Journal of Colloid And Interface Science (v.364, #2)

Cover 1 (OFC).

The adsorption kinetics of cadmium by three different types of carbon nanotubes by Nancy V. Perez-Aguilar; Paola E. Diaz-Flores; Jose R. Rangel-Mendez (279-287).
Carbon nanotubes in solution may be suspended as single nanotubes or as agglomerates. Those possibilities were considered to predict cadmium adsorption kinetics with two diffusion models.Display Omitted► Three types of carbon nanotubes were used for cadmium adsorption at pH 6. ► Adsorption kinetics of each type of CNT was modeled by using two diffusion models. ► An intraparticle diffusion model best fitted the experimental kinetic data. ► The bamboo-type morphology of CNx favored the cadmium adsorption kinetics.Oxidized nitrogen-doped multiwall carbon nanotubes (ox-N-MWCNTs), oxidized multiwall carbon nanotubes (ox-MWCNTs), and oxidized single-wall carbon nanotubes (ox-SWCNTs) were evaluated via batch adsorption kinetic experiments to determine the effect of nanotube morphology on the adsorption rate of cadmium. The nanotubes were characterized by HRTEM, XRD and Raman spectroscopy. Cadmium adsorption isotherms were determined at pH 6. Analyses of the kinetic data with an external mass transport model and an intraparticle diffusion model considered two cases: (1) single nanotubes suspended in aqueous solution and (2) agglomerates of nanotubes suspended in aqueous solution. The intraparticle diffusion model produced the best fit to the experimental data. However, only the diffusivity coefficients for single nanotubes suspended in solution were similar to literature values: about 4 × 10−9, 1 × 10−9 and 2.4 × 10−11  cm2/s for ox-N-MWCNTs, ox-MWCNTs and ox-SWCNTs, respectively. The morphology of the various carbon nanotubes might determine cadmium diffusivity. The high amount of sidewall pores observed in the single-walled carbon nanotubes could limit cadmium diffusion and account for the slow diffusion rate of 180 min. Conversely, the short length, small surface area and bamboo-type morphology observed with nitrogen-doped multiwall carbon nanotubes may account for the relatively fast adsorption rate of 15 min as this morphology prevents cadmium diffusion through the internal tubular space of these nanotubes.
Keywords: Carbon nanotubes; Morphology; Toxic metals; Adsorption kinetics; Diffusion;

Efficient fabrication of ZrO2-doped TiO2 hollow nanospheres with enhanced photocatalytic activity of rhodamine B degradation by Chuanzhi Sun; Lichen Liu; Lei Qi; Hao Li; Hongliang Zhang; Changshun Li; Fei Gao; Lin Dong (288-297).
Ti1− x Zr x O2 hollow nanosphere exhibits higher photocatalytic activity than that of TiO2 hollow nanosphere, which is ascribed to increased specific surface areas and band gap.Display Omitted► ZrO2-doped TiO2 hollow nanospheres are efficiently fabricated without any surfactant or polyelectrolyte. ► The addition of Zr4+ obviously results in change in surface structures, phase structures, and pore size distribution. ► The incorporation of Zr4+ induces an enrichment of the electron charge density around Ti4+ ions. ► Ti1− x Zr x O2 hollow nanosphere-doped moderate ZrO2 exhibits the highest activity.ZrO2-doped TiO2 hollow nanospheres with anatase phase are efficiently fabricated via functionalized negatively charged polystyrene (PS) spheres without any surfactant or polyelectrolyte. The resulting Ti1− x Zr x O2 (hereafter denoted as TZ) hollow nanospheres are characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), powder X-ray diffraction (XRD), Laser Raman spectroscopy (LRS), X-ray photoelectron spectroscopy (XPS), X-ray fluorescence spectroscopy (XRF), nitrogen sorption, and UV–vis diffuse reflectance spectroscopy (UV–vis). The Zr4+ incorporation decreases the anatase crystallite size, increases the specific surface area, and changes the pore size distribution. Furthermore, it induces enrichment of electron charge density around Ti4+ ions and blueshift of absorption edges. The TZ hollow nanospheres doped with moderate ZrO2 (molar ratio, Ti:Zr = 10:1) exhibit better photocatalytic activity than the other samples for the degradation of rhodamine B in aqueous solution, which is correlated with the effect of Zr4+ doping on the physicochemical properties in terms of surface structures, phase structures, and the electronic structures.
Keywords: TiO2 hollow nanospheres; Ti1− x Zr x O2 hollow nanospheres; Photocatalytic activity; Rhodamine B;

Porous Fe3O4 nanoparticles: Synthesis and application in catalyzing epoxidation of styrene by Changliang Huang; Hongye Zhang; Zhenyu Sun; Yanfei Zhao; Sha Chen; Ranting Tao; Zhimin Liu (298-303).
The immobilization of Au onto the as-synthesized porous Fe3O4 particles with pore size around 2 nm significantly improved the catalytic performance of the catalyst for epoxidation of styrene to styrene oxide.Display Omitted► Porous Fe3O4 particles with pore size around 2 nm were synthesized via a simple route without structure-directing agent. ► The formation mechanism of the porous Fe3O4 particles was discussed. ► The obtained porous Fe3O4 particles were used to immobilize Au nanoparticles with the assistance of l-cysteine. ► The Au/l-Fe3O4 nanocomposite can effectively catalyze the epoxidation of styrene to styrene oxide with high performance.A facile route was employed to synthesize porous magnetite via reaction of FeCl3·6H2O with N2H4·H2O in ethylene glycol without any structure-directing agent. The resultant Fe3O4 particles were characterized by transmission electron microscopy, N2 adsorption, X-ray photoelectron spectroscopy, and thermal gravimetric analysis. It was demonstrated that the particle size varied in the range of 40–220 nm, and the pore size of particles was centered around 2 nm. The gases produced in the formation process of the particles played key role in the formation of the porous structure. The obtained porous magnetite was used as support to immobilize Au nanoparticles with size less than 2 nm with the assistance of l-cysteine. The as-prepared Fe3O4 particles can effectively catalyze epoxidation of styrene, and the immobilization of Au nanoparticles on the Fe3O4 support significantly improved the activity of the catalyst.
Keywords: Fe3O4; Porous nanoparticles; Epoxidation; Styrene;

Novel, highly selective gold nanoparticle patterning on surfaces using pure water by Muhammad Akram Raza; E. Stefan Kooij; Arend van Silfhout; Harold J.W. Zandvliet; Bene Poelsema (304-310).
Display Omitted► A simple novel method to locally adsorb gold nanoparticles is presented. ► Water treatment of mercaptosilane monolayers leads to ‘deactivation’ of thiol groups. ► A remarkably high degree of selectivity in deposited nanoparticles is demonstrated.We present a simple, novel procedure to selectively deposit gold nanoparticles using pure water. It enables patterning of nanoparticle monolayers with a remarkably high degree of selectivity on flat as well as microstructured oxide surfaces. We demonstrate that water molecules form a thin “capping” layer on exposed thiol molecules within the mercaptan self-assembled layer. This reversible capping of water molecules locally “deactivates” the thiol groups, therewith inhibiting the binding of metallic gold nanoparticles to these specific areas. This amazing role of water molecules can be used as a tool to pattern flat as well as structured surfaces with gold nanoparticles.
Keywords: Patterning; Gold nanoparticles; Selective deposition; Self-assembly; MPTMS;

Unified scaling behavior of physical properties of clays in alcohol solutions by Ravi Kumar Pujala; Nisha Pawar; H.B. Bohidar (311-316).
Display Omitted► Observation of universal scaling in clay dispersions in alcohol solutions. ► Correlation between size, zeta potential, viscosity and surface tension, and solvent polarity. ► Universality observed was independent of aspect ratio of the colloidal particles.This paper reports observation of universal scaling of physical properties of clay particles, Laponite (aspect ratio = 30) (L) and Na Montmorillonite (MMT, aspect ratio = 200), in aqueous alcohol solutions (methanol, ethanol and 1-propanol) with solvent polarity, defined through reaction field factor f OH(ɛ 0,  n) = [(ɛ 0  − 1/ɛ 0  + 2) − (n 2  − 1/n 2  + 2)], at room temperature (20 °C). Here, ɛ 0 and n are the static dielectric constant and refractive index of the solvent concerned. Physical properties (Z) such as zeta potential, effective aggregate size, viscosity and surface tension scaled with the relative solvent polarity as Z  ∼  δfα ; δf  = (f w(ɛ 0,  n) −  f OH(ɛ 0,  n)), where f w(ɛ 0,  n) is the reaction field factor for water, Z is the normalized physical property, and α is its characteristic scaling exponent. The value of this exponent was found to be invariant of aspect ratio of the clay but dependent on the solvent polarity only.
Keywords: Solvent polarity; Hydrophobicity; Unified scaling; Laponite; MMT;

TEM images of colloidal complexes of EGCG with MCE 4 formed at 1:1 w/w ratio (Scale bars 500 nm and 200 nm). The image clearly indicates appearance of spherical particles clustered together.Novelty of work: We demonstrate for the first time, simple fabrication of self associated colloidal complexes based on polymer–polyphenol interaction. Special consideration to their characterisation by ITC, in vitro release and antioxidant studies are also highlighted.Display Omitted► Epigallocatechin gallate:methylcellulose colloidal complex via simple addition. ► Binding parameters evaluated by Iso thermal titration calorimetry. ► Sustained release and improvement in antioxidant property of EGCG.The present work deals with the preparation and characterisation of colloidal complexes from association of water soluble cellulose derivative (methylcellulose) and green tea polyphenol–EGCG (Epigallocatechin gallate). Colloidal complexes with well defined size range of 95–300 nm (polydispersity index < 0.15) and a negative surface potential (−25 to −45 mV) were obtained by mixing solutions of methylcellulose and EGCG under vigorous stirring. The binding stoichiometry of 21 molecules of EGCG per one molecule of polymer was obtained from isothermal titration calorimetry. The free energy of binding (−31 kJ mol−1) is dominated by the binding enthalpy suggesting that the non-covalent complex is preferentially formed due to the hydrogen bonding. Transmission electron microscopy revealed almost spherical particle morphology of the formed colloidal complexes. Further, sustained release of EGCG from the complex in simulated in vitro media was observed which resulted in protecting the antioxidant property of EGCG in alkaline pH.
Keywords: Epigallocatechin gallate; Colloidal complex; Isothermal titration calorimetry; Methyl cellulose;

An eco-friendly route to magnetic silica microspheres and nanospheres by Sébastien Abramson; Wafa Safraou; Bernard Malezieux; Vincent Dupuis; Stephan Borensztajn; Emmanuel Briot; Agnès Bée (324-332).
The use of emulsions based on vegetable oils as alternative to existing methods for the preparation of iron oxide/silica particles leads to microsized or nanosized magnetic spheres depending on shearing rate.Display Omitted► A green alternative to obtain magnetic silica (MS) beads has been designed. ► Polydisperse microspheres or monodisperse nanospheres can be obtained. ► The nanocomposites compare well with MS beads synthesized by conventional methods. ► Hybrid MS microspheres modified by mercaptoporpyl moieties can also be prepared. ► Inorganic and hybrid MS microspheres were tested as adsorbents for heavy metals.A green and inexpensive alternative to existing methods for the preparation of magnetic iron oxide/silica nanocomposite particles has been investigated. The use of water-in oil emulsions based on vegetable oils instead of usual solvents led to microsized or nanosized magnetic silica spheres exhibiting similar characteristics to those of classical procedures. Furthermore this approach is very general since a large class of porous magnetic colloids differing in size or iron oxide fraction has been obtained. This work emphasizes the importance of the level of the shearing during the emulsification step with regard to the size and monodispersity of the prepared beads. All the materials prepared were fully characterized (SEM and TEM microscopies, SQUID magnetometry, N2 sorption volumetry, etc.). In addition, samples functionalized by thiol groups have been synthesized and successfully tested for the removal of heavy metals in water-treatment.
Keywords: Magnetic microspheres; Silica; Iron oxide; Nanocomposites; Green chemistry; Water-treatment;

Preparation of magnetically separable N-halamine nanocomposites for the improved antibacterial application by Alideertu Dong; Shi Lan; Jinfeng Huang; Tao Wang; Tianyi Zhao; Weiwei Wang; Linghan Xiao; Xin Zheng; Fengqi Liu; Ge Gao; Yuxin Chen (333-340).
Magnetic N-halamine nanocomposites with enhanced antibacterial activity against both Gram-positive and Gram-negative bacteria were synthesized and can be separated magnetically through the application of a magnetic field after antibacterial performance.Display Omitted► Successful encapsulation of magnetic silica nanoparticles with antibacterial polymeric N-halamines. ► Enhanced antibacterial activity of the magnetic N-halamine nanocomposites compared with their bulk counterparts. ► Perfect combination of magnetic and antibacterial property into one single entity.Magnetic N-halamine nanocomposites were synthesized through the encapsulation of the magnetic silica nanoparticles with antibacterial N-halamine polymer. The as-synthesized sample was characterized by transmission electron microscopy (TEM), dynamic light scattering (DLS), Fourier transform infrared (FTIR), X-ray diffraction (XRD), X-ray photoelectron spectra (XPS), and thermogravimetric analysis (TGA). The fabricated magnetic N-halamine nanocomposites possessed enhanced antibacterial activity against both Gram-positive and Gram-negative bacteria compared with their bulk counterparts. The effect of chlorine content of the magnetic N-halamine nanocomposites on the antibacterial activity was investigated. The magnetic N-halamine nanocomposites also exhibited super-paramagnetic behavior and had a saturation magnetization of 4.728 emu g−1 at room temperature, which made these nanocomposites separable magnetically after the antibacterial behavior. Performances derived from the synergism between magnetic core and antibacterial shell suggest that the magnetic N-halamine nanocomposites are qualified for antibacterial applications and separable by the aid of the external magnetic field.
Keywords: Magnetic; N-halamine; Nanocomposites; Antibacterial; Separation;

Aqueous dispersions of colloidal poly(3-hexylthiophene) gel particles with high internal porosity by Jeffrey J. Richards; Kathleen M. Weigandt; Danilo C. Pozzo (341-350).
Poly(3-hexylthiophene) gel particles offer a flexible route to forming porous thin films. This promises a simpler approach to producing bulk heterojunction structures in organic solar cells.Display Omitted► Gel particle dispersions made from P3HT organogels for organic solar cells. ► Size and porosity of particles were dependent on bulk organogel concentration. ► Dispersions found to retain the electronic and optical signatures of parent organogels. ► Organic solar cells produced by spray-coating dispersions with soluble fullerene.This work outlines the development of nano-porous, sub-micron poly(3-hexylthiophene) (P3HT) gel particles as solution-processable inks for applications in polymer solar cells. These dispersions are produced by emulsifying bulk P3HT organogels into water containing surfactant. The optical characteristics and stability of the resulting gel particles are assessed and their structure characterized. The P3HT within the gel particles is shown to retain its crystallinity with no evidence of doping. The gel particles are shown to be stable against aggregation due to the presence of surfactant at the oil/water interface. The fracture of the gel network during emulsification produces a bimodal distribution of particles that increase in size with increasing P3HT concentration in the ‘parent’ organogel. Small Angle Neutron Scattering measurements show that the particles maintain the structure of the bulk gels with high specific surface area. Spray-coating the gel particle dispersions produces uniform thin-films, which have been used to fabricate polymer/fullerene solar cells with a fully spray-coated active layer.
Keywords: Poly(3-hexlythiophene); Gel particle; Dispersions; Solar cell; Organogel;

Surface and friction forces between grafted polysaccharide layers in the absence and presence of surfactant by Cathy E. McNamee; Shinpei Yamamoto; Michael Kappl; Hans-Jürgen Butt; Ko Higashitani; Andra Dėdinaitė; Per M. Claesson (351-358).
The effect of a grafted polysaccharide layer and the presence of a surfactant on the surface and friction forces between two silica surfaces was investigated by the AFM using two bare silica surfaces, a bare- and a polysaccharide grafted silica surface, and two polysaccharide grafted silica surfaces in the absence and presence of sodium dodecyl sulfate.Display Omitted► We study interactions between chemically grafted polysaccharide layers in water. ► We synthesize and graft an end-terminated dextran silane coupling agent to silica. ► A bridging attraction was seen between a silica surface and a polydextran surface. ► Repulsive forces and high friction were seen between two polydextran surfaces. ► Addition of surfactant enhanced the repulsive forces and decreased the friction.We analyzed the interaction between chemically grafted polysaccharide layers in aqueous solutions. To fabricate such layers, an end-terminated dextran silane coupling agent was synthesized and the polydextran was grafted to oxidized silicon wafers and to silica particles. This resulted in the formation of a 28 nm thick layer (in air) and a grafted amount of 40 mg/m2 as determined by ellipsometry. The physical properties of the grafted layer were investigated in aqueous solutions by atomic force microscope imaging and colloidal probe force measurements. Surface and friction forces were measured between one bare and one polydextran coated silica surface. A notable feature was a bridging attraction due to affinity between dextran and the silica surface. Surface interactions and friction forces were also investigated between two surfaces coated with grafted polydextran. Repulsive forces were predominant, but nevertheless a high friction force was observed. The repulsive forces were enhanced by addition of sodium dodecyl sulfate (SDS) that associates with the tethered polydextran layers. SDS also decreased the friction force. Our data suggests that energy dissipation due to shear-induced structural changes within the grafted layer is of prime importance for the high friction forces observed, in particular deformation of protrusions in the surface layer.
Keywords: Dextran; Silane coupling agent; Polymer layer; Silica; Friction; Surface forces; Adhesion; Tethered polysaccharide; AFM; Ellipsometry;

The reduction of Ag+ in metallic silver on pseudomelanin films allows for antibacterial activity but does not imply unpaired electrons by Vincent Ball; Isabelle Nguyen; Michael Haupt; Christian Oehr; Claire Arnoult; Valérie Toniazzo; David Ruch (359-365).
Display Omitted► Deposition of melanin films. ► Mechanism of silver deposition. ► Electron spin resonance and XPS spectroscopy. ► Antibacterial activity.Dopamine–melanin films produced through the oxidation of dopamine in the presence of oxygen as an oxidant allow to reduce silver ions onto silver particles as already described in the paper by Lee et al. (H. Lee, S.M. Dellatore, W.M. Miller, P.B. Messersmith, Science 318 (2007) 426.). This reduction process has to occur through the oxidation of moieties present in the melanin film. This investigation shows that the free radicals present in the pseudomelanin film, quantified by means of electron spin resonance spectroscopy (ESR) for the first time, are not used in the transformation of Ag+ cations to deposit silver. The ESR signal is hardly affected by the deposition of silver particles. On the other hand, X-ray photoelectron spectroscopy shows a small increase in the density of quinone groups and a small decrease of catechol groups on the surface of the film during the deposition of silver. This suggests that the deposited pseudomelanin films contain a significant fraction of catechol groups able to trigger reduction processes of metallic cations. These silver nanoparticles remain adherent to the melanin films and allow for a quantitative killing of Escherichia coli over a broad range of bacterial dilutions. However, the presence of the bacteria induces a release of the nanoparticles. The pseudomelanin films cannot be reused again for a silver ion reduction step. Nevertheless, the easy preparation of the pseudomelanin–silver composite and its effective one shot bacterial killing activity renders the strategy presented in this paper attractive. Some fundamental questions about redox process allowed by the pseudomelanin films will also be asked.
Keywords: Pseudomelanin films; Electron spin resonance spectroscopy; X-ray photoelectron spectroscopy; Silver; Antibacterial activity;

Solvent colorimetric paper-based polydiacetylene sensors from diacetylene lipids by Suricha Pumtang; Warathip Siripornnoppakhun; Mongkol Sukwattanasinitt; Anawat Ajavakom (366-372).
Display Omitted► The solvent paper-based sensors were prepared from novel diacetylene monomers. ► The colorimetric respond to solvents changed from blue to red pattern was recorded as RGB values. ► Principal component analysis (PCA) of RGB gave good solvent discriminating results. ► According to the PCA score plot, this paper-based sensors can identify 11 organic solvents.A well known unique property of polydiacetylenes (PDAs) is the colorimetric response to external stimuli making it one of the most studied conjugated polymers for sensing applications. Here we report the synthesis of a novel series of diacetylene acids from the condensation of pentacosa-10,12-diynylamine (PCDAmine) and dicarboxylic acid or its anhydrides. One of these diacetylene lipids, 4-(pentacosa-10,12-diynylamino)-4-oxobutanoic acid (PCDAS), is used in combination with pentacosa-10,12-diynoic acid (PCDA) for dropcasting on pieces of filter paper which are consequently irradiated by UV light to generate a paper based sensor array for solvent detection and identification. Upon the exposure to various types of organic solvents, the blue colored sensors colorimetrically respond to give different shades of colors between blue to red. The color patterns of the sensor array are recorded as RedGreenBlue (RGB) values and statistically analyzed by principal component analysis (PCA). The PCA score plot reveals that the array is capable of identifying eleven common organic solvents.
Keywords: Chromism; Polydiacetylene; Sensor array; Statistical analysis; VOC;

In situ preparation of Al-containing PVDF ultrafiltration membrane via sol–gel process by Ruizhi Pang; Jiansheng Li; Kajia Wei; Xiuyun Sun; Jinyou Shen; Weiqing Han; Lianjun Wang (373-378).
A new method for the preparation of Al-containing PVDF ultrafiltration membrane was reported. The method combines sol–gel process with traditional immersion precipitation process. Well-dispersed inorganic nanoparticles with the size of 10–20 nm were obtained in PVDF matrix.Display Omitted► A simple in situ method for the preparation of Al-containing PVDF membrane was developed. ► The strategy is to combine sol–gel process with immersion precipitation process. ► This method could provide a good dispersion of Al species in PVDF matrix. ► The hydrophilic property of membrane was enhanced greatly.Recently, inorganic nanoparticles blended within polymeric membranes have shown improved antifouling performance in wastewater treatment. However, agglomeration of nanoparticles remains as one of the major obstacles for generating a uniform surface. In this study, a new method for in situ preparation of Al-containing PVDF ultrafiltration membranes to improve the dispersion of nanoparticles is reported. The strategy of this method is to combine sol–gel process with traditional immersion precipitation process. Al sol was synthesized by the addition of anionic exchange resin in N,N-dimethylformamide (DMF) solvent containing aluminum chloride. Homogeneous Al-containing PVDF casting solution was then obtained by dissolving PVDF polymer in the Al sol. The membrane formation mechanism was investigated by precipitation kinetics and morphology. Results indicate that the addition of Al species can accelerate phase inversion of casting solution. Scanning electron microscopic images show that a typical transition from sponge-like structure to finger-like structure occurred with increasing Al species content. The existence and dispersion states of Al species in the resultant membrane matrix were further examined by transmission electron microscope and X-ray photoelectron spectrometer. The results indicate the Al species nanoparticles were well dispersed throughout PVDF matrix. Dynamic BSA fouling resistance experiments demonstrate the Al-containing PVDF membranes possess improved separation performances over the pure PVDF membranes.
Keywords: PVDF membrane; Sol–gel process; In situ preparation; Al sol;

The role of glycerol and phosphatidylcholine in solubilizing and enhancing insulin stability in reverse hexagonal mesophases by Idit Amar-Yuli; Doron Azulay; Tehila Mishraki; Abraham Aserin; Nissim Garti (379-387).
Insulin solubilization has been studied in several mesophases demonstrating the potential of liquid crystalline mesophases (based on GMO) and glycerol as a cosolvent for protein entrapment and protection.Display Omitted► Insulin was solubilized and thermally stabilized in advanced soft-matter structures. ► Insulin confinement within HII cylinders is more restricted compared to that in water. ► Insulin thermal stability was significantly enhanced. ► The formation of disease-related fibrils was hampered.The potential of reverse hexagonal mesophases based on monoolein (GMO) and glycerol (as cosolvent) to facilitate the solubilization of proteins, such as insulin was explored. HII mesophases composed of GMO/decane/water were compared to GMO/decane/glycerol/water and GMO/phosphatidylcholine (PC)/decane/glycerol/water systems. The stability of insulin was tested, applying external physical modifications such as low pH and heat treatment (up to 70 °C), in which insulin is known to form ordered amyloid-like aggregates (that are associated with several neurodegenerative diseases) with a characteristic cross β-pleated sheet structure.The impact of insulin confinement within these carriers on its stability, unfolding, and aggregation pathways was studied by combining SAXS, FTIR, and AFM techniques. These techniques provided a better insight into the molecular level of the “component interplay” in solubilizing and stabilizing insulin and its conformational modifications that dictate its final aggregate morphology.PC enlarged the water channels while glycerol shrank them, yet both facilitated insulin solubilization within the channels.The presence of glycerol within the mesophase water channels led to the formation of stronger hydrogen bonds with the hosting medium that enhanced the thermal stability of the protein and remarkably affected the unfolding process even after heat treatment (at 70 °C for 60 min).
Keywords: Liquid crystals; Proteins; FTIR; AFM; SAXS; Monoolein;

Aggregation behavior of a model ionic liquid surfactant in monosaccharide + water solutions by Yujuan Chen; Yang Zhao; Jing Chen; Kelei Zhuo; Jianji Wang (388-394).
Concentration dependence of the conductivities for [C10mim]Cl in water and in glucose + water solutions.Display Omitted► Monosaccharides enhance the aggregation of the ionic liquid [C10mim]Cl in solution. ► Stereo-structures of monosaccharides influence aggregation of [C10mim]Cl. ► Sizes of the aggregates increase slightly with molalities of monosaccharides.Alkylimidazolium salts are a very important class of ionic liquids (ILs). The ILs containing long alkyl chains are a kind of model surfactants. In this paper, the aggregation behavior of 1-decyl-3-methylimidazolium chloride ([C10mim]Cl) was investigated for the first time in aqueous monosaccharide (glucose, galactose, xylose and arabinose) solutions by conductivity, fluorescence, NMR and dynamic light scattering (DLS). Thus a series of physico-chemical parameters for the aggregation of [C10mim]Cl—the critical aggregation concentration (CAC), ionization degree of the aggregates (α), the standard Gibbs energy of aggregation ( Δ G m 0 ), and the aggregation number (N) were derived from the experimental data. The results show that addition of small amounts of monosaccharides in aqueous solution can cause a variation in aggregation properties of the IL. The CAC values decrease with increasing molality of monosaccharides. In particular for different kinds of monosaccharides, we found that the CAC values are in the order: glucose > galactose (hexoses), xylose > arabinose (pentoses); xylose > glucose (1e2e3e4e), arabinose > galactoses (1e2e3e4a). These trends may be attributed to the slight difference in the stereo-structure of monosaccharide molecules. Finally a mechanism for the interaction of these monosaccharides with [C10mim]Cl was proposed.
Keywords: Aggregation; Fluorescence; Ionic liquids; Monosaccharides; NMR spectroscopy;

Interaction of a new surface sensitive probe compound with anionic surfactants of varying hydrophobic chain length by Arnab Maity; Prasun Ghosh; Tarasankar Das; Jyotirmayee Dash; Pradipta Purkayastha (395-399).
Small aggregates of surfactant monomers start to form after addition of surfactant and coalesce at different critical aggregation constants until they reach the critical micellar concentration. Different sizes of the aggregates are believed to affect the binding of the probe molecules to the surface.Display Omitted► The added probe binds to the surface of the surfactant micelles. ► The equilibrium shifts between neutral and ionic forms of the probe on binding. ► Surfactant monomers are suggested to form small aggregates that coalesce to become bigger.The amide derivative of a bis-phenylethynyl compound meta linked to 2,6-pyridine (BPEAP) poses inherent equilibrium between its neutral and zwitterionic forms in the excited state. BPEAP has been found to bind to the surface of anionic micelles instead of penetrating inside. This phenomenon has been exploited to attempt controlling the process of equilibrium using sodium dodecyl sulfate (SDS) at its pre-micellar and near-micellar aggregation concentrations. The anionic surfactant has been found to alter the equilibrium between the said forms of BPEAP depending on its concentration in solution. The process has been further verified by using sodium decyl sulfate (SDeS), which has smaller hydrophobic chain length than SDS as also varies in the critical micellar concentration (CMC) and aggregation number. The binding constant of the probe to the surfactant aggregates varies depending on the extent of surface available to the fluorophore for attachment.
Keywords: Surface binding probe; Neutral-ionic equilibrium; Surfactant aggregate; Different hydrophobic chain length; Binding constant;

The figure and the inset represent the change of fluorescence peak intensity with increasing [TX-100] in water and cyclohexane, respectively measured by non-invasive method. The CMC of TX-100 can be estimated from the break point of the graphs.Display Omitted► CMC of TX-100 determined by non-invasive methodology. ► Micellar and Reverse Micellar systems characterized. ► Structural perturbations induced by external fluorophores avoided. ► Steady-state and time-resolved measurements are highly correlated. ► Three external probes used also support the non-invasive technique.In this present study, we report on new methodology for determining the Critical Micelle Concentration (CMC) of a neutral surfactant Triton X-100 (TX-100) both in aqueous and non-aqueous media based on a non-invasive approach. The presence of the phenyl moiety of TX-100 was made use of as an intrinsic fluorophore and steady-state and time-resolved spectroscopy has been used to characterize the micellar systems. There are reports that external fluorophores may bring about some structural changes in the systems and the perturbations caused by these fluorophores in micellar systems may affect the shape and size of the micelles. We have also used three probes namely ANS, Rh6G and C-480 to determine the CMC of TX-100 both in aqueous and non-aqueous media and the values obtained agree very well with those estimated by the non-invasive techniques. Interestingly, for our system, we have conclusively proved that the external probes have almost no effect on the process of micellization. Although, both the invasive and non-invasive technologies report almost the same values of CMC, yet the latter methodology is free from any external perturbations and this makes the micellar/reverse micellar system, which may interact with other biological systems less prone to any physical distortions.
Keywords: Steady-state and time-resolved spectroscopy; Critical Micelle Concentration; Non-invasive techniques;

Thermal-stability of mixed giant micelles of alkyltrimethylammonium surfactants and salicylate by Roberta K. Rodrigues; Thiago H. Ito; Edvaldo Sabadini (407-412).
A giant micelle changes its conformation within the flow and breaks above certain critical temperature.Display Omitted► Giant micelles promote hydrodynamic drag reduction (HDR). ► Thermal synergism in mixed giant micelle was investigate using such property. ► The HDR is lost if the micelles is thermally broken. ► Synergism increases if a shorter surfactant is combined with a longer. ► This is due to the better packing of the molecules that form the mixed micelles.When diluted solutions of giant micelles are under turbulent flow, large attenuations of the turbulence can be observed due to the action of the micelles on the dissipative vortices formed within the flow. This particular property is rapidly lost when the solution is heated due breakup of the giant micelles. Based on this property, we present a thermal-flow study of a mixed giant micelle formed by the combination of two surfactants and sodium salicylate. One of the surfactants, cetyltrimethylammonium bromide (C16TAB) was kept fixed, and the others were dodecyltrimethylammonium bromide (C12TAB), tetradecyltrimethylammonium bromide (C14TAB), octadecyltrimethylammonium bromide (C18TAB), polyoxyethylene (10) oleyl ether (Brij 97) or sodium dodecyl sulfate (SDS). Thermal diagrams for the combinations of the surfactants reveal deviations of the ideality. For the cationic surfactants, a synergistic effect was only observed when C16TAB was combined with the shorter surfactants.
Keywords: Giant mixed micelles; Thermal stability; Synergism; Flow properties;

A Gibbs-Duhem type relation is presented for a two-component mixed micelle consisting of an ionic(red) and a nonionic(white) surfactant species.Display Omitted► A derivation of the micellar Gibbs–Duhem relation for ionic/nonionic mixed micelles is presented. ► The result at constant temperature and pressure is similar as that proposed by D.G. Hall. ► The present approach without recourse to the Donnan equilibrium is simpler than that of Hall.The micellar Gibbs–Duhem relation for two-component ionic/nonionic mixed micelles is presented in terms of the apparent bound amount to micelles. For simplicity, the ionic surfactant and a salt are both uni-uni valent electrolytes and have a common counterion species. Compared to the theory by D.G. Hall on the basis of a consideration on the Donnan equilibrium [D.G. Hall, J. Chem. Soc. Faraday Trans. 87 (1991) 3529], the present approach is simple and unambiguous. Considering changes at constant temperature and pressure, the two approaches provide nearly identical results.
Keywords: Mixed micelles; The Gibbs–Duhem relation; The dressed micelle model; Ionic surfactant; Counterion binding;

SDS surfactant is adsorbed by either its hydrophilic or hydrophobic part on the different cell orientationsDisplay Omitted► Properties of SDS surfactant at rutile/water interfaces are investigated. ► Rutile cell orientations (1 0 0), (0 0 1) and (1 1 0) are studied. ► Different SDS structures are formed at the different cell orientations. ► Behavior of surfactant molecules on the (1 0 0) surface is similar to that in graphite.Molecular dynamics simulations to study the behavior of an anionic surfactant close to TiO2 surfaces were carried out where each surface was modeled using three different crystallographic orientations of TiO2 (rutile), (0 0 1), (1 0 0) and (1 1 0). Even though all three surfaces were made with the same atoms the orientation was a key to determine adsorption since surfactant molecules aggregated in different ways. For instance, simulations on the surface (1 0 0) showed that the surfactant molecules formed a hemicylinder structure whereas the molecules on the surface (1 1 0) were attached to the solid by forming a hemisphere-like structure. Structure of the aggregated molecules and surfactant adsorption on the surfaces were studied in terms of tails and headgroups density profiles as well as surface coverage. From density profiles and angular distributions of the hydrocarbon chains it was possible to determine the influence of the solid surface. For instance, on surfaces (1 0 0) and (0 0 1) the surfactant molecules formed molecular layers parallel to the surface. Finally, it was found that in the solids (1 0 0) and (1 1 0) where there are oxygen atoms exposed on the surface the surfactant molecules were attached to the surfaces along the sites between the lines of these oxygen atoms.
Keywords: Computer simulations; SDS surfactant; Adsorption; Rutile;

Polydiacetylene-supported silica films formed at the air/water interface by Yelena Demikhovsky; Sofiya Kolusheva; Margarita Geyzer; Raz Jelinek (428-434).
Thin films of polydiacetylene and silica were produced at the air/water interface. Polydiacetylene acts both as a scaffolding for the free-standing silica matrix, as well as a colorimetric and fluorescent reporter of soluble analytes. The polydiacetylene/silica films were used for chromatic sensing of bacteria.Display Omitted► Thin films of silica and polydiacetylene were assembled at the air/water interface. ► Polydiacetylene facilitated formation of the “free-standing” silica film. ► The two components are essential for film stability and homogeneity. ► The unique colorimetric properties of PDA were retained in the mixed films. ► The silica/PDA films were employed for bacterial detection.Mesostructured silica films have attracted interest as potential platforms for sensing, molecular sieving, catalysis, and others. The fabrication of free-standing silica films on water, however, is challenging due to the need for scaffolding agents that would constitute effective templates. We describe the assembly of thin film at the air/water interface comprising quaternary silicates and polydiacetylene (PDA), a unique chromatic polymer forming two-dimensional conjugated networks, and the use of these films for biological sensing. PDA exhibits a dual role in the system—both as the amphiphilic matrix facilitating immobilization of the silicate colloidal units at the air/water interface and additionally a chromatic reporter that undergoes visible blue–red transitions, accompanied by fluorescence transformations, in the presence of analytes. We demonstrate the application of the silicate/PDA thin films for the detection of bacterial proliferation.
Keywords: Polydiacetylene; Mesostructured silica films; Color sensors; Free-standing thin films; Langmuir monolayers; Bacterial sensors;

Surface structure and catalytic properties of MoO3/CeO2 and CuO/MoO3/CeO2 by Wujiang Yu; Jie Zhu; Lei Qi; Chuanzhi Sun; Fei Gao; Lin Dong; Yi Chen (435-442).
The results showed that the molybdena modification with high Mo loading promoted the dispersion of CuO due to the formation of new tetrahedral vacancies.Display Omitted► Molybdena monolayer–modified CeO2 increases the dispersion capacity of copper oxide. ► MoO3/CeO2 samples with different MoO3 loadings have different structures. ► After the addition of CuO, the structures of molybdena species change significantly. ► The surface acidity is related to the molybdena species structures tightly. ► The active sites of CuO/MoO3/CeO2 in ‘‘NO + NH3  + O2’’ reaction are proposed.XRD, LRS, TPR and in situ NH3 adsorption FT-IR were used to investigate the dispersion state of the copper oxide and molybdena species of MoO3/CeO2 and CuO/MoO3/CeO2 catalysts as well as their surface acidity. The results showed that the molybdena monolayer modification promoted the dispersion of CuO due to the formation of new tetrahedral vacancies. Meanwhile, CuO changed the structure of molybdenum species and then influenced the surface acidity of the samples. A detail discussion about the possible model of the surface structure of the catalyst was presented. In addition, combining with the in situ NH3 adsorption FT-IR, the relationships between the activities for ‘‘NO + NH3  + O2’’ reaction and surface acid properties (Brønsted and Lewis acid sites) of the catalysts were discussed.
Keywords: CuO/MoO3/CeO2; Surface structure; Surface acidity; NO + NH3  + O2;

Influence of montmorillonite tactoid size on Na–Ca cation exchange reactions by Christophe Tournassat; Mohamed Bizi; Gilles Braibant; Catherine Crouzet (443-454).
Clay tactoid size and organisation (left figure) as a function of experimental conditions for Na-Ca exchange on montmorillonite (right figure) can explain the measured changes in selectivity coefficient values (middle figure).Display Omitted► The clay platelet stacking arrangement influences the relative affinities for cations. ► We quantified the link between exchange properties and tactoid size and organisation. ► We coupled the tactoid size to Na/Ca affinities of external and interlayer surfaces.The spatial organisation of swelling clay platelets in a suspension depends on the chemical composition of the equilibration solution. Individual clay platelets can be well dispersed, with surfaces entirely in contact with the external solution, or be stacked in tactoids, where part of the surfaces forms parallel alignments embedding interlayer water and cations. External and interlayer surfaces do not exhibit similar affinities for cations having different hydration and charge properties and the clay platelet stacking arrangement influences the clay affinity for these cations. This paper aims to establish the link between exchange properties and clay tactoid size and organisation for Na–Ca exchange on montmorillonite. Different montmorillonite samples behave differently with regards to Na–Ca exchange, from ideal to non-ideal exchange behaviour. A simple model coupling the tactoid stacking size to different Na/Ca relative affinities of the external and interlayer clay surfaces enables these differences to be reproduced.
Keywords: Cation exchange; Montmorillonite; Tactoid; Stacking; Compaction; Model;

Phosphate uptake by TiO2: Batch studies and NMR spectroscopic evidence for multisite adsorption by Sue A Kang; Wei Li; Hyo Eun Lee; Brian L. Phillips; Young Jae Lee (455-461).
Four major resonances for six samples prepared under different conditions of pH and phosphate loading show the existence of multiple types of phosphate adsorption complexes.Display Omitted► Phosphate sorption on TiO2 was examined by batch experiments and NMR spectroscopy. ► The sorption of phosphate on TiO2 decreases with increasing pH. ► The phosphate sorption is rapid and mostly irreversible at pH 4.5 and 7.0. ► NMR indicates that the phosphate sorbed on TiO2 forms inner-sphere surface complexes.Systematic studies, combining batch experiments with NMR spectroscopic methods, are carried out for phosphate sorption on titanium dioxide (TiO2). It is found that phosphate sorption on TiO2 decreases with increasing pH, whereas the phosphate uptake by TiO2 increases with increasing ionic strength of the solution. In I  ⩽ 0.1 M, the sorption sharply increases and reaches a near maximum and then followed by little changes showing Langmuir-type behavior, whereas in I  = 0.7 M, non-Langmuirian uptake becomes evident as equilibrium phosphate concentrations increase in solution. The sorption of phosphate on TiO2 is rapid and mostly irreversible at pH 4.5 and 7.0. At pH 9.0, however, the phosphate sorption is initially reversible and followed by resorption of phosphate on TiO2 at the system re-equilibration. 31P{1H} cross-polarization and magic angle spinning (CP/MAS) NMR spectra contain at least four main peaks which appear similar in position and width under all adsorption conditions, but vary in intensity with surface loading. The spectral characteristics of these peaks, including cross-polarization dynamics and chemical shift anisotropy obtained from spinning sideband analysis, suggest that they arise from distinct inner-sphere adsorption complexes, most of which are protonated. These results indicate that uptake of phosphate by TiO2 occurs by formation of several types of surface complexes.
Keywords: Phosphate; Titanium dioxide (TiO2); Sorption isotherm; Nuclear magnetic resonance (NMR); Cross-polarization and magic angle spinning (CP/MAS); Inner-sphere adsorption surface complexes;

Phenol can be effectively removed by MCl at both acidic and alkaline pH. The maximum adsorption capacities of phenol on MCl at pH 6.6 and 11.2 were 80.2 and 92.9 mg/g, respectively.Display Omitted► Phenol can be effectively removed by MCl at both acidic and alkaline pH. ► The maximum adsorption was achieved at about pH 11. ► Desorption of phenol can be easily achieved. ► MCl can simultaneously remove phenol and Cr(VI) from their mixtures. N-butylimidazolium functionalized strongly basic anion exchange resin with Cl anion (MCl) was prepared by anchoring N-butylimidazole onto chloromethylated macroporous styrene–divinylbenzene (St-DVB) copolymer. The adsorption performances of phenol on MCl were studied using the batch technique at acidic and alkaline pH. The studies showed that phenol can be effectively removed at both acidic and alkaline pH. The maximum adsorption was achieved at about pH 11. The maximum adsorption capacities of phenol on MCl at pH 6.6 and 11.2 were 80.2 and 92.9 mg/g, respectively. The adsorption mechanism was mainly molecular adsorption at acidic pH and anion exchange at alkaline pH. The adsorption of phenol was hindered by the presence of Cl and SO 4 2 - at alkaline pH due to the competitive anion exchange reaction. The adsorption of molecular phenol species on MCl at acidic pH was exothermic, and the anion exchange of phenolate species by MCl at alkaline pH was endothermic. Desorption of phenol from loaded adsorbent was achieved by using 0.5 mol/L NaOH and 0.5 mol/L NaCl mixed solution. MCl can simultaneously remove phenol and Cr(VI) from their mixtures, which would be of practical value in actual industrial wastewater treatment.
Keywords: Phenol; Adsorption; Anion exchange resin; Supported ionic liquids;

Interaction of phenol and dopamine with commercial MWCNTs by Ajna Tóth; Andrea Törőcsik; Etelka Tombácz; Erzsébet Oláh; Marc Heggen; Chengliang Li; Erwin Klumpp; Erik Geissler; Krisztina László (469-475).
The occupied area on pristine CNT is independent of ΔG, pH and probe molecule (filled symbols). The pronounced trend on oxidized CNT (open symbols) points to a different sorption mechanism.Display Omitted► Adsorption of phenol and dopamine is compared on commercial MWCNTs. ► Adsorption data of dopamine are reported first time. ► Different pH dependence of adsorption on non-treated and oxidized CNTs. ► The surface coverage is 8–12% and 21–33% with phenol and dopamine, respectively. ► Interaction is stronger but capacity is much smaller than with activated carbons.We report the adsorption of phenol and dopamine probe molecules, from aqueous solution with NaCl, on commercial multiwall carbon nanotubes (MWCNT) and on their carboxylated derivative. The nanotubes were fully characterized by high resolution transmission electron microscopy (HRTEM), small angle X-ray scattering (SAXS), potentiometric titration, electrophoretic mobility, and nitrogen adsorption (77 K) measurements. The experimental pollutant isotherms, evaluated using the Langmuir model, showed that only 8–12% and 21–32% of the BET surface area was available for phenol and dopamine, respectively, which is far below the performance of activated carbons. Influence of the pH was more pronounced for the oxidized MWCNT, particularly with dopamine. The strongest interaction and the highest adsorption capacity occurred at pH 3 with both model pollutants on both types of nanotubes. Although the surface area available for adsorption is far lower in MWCNTs than in activated carbons, it is nonetheless substantial. In particular, delayed release of toxic molecules that are either adsorbed on the surface or trapped in the inner bore of such systems could constitute an environmental hazard. The need for further adsorption studies with regard to their environmental aspects is therefore pressing, particularly for MWCNTs in their functionalized state.
Keywords: Multiwall carbon nanotube; Adsorption; pH; Aqueous phase; SAXS;

The DFT-based reaction pathway calculation indicated that the bidentate binuclear (BB) adsorption structure of arsenate on TiO2 surfaces evolved from a monodentate mononuclear (MM) metastable-equilibrium adsorption (MEA) state.Display Omitted► Transition states and intermediate species of arsenate adsorption on TiO2 surfaces. ► The interrelation between different adsorption complexes was revealed. ► The BB adsorption state evolved from a MM metastable-equilibrium adsorption state. ► This two-step adsorption process provided an interpretation of the C 0 effect.Reaction pathway information of transition states and intermediate species is crucial for understanding the adsorption mechanism of pollutants at mineral–water interfaces. However, it has been difficult to obtain such information using existing experiments. Here, the activation barriers, transition states, intermediate species and surface complexes of arsenate adsorption on TiO2 surfaces were studied using DFT-based reaction pathway calculations. The results indicated that the bidentate binuclear (BB) adsorption structure was formed through a monodentate mononuclear (MM) metastable-equilibrium adsorption (MEA) state. A two-step adsorption mechanism was proposed on the basis of the detailed picture of bond breaking and bond formation during each reaction step. When the adjacent surface sites were occupied, the transform from MM mode to BB mode was greatly inhibited so that both MM and BB coexisted in the equilibrium adsorption sample. The BB complex was energetically more stable than the MM complex, and so, the adsorption irreversibility was fundamentally related to the ratio BB:MM in the final equilibrium state. This mechanism may also explain the initial concentration effect, where, for the given adsorption experiment of arsenate on TiO2 under the same thermodynamic conditions, both equilibrium constants and the BB:MM ratio in equilibrium adsorption samples changed with the reaction kinetics.
Keywords: Transition state; Activation barrier; MEA state; Surface reactivity; Adsorption reaction pathway; Surface coverage;

Pt ions was selectively absorbed on the resin by stronger bonding forces..Display Omitted► Only Si, Pt, Rh and Pd from the solution were selectively adsorbed on the resin Diaion WA21J. ► The adsorption equilibrium time of Pt ions was about 20 h. ► The maximum adsorption Q max of Pt ions on the resin based on Langmuir model was 5.69 mg/g at 40 °C. ► Ion exchange was the mechanism involved in the adsorption process of Pt ions. ► The intraparticle diffusion of Pt ions was a main rate-controlling step in most of time of adsorption process.Thermodynamic and kinetics studies for adsorption of Pt ions complexes from the chloride solutions obtained by leaching chlorinated spent automotive catalysts on anionic exchange resin Diaion WA21J were carried out. It was found that only Si, Pt, Rh and Pd from the solution were selectively adsorbed on the resin Diaion WA21J more strongly. The adsorption equilibrium time for Pt ions was about 20 h. The isothermal adsorption of Pt ions was found to fit Langmuir, Freundlich and DKR models. The maximum monolayer adsorption capacities Q max and Xm of Pt ions on the resin based on Langmuir and DKR model were 4.85, 5.36 and 5.69 mg/g as well as 5.01, 5.63 and 5.98 mg/g for temperatures 18 °C, 28 °C and 40 °C, respectively. The apparent adsorption energy E ad based on DKR model were −11.79, −11.04 and −11.04 kJ/mol for the temperatures 18 °C, 28 °C and 40 °C, respectively. Ion exchange was the mechanism involved in the adsorption process. The adsorption of Pt ions on the resin underwent pseudo-first-order kinetic process, and the apparent adsorption activation energy Ea ,1 was 12.6 kJ/mol. The intraparticle diffusion of Pt ions was a main rate-controlling step in most of time of adsorption process.
Keywords: Spent automobile catalyst; Chloride solution; Pt ions; Ion exchange resin; Diaion WA21J; Adsorption;

The phosphate adsorption onto ACF-La was strongly dependent on pH value and the main mechanism involved in adsorption process varied with the change of solution pH. Moreover, high temperature was in favor of the adsorption process. The background electrolyte (NaCl) not only reduced the uptake amount but also increased the effect of intraparticle diffusion on adsorption of phosphate onto ACF-La. Display Omitted► The feasibility of phosphate removal using ACF-La as an adsorbent was investigated. ► The effect of pH on the phosphate adsorption mechanism was identified. ► The effect of ionic strength on the mass transport of phosphate ions onto the ACF-La was examined. ► The behavior of adsorption process by means of evaluating activation energy and thermodynamic parameters was studied.Phosphate removal from polluted water is crucial to preventing eutrophication. Herein, we present the investigation on phosphate adsorption in aqueous solutions by using lanthanum-doped activated carbon fiber (ACF-La). Various batch sorption conditions, e.g., pH, ionic strength, and temperature were tested, and the adsorption mechanisms were discussed. The sorption capacity of ACF-La was higher in acidic solutions than that in basic ones, suggesting that the Lewis acid–base interaction gradually dominated the adsorption process with the increase in pH values. The degree of phosphate removal decreased with the enhancement of the ionic strength of the solution, meaning that the adsorption of phosphate on ACF-La was strongly dependent on ionic strength. Employing the pseudo first- and second-order, and intra-particle diffusion models to evaluate the adsorption kinetics of phosphate onto ACF-La indicated that the second-order model best fits the experimental data. The presence of chloride ion in solutions increased the effect of intra-particle diffusion on the adsorption of phosphate onto ACF-La but reduced the overall rate of the adsorption. The thermodynamic parameters were determined which revealed the feasibility, spontaneity, and endothermic nature of adsorption.
Keywords: Phosphate removal; Activated carbon fiber; Lanthanum; Adsorption; Kinetics;

Two-step resonance energy transfer between dyes in layered silicate films by Juraj Bujdák; Adriana Czímerová; Fernando López Arbeloa (497-504).
Single and two-step FRET between cationic dyes occurs after their concentration on the surface of laponite.Display Omitted► Seven films combining one layered silicate as a carrier and three laser dyes. ► Dye molecular orientation determined by linearly polarized spectroscopy. ► FRET was proven by steady-state and time-resolved fluorescence spectroscopies. ► FRET caused the decrease in fluorescence anisotropy.Single- and two-step fluorescence resonance energy transfer (FRET) was investigated between laser dyes rhodamine 123 (R123), rhodamine 610 (R610), and oxazine 4 (Ox4). The dye molecules played the role of molecular antennas and energy donors (ED, R123), energy acceptors (EA, Ox4), or both (R610). The dye cations were embedded in the films based on layered silicate laponite (Lap) with the thickness of several μm. Optically homogeneous films were prepared directly from dye/Lap colloids. Dye concentration in the films was high enough for FRET to occur but sufficiently low to prevent the formation of large amounts of molecular aggregates. The films were characterized by absorption and fluorescence spectroscopies, and their optical properties were compared with colloid precursors and dye aqueous solutions. The phenomenon of FRET was confirmed by means of steady-state and time-resolved fluorescence spectroscopies. Significant quenching of ED emission in favor of the luminescence from EA molecules was observed. FRET led to the decrease in the lifetimes of excited states of ED molecules. Molecular orientation of dye molecules was determined by polarized absorption and fluorescence spectroscopies. Almost parallel orientation with respect to silicate surface (∼30°) was determined for all fluorescent species of the dyes. Theoretical model on relationship between anisotropy and molecular orientation of the fluorophores fits well with measured data. The analysis of anisotropy measurements confirmed the significant role of FRET in the phenomenon of light depolarization.
Keywords: Fluorescence; Laser dyes; Optical anisotropy; Polarized spectroscopy; Resonance energy transfer; Smectites;

Effect of disjoining pressure on terminal velocity of a bubble sliding along an inclined wall by Lorena A. Del Castillo; Satomi Ohnishi; Lee R. White; Steven L. Carnie; Roger G. Horn (505-511).
In water, bubble slides along glass wall faster than in salt solution.Display Omitted► The terminal velocity of bubble sliding along glass wall varies with salt concentration. ► The first demonstration that terminal velocities of sliding bubble are affected by disjoining pressure. ► Two theories are compared with the experimental results. ► The theoretical comparison suggests that terminal velocities are affected by both hydrodynamic and double-layer forces.The influence of salt concentration on the terminal velocities of gravity-driven single bubbles sliding along an inclined glass wall has been investigated, in an effort to establish whether surface forces acting between the wall and the bubble influence the latter’s mobility. A simple sliding bubble apparatus was employed to measure the terminal velocities of air bubbles with radii ranging from 0.3 to 1.5 mm sliding along the interior wall of an inclined Pyrex glass cylinder with inclination angles between 0.6 and 40.1°. Experiments were performed in pure water, 10 mM and 100 mM KCl solutions. We compared our experimental results with a theory by Hodges et al. which considers hydrodynamic forces only, and with a theory developed by two of us which considers surface forces to play a significant role. Our experimental results demonstrate that the terminal velocity of the bubble not only varies with the angle of inclination and the bubble size but also with the salt concentration, particularly at low inclination angles of ∼1–5°, indicating that double-layer forces between the bubble and the wall influence the sliding behavior. This is the first demonstration that terminal velocities of sliding bubbles are affected by disjoining pressure.
Keywords: Sliding bubble; Terminal velocities; Disjoining pressure; Hydrodynamic forces; Double-layer forces; Electrolyte concentration;

Calculation of contact angle on charged surface by Stephen Chwastiak (512-518).
Sum of calculated contributions to contact angle from three bond types is close to measured contact angle (at pH 5.5).Display Omitted► Contact angle model developed from chemical, hydrophobic and electrostatic reactions. ► Surface chemical data collected at all three interfaces. ► Contact angle calculated from model and data agrees well with measured value.There is good correlation of contact angle measurements and contact angles calculated from surfactant adsorption density data for an electrically neutral surface, as reported in a previous paper for the system hematite–aqueous solution–ketone, with surfactant hexadecyl sulfonic acid. The same method is not sufficient when the hematite surface is electrically charged. Data was collected to develop the appropriate form of an electrostatic term for the analysis. Acid–base titration was used to evaluate surface electrical properties versus pH for the hematite used in the study. Surfactant adsorption isotherms were measured at pH of 4.5, 5.5, 6, and 7 to use in developing an equation for effect of surface potential on contact angle. After adding a term for the contribution of the electric field, the contact angles calculated from adsorption data follow the measured contact angles well.
Keywords: Adsorption isotherms; Surfactants; Contact angle; Wetting; Surface chemistry;

Display Omitted► Immiscible surfactant droplets on thin liquid (‘subphase’) films are studied. ► The ‘near-field’ two-phase flow dynamics are characterized experimentally. ► The ‘far-field’ fingering instability is preceded by subphase trapping and release. ► Subphase expulsion is accompanied by an oscillatory contact line instability.After deposition of immiscible, surface-active liquids on thin liquid films of higher surface tension, Marangoni stresses thin the liquid film around the surfactant droplet and induce a radially outward flow. We observed an oscillatory instability, caused by temporary trapping and subsequent release of subphase liquid from underneath the surfactant droplet. Height profiles of the thin liquid films were monitored using optical interferometry and fluorescence microscopy, both in the vicinity of the deposited surfactant droplet and at larger distances. Numerical calculations based on the lubrication approximation are compared to the experimental results. Good agreement between the experimental and calculated far-field dynamics and values of the spreading exponents was found.
Keywords: Surfactant spreading; Immiscible liquids; Thin liquid films; Oscillatory instability; Marangoni stresses;

Wettability of carbon nanofiber layers on nickel foils by S. Pacheco Benito; L. Lefferts (530-538).
The water contact angle increases with the thickness of the carbon nanofiber layer. The combination of a thick, rough and porous carbon nanofiber layer leads to a super hydrophobic sample.Display Omitted► CNF layers grown on nickel foils. ► Layer thickness has bigger effect on wettability than surface roughness and porosity. ► When CNF layer is thicker than ca. 20 μm, the surface is hydrophobic. ► When the CNF layer is thinner than ca. 20 μm, the surface is hydrophilic.Carbon nanofiber (CNF) layers have been directly synthesized on nickel foils by chemical vapor deposition at 450 °C using different H2 concentrations and reaction times. The addition of 5% H2 produces thicker, rougher and more porous CNF layers than when 1% H2 is used. The roughness and porosity increases with reaction time when 5%, 10% or 20% H2 are used; however, this effect is less pronounced when 1% H2 is used. CNFs are 50–55 nm in diameter and have a fishbone type structure. We have studied the influence of CNF layer thickness, porosity and surface roughness on the interaction with water by measuring the contact angle. The water wetting properties of the samples are more significantly influenced by the CNF layer thickness than both surface roughness and porosity. When the CNF layer is thicker than ca. 20 μm, the surface is hydrophobic and the contact angle increases with surface roughness and porosity. When the CNF layer is thinner than ca. 20 μm, the surface is hydrophilic and the contact angle decreases with increasing surface roughness and porosity. This behavior is attributed to penetration of water, making contact with the hydrophilic C layer between the CNF layer and the foil.
Keywords: Carbon nanofibers; Layer; Wettability; Contact angle; Roughness; Porosity;

Complex layering observed in high internal phase emulsions at a silicon surface by neutron reflectometry by Philip A. Reynolds; Mark J. Henderson; Johann Zank; John W. White (539-545).
Neutron reflectometry reveals layering when emulsions contact a silicon surface.Display Omitted► Emulsions can spontaneously form layers at a silicon surface. ► The more hydrophilic the surfactant used, the more the number of layers. ► The layers resemble sections of lamellar bulk phases. ► This surface behaviour follows the trends in bulk emulsion phases.The neutron reflectivity profiles from the interface between silicon and aqueous phase-in-oil high internal phase emulsions of steadily increasing surfactant hydrophilicity, are reported for two isotopic contrasts for each surfactant. Layered models are required to fit the structured reflectivity profiles that demonstrate that the oxidised top layer of the silicon is always covered by a surfactant monolayer. Interposed between the surfactant monolayer and the bulk emulsion is a layer of oil – a geometric effect caused by reorganisation of the aqueous droplets. As the surfactant hydrophilicity increases, alternating aqueous and oil + surfactant layers are inserted between this topmost oil layer and the oxide attached surfactant monolayer. The resulting structures have compositions and layer spacings suggestive of sections from lamellar phases. This increase in layer ordering with increasing surfactant hydrophilicity is expected. The bulk emulsions are observed to exhibit lamellar or sponge phases increasingly as surfactant hydrophilicity increases.
Keywords: Neutron reflectivity; Emulsions; Lamellae; Surface layers;

Sub-minute formation of supported nanoporous mesoscale patterns programmed by surface energy by Venumadhav Korampally; Vamshi Krishna Mamidi; Bryant Harris; Keshab Gangopadhyay; Gary A. Baker; Shubhra Gangopadhyay (546-554).
The authors demonstrate a novel concept of using chemically patterned substrates to control nanoscale structural organization within organosilicate nanoparticle films. The principle behind the behavior of the system is explained by taking into consideration the entropic and enthalpic interplay between the substrate surface chemical functionality, polymer and the dispersed nanoparticles. The relevance of this research is shown by demonstrating that the principle of surface energy gated nanostructure may be utilized to achieve spontaneously patterned spatial regions of nanoporous, high surface area thin films.Display Omitted► Substrate surface energy dictates thin film nanostructure. ► Nanoparticle–polymer systems above decomposition temperature of polymer. ► Entropy–enthalpy interplay between nanoparticles, polymer and substrate surface. ► Chemically patterned substrates used for spontaneous patterning of nanoporous films. ► Ensemble behavior of the nanoparticles studied using Ellipsometry.We demonstrate an original and powerful concept for elaborating spontaneous, high fidelity patterns of nanoporosity from nanoscale building blocks using patterned surface chemistry (i.e., “surface energy gating”) to corral the growth of colloidal structures at a solid surface. Composite films consisting of polymethylsilsesquioxane nanoparticles uniformly dispersed in polypropylene glycol polymer were examined at temperatures beyond the decomposition of the polymer as a function of the substrate surface energy to clarify nanoparticulate ensemble behavior. The principle behind this colloidal assembly can be understood by taking into consideration the entropy and enthalpy dictating the mutual interactions between substrate surface, polymeric solvent, and dispersed colloids in the decomposition regime. The relevance of this research is shown by demonstrating how the principle of surface energy gating can be utilized to achieve spontaneous and controllable spatial patterns of nanoporous, high surface area thin films in a cost-effective and energy-efficient manner via brief thermal exposure. The simplicity and general nature of this methodology are further exemplified by showing the facility with which high-contrast fluorescent bioconjugate arrays can be prepared from nanoporous organosilicate patterns.
Keywords: Patterning; Surface energy; Nanoporous films; Nanoparticle–polymer systems; Entropy; Enthalpy;

Controllable fabrication of porous free-standing polypyrrole films via a gas phase polymerization by Junyu Lei; Zhicheng Li; Xiaofeng Lu; Wei Wang; Xiujie Bian; Tian Zheng; Yanpeng Xue; Ce Wang (555-560).
We report a facile and an efficient way to fabricate large-area porous free-standing polypyrrole films by a vapor phase polymerization in the pyrrole gas/water interface. The method was extraordinarily simple and the film could be easily peeled off. Furthermore, both the thickness of the film and the size of the pores could be controlled by adjusting the concentrations of the oxidant and the reaction time. The thickness could be controlled from 5 to 23 μm, whereas the pores were controlled in diameters ranging from 1.3 to 7.2 μm. The porous free-standing PPy films exhibit superhydrophilic behavior due to their composition and porous structure.Display Omitted► Porous free-standing PPy films are obtained in the gas/water interface through the interface polymerization. ► Both the thickness of the film and the size of the pores could be controlled. ► The PPy films exhibited a superhydrophilic behavior.A facile gas phase polymerization method has been proposed in this work to fabricate porous free-standing polypyrrole (PPy) films. In the presence of pyrrole vapor, the films are obtained in the gas/water interface spontaneously through the interface polymerization with the oxidant of FeCl3 in the water. Both the thickness of the film and the size of the pores could be controlled by adjusting the concentrations of the oxidant and the reaction time. The as-prepared PPy films exhibited a superhydrophilic behavior due to its composition and porous structures. We have demonstrated a possible formation mechanism for the porous free-standing PPy films. This gas phase polymerization is shown to be readily scalable to prepare large area of PPy films.
Keywords: Polypyrrole; Free-standing films; Porous films; Vapor phase polymerization.;

Display Omitted► Silica coated layers with different morphologies are prepared by electrospraying. ► Precursor solutions of low viscosity deposit particulated silica layers, exhibiting superhydrophobicity. ► In contrast, fibrous silica layers that show superhydrophilicity are attained with viscous precursor solutions. ► The dramatic change in the water contact angle without any chemical treatment is useful in many applications.Silica layers with different microstructures were prepared by electrospraying. The microstructure of the layers was changed by controlling the viscosity of the precursor solutions in the electrospray deposition. Precursor solutions of low viscosity produced particulated silica layers, exhibiting superhydrophobicity. In contrast, fibrous silica layers exhibiting superhydrophilicity were attained with viscous precursor solutions. In particular, the particulated silica layers showed a good durability and resistance to ultraviolet illumination. The dramatic change in the wettability of silica layers without any chemical treatment is promising in speeding up their use in many fields.
Keywords: Silica; Electrospray; Hydrophobicity; Hydrophilicity; Microstructure;

Novel supramolecular gelation route to in situ entrapment and sustained delivery of plasmid DNA by Dong Ma; Hong-Bin Zhang; Di-Hu Chen; Li-Ming Zhang (566-573).
For the plasmid DNA complexes released from the supramolecular hydrogel, they could show sustained gene transfection property.Display Omitted► Novel supramolecular gelation route was developed for in situ encapsulation and sustained release of plasmid DNA. ► The in situ encapsulation of plasmid DNA into the supramolecular hydrogel matrix could be carried out under mild conditions. ► The resultant supramolecuar hybrid hydrogel has adjustable gelation time and mechanical strength.In this work, cationic block copolymer (F-68-PLL) composed of Pluronic F-68 and poly(l-lysine) segments was first prepared for the binding with plasmid DNA due to the electrostatic interaction between poly(l-lysine) segments and plasmid DNA, and subsequently used to interact with α-cyclodextrin (α-CD) in aqueous system for the supramolecular gelation by the inclusion complexation between Pluronic F-68 segments and α-CD. It was found that such a fabrication process could lead to the in situ entrapment of plasmid DNA into the supramolecular hydrogel matrix under mild conditions. Depending on the amounts of F-68-PLL and α-CD, the resultant hybrid hydrogel was found to have adjustable gelation time and mechanical strength. For the plasmid DNA complexes released from the supramolecular hydrogel, controlled release and sustained gene transfection were confirmed.
Keywords: Supramolecular gelation; Plasmid DNA; In situ entrapment; Sustained delivery;

Air-stable silver-coated copper particles of sub-micrometer size by D.S. Jung; H.M. Lee; Y.C. Kang; S.B. Park (574-581).
Air-stable copper particles of submicrometer size were prepared by coating silver in a one-step spray pyrolysis reactor. Color of copper particles remained unchanged for all levels of silver loading up to 250 °C. Sheet resistance of coated particles was decreased due to lack of oxide layer on copper particles and low sintering temperature of coated silver. Microstructures of conductive film are consistent with the measurement of resistivity.Display Omitted► The silver coated copper particles were formed by the segregation of silver phase. ► Enhanced air-stability was confirmed by color, sheet resistance, TG, XRD and HRTEM. ► The thin coated-silver contributed to formation of dense conductive film.Silver-coated copper particles with various silver loading were prepared by a direct liquid-to-particle conversion process in spray pyrolysis reactor system. The prepared particles were completely densified at 900 °C within a residence time of 2.1 s and had core–shell structure, of which formation mechanism was proposed. The mean diameter of particles was 0.45 μm. Copper particles of 20 wt.% of silver loading were stable under air and 95% of copper remained as metallic copper even after 1 month of exposure to air. This enhanced air-stability contributed to the enhanced electrical property of conductive film obtained from the coated particles. The conductive film obtained from 15 wt.% of silver-coated copper particles had a sheet resistance of 1.2 mΩ square−1. This low resistance resulted from the lack of oxide layer and low sintering temperature of silver layer.
Keywords: Copper particles; Air-stability; Coating; Conductive film; Spray pyrolysis;

Imaging of blood plasma coagulation at supported lipid membranes by Lars Faxälv; Jasmin Hume; Bengt Kasemo; Sofia Svedhem (582-587).
Time-lapse imaging of blood plasma coagulation at SiO2 substrate and POPS(30%)/POPC(70%) lipid membrane.Display Omitted► The imaging setup offers a flexible solution for coagulation studies at membranes. ► The imaging method gives at hand novel information about the coagulation process. ► The method can be modified to study activity of specific enzymes on membranes.The blood coagulation system relies on lipid membrane constituents to act as regulators of the coagulation process upon vascular trauma, and in particular the 2D configuration of the lipid membranes is known to efficiently catalyze enzymatic activity of blood coagulation factors. This work demonstrates a new application of a recently developed methodology to study blood coagulation at lipid membrane interfaces with the use of imaging technology. Lipid membranes with varied net charges were formed on silica supports by systematically using different combinations of lipids where neutral phosphocholine (PC) lipids were mixed with phospholipids having either positively charged ethylphosphocholine (EPC), or negatively charged phosphatidylserine (PS) headgroups. Coagulation imaging demonstrated that negatively charged SiO2 and membrane surfaces exposing PS (obtained from liposomes containing 30% of PS) had coagulation times which were significantly shorter than those for plain PC membranes and EPC exposing membrane surfaces (obtained from liposomes containing 30% of EPC). Coagulation times decreased non-linearly with increasing negative surface charge for lipid membranes. A threshold value for shorter coagulation times was observed below a PS content of ∼6%. We conclude that the lipid membranes on solid support studied with the imaging setup as presented in this study offers a flexible and non-expensive solution for coagulation studies at biological membranes. It will be interesting to extend the present study towards examining coagulation on more complex lipid-based model systems.
Keywords: Coagulation; Platelet phospholipids; Imaging; Supported lipid membrane; Surface charge; Zeta-potential;

Induced-charge electrokinetic flow over an electrically conducting surface in a microchannel will generate vortices, which can be used to adjust the flow rates and the concentration. By using appropriate size of the conducting surfaces in appropriate locations, the microfluidic system can generate not only streams of the same flow rate or linearly decreased flow rates in different channels, but also different, uniform concentrations within a short mixing length quickly. Concentration distribution under electric field of 50 V/cm. Thicker lines indicate conducting surfaces. Because of the vortices generated in the flow field, three uniform and different concentrations are generated in three branches in less than 1.0 s.Display Omitted► Induced-charge electrokinetic flow in microfluidic channel. ► Generates equivalent or linear flow rates in three streams. ► Generates equal concentration in three streams. ► Generate different concentrations in three streams. ► Simple structure and high efficiency.This paper presents a numerical study of controlling the flow rate and the concentration in a microchannel network by utilizing induced-charge electrokinetic flow (ICEKF). ICEKF over an electrically conducting surface in a microchannel will generate vortices, which can be used to adjust the flow rates and the concentrations in different microchannel branches. The flow field and concentration field were studied under different applied electric fields and with different sizes of the conducting surfaces. The results show that, by using appropriate size of the conducting surfaces in appropriate locations, the microfluidic system can generate not only streams of the same flow rate or linearly decreased flow rates in different channels, but also different, uniform concentrations within a short mixing length quickly.
Keywords: Microfluidic system; Mixing enhancement; Induced-charge electrokinetic flow; Vortex; Flow rate; Concentration difference;

Controlling the primary particle evolution process towards silica monoliths with tunable hierarchical structure by Yu Zhou; Wei Gang Lin; Jing Yang; Ling Gao; Na Lin; Jia Yuan Yang; Qian Hou; Ying Wang; Jian Hua Zhu (594-604).
Hierarchical mesoporous silica monoliths with high mechanical intensity, tunable 3D net-liked framework and textural properties were synthesized in hydroxyl carboxylic acids route.Display Omitted► Using hydroxyl carboxylic acids to create a weak acidic synthetic condition. ► Adjusting the resembling process of micro-morphology to mesostructure. ► Hierarchical monoliths exhibit a high mechanical strength up to 25 N cm−2. ► Efficiently eliminate particulate matters and tobacco special nitrosamines in smoke.In order to establish the hierarchical structure in multiple levels on mesoporous silica, this article reports a new strategy to prepare the monolith with the pore configuration in nanometer scale, micro-morphology in micrometer level and macroscopic shape in millimeter or larger grade. These hierarchical monoliths are synthesized in a weak acidic condition by using triblock copolymer P123, hydroxyl carboxylic acid and tetramethyl orthosilicate (TMOS), and the textural properties of the mesostructure can be facilely adjusted by simply controlling the synthesis condition without any additive. During the synthesis, the primary particles can be selectively synthesized as monodispersed sphere, noodle, prism, straight rods with different size or irregular bars, and their connection plus arrangement in 3D directions can be also regulated. Therefore, various textural properties of mesopore are able to be altered including pore size (5.5–10.6 nm), total pore volume (0.48–1.2 cm3  g−1), micropore surface area (47–334 m2  g−1), and pore shape (from 2D or 3D straight channel to plugged channel). Moreover, these monoliths exhibit a considerable mechanical strength; they are also applied in eliminating particulate matters and tobacco special nitrosamines (TSNA) in tobacco smoke, exhibiting various morphology-assisted functions.
Keywords: Hierarchical mesoporous silica monolith; Delayed reflecting process; Weak acidic synthesis using hydroxyl carboxylic acid; High mechanical strength; Environment protection;