density PEO45MEMA:METAC-X polymers (50 ⩽  X  ⩽ 75) where the molecules are adsorbed preferentially parallel to the surface. The structural evolution of the layers formed by low charge density PEO45MEMA:METAC-X (10 ⩽  X  ⩽ 25) is illustrated in (d–f). These polymers initially adsorb preferentially parallel to the surface whereas the final layer structure is more extended.Adsorption properties of bottle-brush polyelectrolytes have been investigated using dual polarization interferometry (DPI), which provides real time monitoring of adsorbed layer thickness and refractive index. The adsorption on silicon oxynitride was carried out from aqueous solution with no added inorganic salt, and the adsorbed polyelectrolyte layer was subsequently rinsed with NaCl solutions of increasing concentration. The bottle-brush polyelectrolytes investigated in this study have different ratios of permanent cationic charged segments and uncharged PEO side chains. Both the cationic groups and the PEO side chains have affinity for silica-like surfaces, and thus contribute to the adsorption process that becomes rather complex. Adsorption properties in water, responses to changes in ionic strength of the surrounding medium, adsorption kinetics and the layer structure are all strongly dependent on the ratio between backbone charges and side chains. The results are interpreted in terms of competitive adsorption of segments with different chemical nature. The adsorption kinetics is relatively fast, taking only tens to hundreds of seconds when adsorbed from dilute 100 ppm solutions. The DPI technique was found to be suitable for studying such rapid adsorption processes, including determination of the initial adsorption kinetics. We expect that the effects observed in this study are of general importance for synthetic and biological polymers carrying segments of different nature.
Keywords: Bottle-brush polyelectrolyte; Dual polarization interferometry; Adsorption; Desorption; Adsorption mechanism; Adsorption kinetics; Silicon oxynitride;

Notes on the photo-induced characteristics of transition metal-doped and undoped titanium dioxide thin films by S. Kment; H. Kmentova; P. Kluson; J. Krysa; Z. Hubicka; V. Cirkva; I. Gregora; O. Solcova; L. Jastrabik (198-205).
The photocurrent trend of the Fe-doped TiO2 thin films. These layers tend to create nucleating centers initiating the crystal growth in their close neighborhood.This study reports the preparation of thin nanoparticulate films of titanium dioxide and its modified version doped with a transition metal. The behavior of prepared films was described by means of their photocatalytic and photo-induced electrochemical properties. The TiO2 and M/TiO2 (M = Ag, Zr, Fe) thin films were produced via a standard sol–gel method using titanium n-butoxide, acetylacetone, and transition metal acetylacetonates as precursors. Prepared films were analyzed by a series of techniques involving XRD, Raman spectroscopy, SEM, AFM, and XPS. Their photocatalytic activity was monitored with the aid of decomposition of the model compound Rhodamine B in water. All films were then tested for their photo-induced electrochemical properties based on evaluation of polarization curves (photocurrents). The highest reaction rate constant (0.0101 min−1), which was even higher than that for pure TiO2, was obtained for the Ag/TiO2 sample. The highest quantum yield of the charge collection was determined for the undoped TiO2 film.
Keywords: Sol–gel; Thin layers; Metal-doped TiO2; IPCE; Photocurrent; Photocatalysis;

Fabrication of nanopatterns using block copolymer and controlling surface morphology by Md. Mahbub Alam; Yu-Rim Lee; Jin-Yeol Kim; Woo-Gwang Jung (206-210).
The pore size and shape can be adjusted by controlling the thickness of the film and sonicating the substrate in toluene or acetic acid after UV irradiation.This paper reports an approach for patterning substrates on the nanoscale using a block copolymer, polystyrene-b-polymethylmethacrylate (PS-b-PMMA), which forms cylindrical microdomains. The morphology of the polymer surface was strongly dependent on the thickness of the polymer layer. Spin coating the polymer solution onto the substrate followed by baking resulted in the self-assembly of the components of the polymer. Exposure to ultraviolet radiation degraded the PMMA chain, which could be removed by rinsing in acetic acid to give patterned holes. However, the small size of the hole limits the applications of the template. This problem was solved by sonicating the sample in different solutions in a series of steps to produce a fingerprint pattern or patterns containing PS cylindrical domains having large interstitial spaces with an average of >30 nm. The morphology of the polymer film surface was examined by atomic force microscopy (AFM) and scanning electron microscopy (SEM).
Keywords: Block copolymer; Nanopattern; Thickness; Degradation; Sonication; Fingerprint pattern;

Enhanced photocatalytic degradation of organic pollutants over basic bismuth (III) nitrate/BiVO4 composite by Yuanyuan Liu; Zeyan Wang; Baibiao Huang; Xiaoyang Zhang; Xiaoyan Qin; Ying Dai (211-215).
Basic bismuth (III) nitrate (BBN) and BiVO4 composite show higher photocatalytic activity than BiVO4. The reason is ascribed to the hydroxyl in BBN, which acts as hole trappers.Basic bismuth (III) nitrate (BBN)/BiVO4 composites were prepared by a coprecipitation method. A variety of techniques including X-ray powder diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), diffuse reflectance spectroscopy (DRS), N2 adsorption, and X-ray photoelectron spectroscopy (XPS) were employed to characterize the resulting materials. The composite shows higher photocatalytic activity than BiVO4 over degradation of organic pollutants (RhB, MO, phenol, and 2-propanol). A mechanism was proposed for the enhanced photocatalytic activity. The proposed mechanism was confirmed by experiments with hydroxyl radicals.
Keywords: Photocatalyst; BiVO4; Basic bismuth (III) nitrates; Composite; Hydroxyl;

Comparison of the redox potential of the intercalated ferricyanide species with that of the free species taken in different hydroxyl ion concentrations.Hexacyanoferrate on intercalation within the interlayer region of the layered double hydroxide (LDH) of Mg with Al retains its electroactivity. Within the confined region of the interlayer, the redox potential of the intercalated ion, as estimated from cyclic voltammetric studies, is shifted by almost 126 mV higher than that of the free ion in solution. We attribute this to the activity of hydroxyl ions in the interlayer. By comparing the shifts of the redox potential of the free ion in solutions containing different concentrations of hydroxyl ions, we estimate the concentration of hydroxyl ions in the interlayer to be in the vicinity of ∼11.8 M. This corresponds to 20% of the crystallographically defined number density of hydroxyl ions (equilibrium dissociation constant ∼0.2) and shows that the chemical environment of the interlayer is very similar to that in solution. The LDH of Mg with Al thereby behaves like a strong base.
Keywords: Layered double hydroxide; Hexacyanoferrate; Cyclic voltammetry;

Theoretical simulation of product distributions versus reaction time in the hydrodesulfurization of 4,6-dimethyldibenzothiophene over NiMo sulfide catalyst.The hydrodesulfurization (HDS) of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) over two synthesized unsupported CoMo (CMS) and NiMo (NMS) sulfide catalysts was investigated in a batch reactor. The HDS reactions proceeded through two parallel–consecutive reaction pathways: direct desulfurization (DDS) and hydrogenation (HYD), in which two main intermediates—biphenyl or 3,3′-dimethylbiphenyl and partially hydrogenated DBT or 4,6-DMDBT—were involved. Kinetic models were developed to account for the partial contributions of these intermediates in the overall reaction network as well as for their selectivities. The models allow a precise estimation of the apparent rate constants of all steps in the reaction network. In the HDS reactions of 4,6-DMDBT, the HYD pathway was more pronounced than the DDS route over the NMS catalyst. Different selectivities in terms of yield fraction (percentage ratio of HYD/DDS) were observed for these two catalysts. The kinetic results according to these models show that the partially hydrogenated 4,6-DMDBT intermediate transformed mainly to 3,3′-dimethylcyclohexylbenzene. Besides, this intermediate is suggested to be partly transformed to 3,3′-dimethylbiphenyl. The rate of sulfur removal from the partially hydrogenated 4,6-DMDBT intermediates was an order of magnitude slower than that from the partially hydrogenated DBT. The NiMo sulfide catalyst was more active than the CoMo sulfide catalyst for the HDS of 4,6-DMDBT. The results are discussed in the context of proposed HDS reaction networks.
Keywords: Hydrodesulfurization; Dibenzothiophene; 4,6-Dimehtyldibenzothiophene; Kinetic;

Detection of CO2 in solution with a Pt–NiO solid-state sensor by Zhao Yue; Wencheng Niu; Wei Zhang; Guohua Liu; Wolfgang J. Parak (227-231).
Response curves of ΔV RS from MISFET-based sensors with NiO–Pt thin film to different CO2 concentrations. (a) Variable voltage V DS, constant temperature T; (b) constant voltage V DS, variable temperature T.A metal insulator semiconductor field effect transistor (MISFET)-type sensor for the detection of CO2 dissolved in aqueous solution is presented. This all-solid-state device is based on a Pt–NiO thin film as active sensing material on the top of a gate electrode. The fabrication of the sensor is described and its performance is characterized. In particular the transient characteristics and response curves at different biases V RS versus the amount of dissolved CO2 are presented. The sensor shows a linear response to the logarithm of the concentration of dissolved CO2 at room temperature.
Keywords: MISFET; Pt–NiO thin films; Solution-based CO2 sensor;

An analytical solution for a partially wetting puddle and the location of the static contact angle by M. Elena Diaz; Javier Fuentes; Ramon L. Cerro; Michael D. Savage (232-239).
The figure on the left is a sketch, not at scale, of the profile of a sessile drop resting on a solid surface. The figure on the right is the exact solution for the angle of inclination of the drop as a function of the logarithm of drop height.A model is formulated for a static puddle on a horizontal substrate taking account of capillarity, gravity and disjoining pressure arising from molecular interactions. There are three regions of interest – the molecular, transition and capillary regions with characteristic film thickness, hm , ht and hc . An analytical solution is presented for the shape of the vapour–liquid interface outside the molecular region where interfacial tension can be assumed constant. This solution is used to shed new light on the static contact angle and, specifically, it is shown that.A second analytical solution for the shape of interface within the molecular region reveals that cos  θ has a logarithmic variation with film thickness, cos θ = cos θ o - ln [ 1 - h m 2 / 2 h 2 ] . The case, hm  = 0, is of special significance since it refers to a unique configuration in which the effect of molecular interactions vanishes, disjoining pressure is everywhere zero and the vapour–liquid interface is now described exactly by the Young–Laplace equation and includes a wedge of angle, θo , extending down to the solid substrate.
Keywords: Static contact angle; Transition region; Interface shape; Molecular forces; Wetting; 2D drop;

Elastocapillarity: Stress transfer through fibrous probes in wicking experiments by Daria Monaenkova; Konstantin G. Kornev (240-249).
In this paper, we analyze the mechanism by which a fibrous probe is stressed during the absorption of droplet.Current advances in the manufacture of nanoporous and nanofibrous materials with high absorption capacity open up new opportunities for the development of fiber-based probes and sensors. Pore structures of these materials can be designed to provide high suction pressure and fast wicking. During wicking, due to the strong capillary action, liquids exert stresses on the fiber network. In this paper, we discuss the effect of stress transfer in the direction of propagation of the wetting front. As an illustration, we first consider a single capillary and demonstrate the effect of a moving meniscus on stress distribution along capillary walls. We then analyze similar effects in yarns. We consider a yarn that can capture an aerosol droplet as a promising sensing element that could monitor the stresses caused by wetting fronts. We also discuss the elastocapillary effects occurring during upward and downward wicking. The distributions of stresses in these two cases are shown to differ significantly. We discuss how these effects might be exploited for designing fiber-based sensors that can probe very small amounts of liquids.
Keywords: Elastocapillarity; Wicking; Fibers; Deformations;

Spreading of completely wetting, non-Newtonian fluids with non-power-law rheology by Qi Min; Yuan-Yuan Duan; Xiao-Dong Wang; Zhan-Peng Liang; Duu-Jong Lee; Ay Su (250-254).
Spreading exponents of complete wetting, non-Newtonian fluids of non-power-law rheology with power-law model.Spreading non-Newtonian liquids with non-power-law rheology on completely wetting surfaces are seldom investigated. This study assessed the wetting behavior of polydimethylsiloxane (PDMS), a Newtonian fluid, two carboxymethylcellulose (CMC) sodium solutions, a PDMS + 2% w/w silica nanoparticle suspension and three polyethylene glycol (PEG400) + 5–10% w/w silica nanoparticle suspensions (non-power-law fluids) on a mica surface. The θ DU and Rt data for spreading drops of the six tested, non-power-law fluids can be described by power-law wetting models. We propose that this behavior is attributable to a uniform shear rate (a few tens to a few hundreds of s−1) distributed over the thin-film regime that controls spreading dynamics. Estimated film thickness was below the resolution of an optical microscope for direct observation. Approximating a general non-Newtonian fluid spreading as a power-law fluid greatly simplifies theoretical analysis and data interpretation.
Keywords: Spreading; Non-power-law; Power exponent; Spreading exponent; Contact angle;

Combination of forces required to disjoin the thin water film when probe (with/without oil) approaches the substrates.With an objective to understand the nature of forces which contribute to the disjoining pressure of a thin water film on a steel substrate being pressed by an oil droplet, two independent sets of experiments were done. (i) A spherical silica probe approaches the three substrates; mica, PTFE and steel, in a 10 mM electrolyte solution at two different pHs (3 and 10). (ii) The silica probe with and without a smeared oil film approaches the same three substrates in water (pH = 6). The surface potential of the oil film/water was measured using a dynamic light scattering experiment. Assuming the capacity of a substrate for ion exchange the total interaction force for each experiment was estimated to include the Derjaguin–Landau–Verwey–Overbeek (DLVO) force, hydration repulsion, hydrophobic attraction and oil-capillary attraction. The best fit of these estimates to the force–displacement characteristics obtained from the two sets of experiment gives the appropriate surface potentials of the substrates. The procedure allows an assessment of the relevance of a specific physical interaction to an experimental configuration. Two of the principal observations of this work are: (i) The presence of a surface at constant charge, as in the presence of an oil film on the probe, significantly enhances the counterion density over what is achieved when both the surfaces allow ion exchange. This raises the corresponding repulsion barrier greatly. (ii) When the substrate surface is wettable by oil, oil-capillary attraction contributes substantially to the total interaction. If it is not wettable the oil film is deformed and squeezed out.
Keywords: Thin water film; Disjoining pressure; Physical forces;

The superhydrophobic coatings are produced via deposition of a sodium stearate-stabilized dispersion of multiwalled carbon nanotubes utilizing superfluous acid.A waterproof biomaterial, stearic acid (STA), which is one of components of the wax present on the lotus leaf surface, was used as the material with low surface energy to fabricate superhydrophobic multiwalled carbon nanotube (MWCNT) hybrids through a solution method. This method involved preparation of a sodium stearate (SST)-stabilized MWCNT dispersion, followed by a precipitating process. STA was assembled on the MWCNT–SST hybrid surface by a reaction of SST with acetic acid. The rough surface with multiscale protuberances was revealed by scanning electron microscopy (SEM). The effect of SST/MWCNT weight ratio on water contact angle (CA) and the temperature dependence and alkali resistance of superhydrophobicity of MWCNT hybrids have been investigated. With increasing the SST/MWCNT weight ratio, the water CA of MWCNT hybrid increased and then decreased after a maximum value of 163° at the ratio of 1/1. It was interesting that the wetting property of MWCNT hybrids (SST/MWCNT = 0.5/1 and 1/1) was tunable between superhydrophobicity and superhydrophilicity by changing temperature. Potential applications of these superhydrophobic materials to make large-area superhydrophobic coatings have been proposed.
Keywords: Superhydrophobic hybrids; Carbon nanotubes; Stearic acid; Bionic fabrication;

Shear-induced suppression of rupture in two-layer thin liquid films by Sreeram K. Kalpathy; Lorraine F. Francis; Satish Kumar (271-279).
The effect of shear on the van-der-Waals-driven rupture of stratified thin liquid films confined between surfaces which may be chemically heterogeneous is examined.The effect of shear on the rupture of two stratified thin liquid films confined between parallel plates and subject to van der Waals forces is examined in this work. Lubrication theory is applied to derive a one-dimensional nonlinear evolution equation for the height of the liquid–liquid interface. Linear stability analysis reveals that the real part of the growth rate and the wavelength of the fastest growing interfacial disturbance are unaffected by shear. However, the growth rate has an imaginary part which is non-zero in the presence of shear, indicating the existence of traveling waves. Nonlinear simulations of interface behavior on homogeneous surfaces show that shear delays interfacial rupture, and suppression of rupture occurs beyond a critical shear rate. Propagation of traveling waves along the interface, and subsequent weakening of van-der-Waals-driven dewetting, is found to be the cause of the rupture delay. Analysis of flow on chemically heterogeneous surfaces also suggests a delay in interfacial rupture in the presence of shear. The problem studied here can serve as an idealized model for the lithographic printing process, and the results suggest that in the regime of shear rates relevant to printing, mechanisms of emulsification of one liquid into the other can be understood without incorporating shear. However, shear could be relevant in other physical systems such as nanofluidic and microfluidic flows.
Keywords: Thin liquid films; Shear; Rupture; Lithographic printing;

Controlling the stability and rheological properties of colloidal slurries has been an important but challenging issue for various industries such as cosmetics, ceramic processing, and nuclear waste treatment. For example, at the US Department of Energy Hanford and Savannah River sites, operation of the waste treatment facilities with increased solids loading increases waste processing rates but negatively impacts the rheological properties. We investigated various rheological modifiers on a Fe2O3/Al(OH)3-rich nuclear waste simulant, characterized by high ionic strength and pH, to reduce yield stress of the colloidal slurry. Rheological modifiers change particle interactions in colloidal slurries; they mainly alter the electrostatic and steric interactions, leading to a change in rheological properties. Weak acid-type rheological modifiers strengthen electrostatic repulsion whereas nonionic/polymer surfactant-type rheological modifiers introduce a steric repulsion. Using rheological analysis, it was found that citric acid and polyacrylic acid are good rheological modifiers for the simulant tested, effectively reducing yield stresses by as much as 70%. Further analysis supports the idea that adding these rheological modifiers increases the stability of the slurry. A likely mechanism for the observed effects of citric acid and polyacrylic acid on slurry behavior is identified as both binding cations in bulk solution and adsorption on the surface of the particles.Significant decreases in yield stress of the AZ-101 pretreated HLW simulant slurry due to citric and polyacrylic acids.
Keywords: Rheological modifiers; Colloidal interactions; Colloidal slurries; Yield stress; Nuclear waste simulant;

Oriented growth behavior of Ag nanoparticles using SDS as a shape director by Zhenquan Tan; Hiroya Abe; Makio Naito; Satoshi Ohara (289-292).
Control over the shape of Ag nanoparticles using SDS micelles as soft templates.We report a chemical approach for synthesizing shape-controlled Ag nanoparticles by using the surfactant SDS as a soft template. The experimental approach includes a two-step reaction: the first step is quickly generating Ag seed clusters by a chemical reaction using sodium borohydride as a reducing reagent; the second is the slow growth of controllable Ag nanoparticles by a mild chemical reaction using hydroxylamine hydrochloride as a reducing reagent. Spherical, polyhedral, and fibrous Ag nanoparticles are synthesized successfully in aqueous solution having SDS concentrations of 0.01, 0.02, and 0.2 wt.%, respectively. Size, morphology, and dispersion stability of these Ag nanoparticles depend on the concentrations of both SDS and AgNO3.
Keywords: Ag nanoparticles; SDS; Shape control; Soft template;

Reactive transport of arsenic(III) and arsenic(V) on natural hematite: Experimental and modeling by Javier Giménez; Joan de Pablo; Maria Martínez; Miquel Rovira; César Valderrama (293-297).
This figure represents experimental breakthrough curve of As((III) and As(V) onto natural hematite, as well as the calculations done with the theoretical model (two-site nonequilibrium sorption).Natural hematite was used for the removal of arsenic(III) and arsenic(V) from aqueous solution. The experimental breakthrough curves were obtained in fixed-bed columns. The transport of arsenic in a simplified fixed-bed configuration was quantified by using the CXTFIT code, which was used to estimate the transport and sorption parameters of the convective–dispersive equation (CDE) and the two-site deterministic nonequilibrium (TSM/CDE) model by fitting the models to the experimental breakthrough curves (BTC). The prediction of the breakthrough curves performed by the two-site nonequilibrium sorption model resulted in a good fit, indicating that this model can properly describe the transport and sorption processes of arsenic on natural hematite. Additionally the parameters obtained indicate that nonequilibrium sorption governs the As(III) and As(V) uptake onto hematite in a fixed-bed column. No significant differences in the transport and sorption parameters of As(III) and As(V) on natural hematite were obtained; the retardation factor values were in the same order of magnitude for both species.
Keywords: Arsenic(III); Arsenic(V); Natural hematite; Fixed-bed sorption; Two-site nonequilibrium model;