Journal of Colloid And Interface Science (v.358, #1)

Cover 1 (OFC).

(a) At 0 V, the difference in adhesive force caused by the liquid mediated meniscus (b) between the three samples is small. When voltage is applied, the electric field-induced meniscus (c) exists for samples 2 and 3 only and results in a considerable increase in adhesive force.Display Omitted► We investigate the physics of different stiction mechanisms in electrostatic MEMS. ► We study stiction caused by dielectric charging, water meniscus and their interaction. ► The electric field-induced meniscus is the dominant mechanism at higher humidity. ► For the annealed samples and at low humidity the field-induced meniscus is reduced. ► The evolution of adhesive force with time is used to study the dielectric charging.In this work, for the first time different stiction mechanisms in electrostatic micro-electromechanical systems (MEMS) switches were studied. In these devices stiction can be caused by two main mechanisms: dielectric charging and meniscus formation resulting from the adsorbed water film between the switch bridge and the dielectric layer. The effect of each mechanism and their interaction were investigated by measuring the adhesive and friction forces under different electrical stress conditions and relative humidity levels. An atomic force microscope (AFM) was used to perform force–distance and friction measurements on the nanoscale. A novel technique was proposed to measure the induced surface potential over the dielectric surface and was used to explain the obtained adhesive and friction results. The evolution of adhesive force with time was monitored in order to study the charging/discharging processes in the dielectric film. The assessment methodology is employed for application in RF-MEMS switches and could be extended to other electrostatic MEMS devices. The study provides an in-depth understanding of different stiction mechanisms, and explanation for the literature reported device level measurements for electrostatic capacitive MEMS switches.
Keywords: Stiction; Dielectric charging; Field-induced meniscus; RF-MEMS switch; Adhesion and friction; Nanoscale characterization; Force–distance measurements; Electrostatic actuation;

Immobilized PEO–polybutadiene–PEO triblocks on medical polymers support the integration of small biofunctional peptides such as nisin, without compromising anti-fouling activity against large blood proteins.Display Omitted► Nisin, a small antimicrobial polypeptide, becomes integrated in pendant PEO layers. ► Entrapment within pendant PEO layers enhances resistance of nisin to elution. ► Nisin-loaded PEO layers retain their ability to prevent adsorption of fibrinogen. ► Robust principal components analysis distinguishes proteins and detects outliers.Stable, pendant polyethylene oxide (PEO) layers were formed on medical-grade Pellethane® and Tygon® polyurethane surfaces, by adsorption and gamma-irradiation of PEO–polybutadiene–PEO triblock surfactants. Coated and uncoated polyurethanes were challenged individually or sequentially with nisin (a small polypeptide with antimicrobial activity) and/or fibrinogen, and then analyzed with time-of-flight secondary ion mass spectrometry (TOF-SIMS). Data reduction by robust principal components analysis (PCA) allowed detection of outliers, and distinguished adsorbed nisin and fibrinogen. Fibrinogen-contacted surfaces, with or without nisin, were very similar on uncoated polymer surfaces, consistent with nearly complete displacement or coverage of previously-adsorbed nisin by fibrinogen. In contrast, nisin-loaded PEO layers remained essentially unchanged upon challenge with fibrinogen, suggesting that the adsorbed nisin is stabilized within the pendant PEO layer, while the peptide-loaded PEO layer retains its ability to repel large proteins. Coatings of PEO loaded with therapeutic polypeptides on medical polymers have the potential to be used to produce anti-fouling and biofunctional surfaces for implantable or blood-contacting devices.
Keywords: Nisin; Fibrinogen; TOF-SIMS; Protein adsorption; Medical polymers; PEO polybutadiene–PEO triblock surfactants; Robust PCA;

Amplitude sweeps showing storage (G′) and loss (G″) modulus of barrier coatings containing clay of different shape factor at the same solids concentration.Display Omitted► Critical strain correlated with the reverse of clay shape factor. ► A clay with high shape factor gives a lower critical strain. ► A clay of high shape factor show a lower water vapour transmission rate.Oscillatory shear rheology of barrier coatings based on dispersed styrene–butadiene latex and clay of various shape factors or aspect ratio has been explored. Barrier performance of these coatings when applied to paperboard has been assessed in terms of water vapour transmission rates and the results related to shape factor, dewatering and critical strain. It has been shown that a system based on clay with high shape factor gives a lower critical strain, dewatering and water vapour transmission rate compared with clays of lower shape factor. The dissipated energy, as calculated from an amplitude sweep, indicated no attractive interaction between clay and latex implying a critical strain that appears to be solely dependent on the shape factor at a constant volume fraction. Particle size distribution was shown to have no effect on the critical strain while coatings of high elasticity exhibited high yield strains as expected. The loss modulus demonstrated strain hardening before the elastic to viscous transition. The loss modulus peak was identified by a maximum strain which was significantly lower for a coating based on clay with a high shape factor. The characteristic elastic time was found to vary between 0.6 and 1.3 s. The zero shear viscosity of barrier dispersion coatings were estimated from the characteristic elastic time and the characteristic modulus to be of the order of 25–100 Pa s.
Keywords: Rheology; Clay; Shape factor; Aspect ratio; Water vapour transmission rate; Dewatering; Moisture barrier coating;

Luminescent silicate core–shell nanoparticles: Synthesis, functionalization, optical, and structural properties by Sofia Dembski; Sabine Rupp; Carsten Gellermann; Miroslaw Batentschuk; Andres Osvet; Albrecht Winnacker (32-38).
Redispersible luminescent SiO2/Zn2SiO4:Mn2+ core–shell nanoparticles with sizes in the range of 55–220 nmDisplay Omitted► Redispersible luminescent SiO2/Zn2SiO4:Mn2+ core–shell nanoparticles. ► Synthesis via sol–gel process followed by annealing at high temperatures. ► Adjustable particle sizes of 55–220 nm. ► Possibility to control the crystal structure and optical properties of nanoparticles. ► Surface modification in accordance with the intended application.SiO2/Zn2SiO4:Mn2+ core–shell nanoparticles with mean diameters in the range of 55–220 nm were prepared by a modified Pechini sol–gel method followed by lyophilization and annealing at temperatures of 800–1100 °C. The as-synthesized nanoparticles were characterized by transmission electron microscopy, X-ray diffraction analysis, and photoluminescence spectroscopy. The results demonstrate that the crystal structure of the shell and the optical properties can be tuned by the annealing temperature and a variation of the concentration of doping ions. Under UV excitation, the samples emit green luminescence with its maximum at 525 nm, typical for the Mn2+ ions in α-Zn2SiO4. The resulting nanoparticles were successfully modified with amine and carboxyl functions with respect to a later attachment of biological moieties.
Keywords: Nanophosphor; Luminescent core–shell nanoparticles; Zn2SiO4;

Structure and morphology of spinel MFe2O4 (M = Fe, Co, Ni) nanoparticles chemically synthesized from heterometallic complexes by Karine Priscila Naidek; Flavia Bianconi; Tulio Costa Rizuti da Rocha; Daniela Zanchet; Juliano Alves Bonacin; Miguel Alexandre Novak; Maria das Graças Fialho Vaz; Herbert Winnischofer (39-46).
Solvothermal decomposition of trimetallic acetate complexes is a synthetic procedure to obtain spinel ferrite nanoparticles with controlled size and composition.Display Omitted► Iron acetate and its derivatives are good precursors to spinel ferrite NP. ► The precursor influences the morphology of the NP, but not the composition. ► The morphology of spinel ferrite nanoparticles influences its magnetic properties.We synthesized magnetic spinel ferrites from trimetallic single-source precursors. Fe(II), Co(II), and Ni(II) ferrite nanoparticles in the range of 9–25 nm were synthesized by solvothermal decomposition of trimetallic acetate complex precursors in benzyl ether in the presence of oleic acid and oleylamine, using 1,2-dodecanediol as the reducing agent. For comparison, spinel ferrite nanoparticles were synthesized by stoichiometric mixtures of metal acetate or acetylacetonate salts. The nanoparticles (NP) were characterized by TEM, DLS, powder XRD, and Raman spectroscopy; and their magnetic properties were characterized by ZFC–FC and M(H) measurements. The ferrite-NP were more homogeneous and had a narrower size distribution when trimetallic complexes were used as precursors. As a consequence, the magnetic properties of these ferrite-NP are closer to the aimed room temperature superparamagnetic behavior, than are those of other ferrites obtained by a mixture of salts.
Keywords: Spinel; Nanoparticle; Nanocrystal; Monodisperse; Heterometallic complexes; Solvothermal; Chemical synthesis; Superparamagnetic;

Negligible absorption of radiofrequency radiation by colloidal gold nanoparticles by Dongxiao Li; Yun Suk Jung; Susheng Tan; Hong Koo Kim; Eamon Chory; David A. Geller (47-53).
The radiofrequency heating of gold nanoparticle colloidal solutions is found to be due to the Joule heating of ionic solution, not due to RF energy absorption of gold nanoparticles.Display Omitted► Gold nanoparticles were physically separated from the Au-NP colloidal solutions by centrifugation. ► RF heating and electrical conductivity measurements were performed. ► RF heating of colloidal solutions is caused by ionic conduction Joule heating of background solution. ► Au nanoparticles do not contribute to RF energy absorption.We report quantitative measurement of heat generation in Au-nanoparticle colloidal solutions induced by radiofrequency (RF) electromagnetic waves (13.56 MHz; 25 W). The possible role of Au nanoparticles in RF heating was systematically investigated by separating the metal nanoparticles away from the colloidal solutions by centrifugation. Contrary to the previously made assumption in this field, it is found that Au nanoparticles do not contribute to RF energy absorption. The electrical conductivity measurement of the solutions with and without Au nanoparticles reveals that the Joule heating via ionic conduction in the electrolyte solutions is the dominant mechanism of RF-radiation-to-thermal conversion.
Keywords: Gold nanoparticles; Colloidal solutions; Radiofrequency heating; Ionic conduction; Plasmon resonance;

The synthesized Fe3O4@Ag nanoparticles with an average of 27 nm particle size and 25 nm surface roughness could be used as active SERS substrates for Cr(VI) determination.Display Omitted► A simple process was introduced to synthesize Fe3O4@Ag magnetic nanostructures. ► The SERS substrate can adsorb Cr(VI) and substantially enhance Raman signal. ► Determination of Cr(VI) was achieved using a portable Raman spectrometer.A novel sensitive and recyclable SERS substrate which can actively concentrate chromate (Cr(VI)) in water and substantially enhance Raman signal was synthesized as uniform Fe3O4@Ag nanoparticles. The surface morphology, structure, and magnetic properties were characterized using transmission electron microscopy, atomic force microscopy, X-ray powder diffraction, X-ray photoelectron spectroscopy, and vibrating sample magnetometry analysis. The closely spaced Fe3O4@Ag substrate with a core–shell structure exhibited a 25 nm surface roughness. The high saturation magnetization at 48.35 emu g−1 enabled the complete and rapid separation of the substrate from the solution. The sensitivity and reproducibility of the substrate were confirmed using a common SERS probe molecule, rhodamine 6G. SERS spectra of Cr(VI) in simulated and real contaminated water showed that the symmetric stretching vibrations of Cr–O occurred at 796 cm−1. This SERS peak area exhibited a linear dependence (R 2  = 0.9992) on the Cr(VI) concentration between 5 and 100 μg L−1. Coexisting anions such as sulfate, nitrate, chloride, carbonate, and humic acid could decrease the sensitivity of the SERS analysis. However, the adverse effect of the competing ions may be eliminated by proper dilution of the raw sample. This study provides a reliable method for qualitative and quantitative analysis of Cr(VI).
Keywords: SERS; Fe3O4@Ag; Characterization; Cr(VI) determination; Coexisting ions interference;

Experimental study of electrostatically stabilized colloidal particles: Colloidal stability and charge reversal by Christian Schneider; Mathias Hanisch; Bastian Wedel; Arben Jusufi; Matthias Ballauff (62-67).
ζ Potential and diffuse potential Ψ d of anionic, surface charged colloids as a function of the concentration of lanthanum ions. The results show charge reversal (cr) beyond the critical coagulation concentration (ccc) together with a comparison to the classical Poisson–Boltzmann theory (dashed line).Display Omitted► We measure the weak repulsion of charged colloidal spheres near charge reversal. ► We combine for the first time microsurface potential measurements with measurements of the zeta potential under identical conditions. ► We determine and discuss the critical coagulation concentration and the concentration of charge reversal of a model system. ► We discuss the implications of our findings for the DLVO theory. ► We demonstrate that adsorption of multivalent ions is the major cause for destabilization of colloidal particles in the presence of multivalent ions.We consider the interaction of colloidal spheres in the presence of mono-, di-, and trivalent ions. The colloids are stabilized by electrostatic repulsion due to surface charges. The repulsive part of the interaction potential Ψ d is deduced from precise measurements of the rate of slow coagulation. These “microsurface potential measurements” allow us to determine a weak repulsion in which Ψ d is of the order of a few k B T. These data are compared to ζ potential measured under similar conditions. At higher concentrations both di- and trivalent counterions accumulate at the very proximity of the particle surface leading to charge reversal. The salt concentration c cr at which charge reversal occurs is found to be always above the critical coagulation concentration c ccc . The analysis of Ψ d and of the ζ potential demonstrates, however, that adsorption of multivalent counterions starts far below c cr . Hence, colloid stability in the presence of di- and trivalent ions cannot be described in terms of a DLVO ansatz assuming a surface charge that is constant with regard to the ionic strength.
Keywords: DLVO theory; Zeta potential; Diffuse potential; Colloidal stability; Charge reversal; Charge inversion; Multivalent counterions; Microsurface potential measurements; Counterion adsorption; Counterion correlations; Poisson–Boltzmann; Simultaneous static and dynamic light scattering; Electrostatic stabilization;

SrTiO3 hollow microspheres built by nanocubes were synthesized by hydrothermal method. Owing to the special hollow structure, the synthesized SrTiO3 microspheres exhibit a superior photocatalytic activity in photoreduction of Cr(VI).Display Omitted► Hierarchical SrTiO3 hollow microspheres were synthesized. ► Microspheres were assembled by nanocubes. ► The sample exhibits a superior photocatalytic activity. ► The activity is due to the hierarchical hollow structure. ► In situ phase transition from anatase to titanate is relatively easy.SrTiO3 hollow microspheres built by regular nanocubes were synthesized by a general and facile hydrothermal method. The resulting samples were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD) measurements. Owing to the special hollow structure, the synthesized SrTiO3 microspheres exhibit a superior photocatalytic activity in photoreduction of Cr(VI). As anatase and titanate contain common structural features, it makes this in situ phase transition from anatase to titanate relatively easy. Therefore, this method is rather convenient for controlling the morphology of the products by varying the presynthesized anatase TiO2 precursor.
Keywords: Photocatalyst; SrTiO3; Hollow microspheres; Nanocubes; Photoreduction;

Preparation of quantum dots encoded microspheres by electrospray for the detection of biomolecules by Lei Sun; Xiaofang Yu; Mingda Sun; Hengguo Wang; Shufei Xu; John D. Dixon; Y. Andrew Wang; Yaoxian Li; Qingbiao Yang; Xiaoyi Xu (73-80).
Quantum dots encoded microspheres were prepared by electrospray for the fluoroimmunoassays between antigens of the mouse IgG and FITC labeled antibodies of the goat–anti-mouse IgG.Display Omitted► Polystyrene microspheres with QDs of various colors were prepared by electrospray technology. ► Immunofluorescence analysis was carried out in experiment. ► The technology could be also suitable for encapsulating other optical and magnetic nanoparticles.In this paper, a novel method based on the electrospray technique has been developed for preparation of quantum dot (QD)-encoded microspheres for the fist time. By electrospraying the mixture of polymer solution and quantum dots solution (single-color QDs or multi-color QDs), it is accessible to obtain a series of composite microspheres containing the functional nanoparticle. Poly(styrene–acrylate) was utilized as the electrospray polymer materials in order to obtain the microsphere modified with carboxyl group on the surface. Moreover, to test the performance of the QD-encoded microsphere in bioapplication, it is carried out that immunofluorescence analysis between antigens of mouse IgG immobilized on the functional microsphere and FITC labeled antibodies of goat–anti-mouse IgG in experiment. To the best of our knowledge, this is the first report of QD-encoded microspheres prepared by electrospray technology. This technology can carry out the one-pot preparation of different color QD-encoded microspheres with multiple intensities. This technology could be also suitable for encapsulating other optical nanocrystals and magnetic nanoparticles for obtaining multifunctional microspheres. All of the results in this paper show that the fluorescence beads made by electrospray technique can be well applied in multiplex analysis. These works provide a good foundation to accelerate application of preparing microspheres by electrospray technique in practice.
Keywords: Electrospray technique; QD-encoded microspheres; Immunofluorescence;

Shape-specific nanofibers via self-assembly of three-branched peptide by Tomoyuki Koga; Harunobu Matsui; Takahiro Matsumoto; Nobuyuki Higashi (81-85).
A novel amphiphilic three-armed peptide, in which three β-sheet formable peptides (L4K8L4) were connected by Lys residue, showed the pH-dependent self-assembly into shape-specific nanofibers with morphologically kinked structures.Display Omitted► A novel amphiphilic branched peptide containing three β-sheet formable peptides was newly prepared as a building block for self-assembly. ► Conformation of the branched peptide could be easily controlled by manipulating the solution pH. ► The branched peptide was found to form a shape-specific β-sheet-based nanofiber with morphologically kinked structure via self-assembly.A novel amphiphilic branched peptide (1), in which three β-sheet formable peptides (L4K8L4) were connected by Lys residue, was newly prepared as a building block for self-assembly. A detailed analysis of the conformation and self-assembling property of 1 in water at various pH conditions was performed by using circular dichroism, FTIR, atomic force and transmission electron microscopies. The experimental results revealed that the branched peptide showed a pH-dependent conformation forming a shape-specific β-sheet-based nanofiber with morphologically kinked structures under specific pH conditions. Exploring a novel peptide building unit that has the ability to self-assemble into designed and complicated nano-objects is valuable to facilitate a bottom-up nanotechnology.
Keywords: Self-assembly; Three-branched peptide; Nanofiber; β-Sheet structure; Shape-specificity;

Deoxycholate as an efficient coating agent for hydrophilic silicon nanocrystals by Elena Froner; Elvira D’Amato; Roberta Adamo; Nikola Prtljaga; Silvia Larcheri; Lorenzo Pavesi; Adelio Rigo; Cristina Potrich; Marina Scarpa (86-92).
Water soluble, light emitting silicon nanocrystals were obtained by a two-step procedure: a chemical grafting followed by physical coating by deoxycholate which is natural surfactant-like molecule well tolerated by cells. This compound maintained the bright nanocrystal luminescence emission stable for 4–5 days.Display Omitted► Stable aqueous solutions of luminescent silicon nanocrystals are obtained by a two-step procedure. ► The first step consists in the grafting of alkyl chains on nanocrystal surface. ► The second step consists in the physical coating of nanocrystals by a surfactant. ► Deoxycholic acid is a mild surfactant present in human intestine. ► Deoxycholic acid is well tolerated by cells and living organisms.Silicon nanocrystals were made hydrophilic by 10-undecenoic acid grafting and were then coated with sodium deoxycholate, a detergent-like compound belonging to the bile acid class which is crucial for absorption of lipids in the small intestine. The resulting silicon nanocrystals have an average diameter of 3–5 nm, can be dispersed in aqueous solutions and show stable photoluminescence. Coating with non-biological surfactants, which are dangerous for cell safety, was investigated for comparison. Results indicate that deoxycholate is a stabilizer of luminescent silicon nanocrystals. Deoxycholate coated nanocrystals appear suitable for applications as multifunctional probes in biomedicine.
Keywords: Silicon nanocrystals; Luminescence; Surfactant; Deoxycholate;

Self-assembly behavior and photoluminescence property of bispyrenyl-POSS nanoparticle hybrid by Chu-Hua Lu; Chia-Hua Tsai; Feng-Chih Chang; Kwang-Un Jeong; Shiao-Wei Kuo (93-101).
Two flexible ether bonds were designed to connect two pyrene rings on a polyhedral oligomeric silsesquioxane (BPy-POSS) to enrich the fraction of “intrinsic intramolecular pyrene-dimer” on the surface of crystal isobutyl-POSS (iBu-POSS) thin-films.Display Omitted► We synthesized two flexible ether bonds to connect two pyrene rings on POSS. ► We observe the significantly enhancement the intrinsic intramolecular pyrene dimer fraction on POSS surface. ► We discussed the emission spectra of BPy-POSS and its application for chemosensor.Two flexible ether bonds were designed to connect two pyrene rings on a polyhedral oligomeric silsesquioxane (BPy-POSS) to enrich the fraction of “intrinsic intramolecular pyrene-dimer” on the surface of crystal isobutyl-POSS (iBu-POSS) thin-films. Compared to the monomer emission of 1-pyrenemethanol (Py-OH), the emission spectra of BPy-POSS in dichloromethane show the large proportion of intramolecular and intermolecular excimers due to the formation of pyrenyl dimers or aggregates via the easy rotation of two adjacent ether bonds and the π–π interaction of pyrene rings, respectively. By blending inert iBu-POSS, the fluorescent dimers or aggregates of 5 wt.% and 20 wt.% BPy-POSS are distributed on the surface of iBu-POSS crystal fractal pattern as shown by confocal photoluminescence microscopy. Upon exposure to the vapors of nitrobenzene, the 5 wt.% BPy-POSS blend shows the similar quenching efficiency as 100 wt.% BPy-POSS blends, indicating the better excimer dispersion for vapor permeability of blend thin-films.
Keywords: Polyhedral oligomeric silsesquioxane; Nanocomposites; Photoluminescence; Self-assembly;

Spinel ZnFe2O4 nanospheres were synthesized in high yield via a general, one-step and template-free solvothermal route. The sphere-like ZnFe2O4 showed dramatically enhanced photocatalytic degradation of rhodamine B.Display Omitted► Sphere-like ZnFe2O4 nanostructures are successfully synthesized via a facile method. ► The structural properties for the promoted photocatalytic performance are discussed. ► The sphere-like ZnFe2O4 shows enhanced photocatalytic degradation of rhodamine B. ► Hydroxyl radicals play an important role in the photocatalytic degradation of rhodamine B.Spinel zinc ferrite nanospheres with diameters of about 212 nm were synthesized in high yield via a general, one-step and template-free solvothermal route. The prepared nanospheres had cubic spinel structure and exhibited good size uniformity and regularity. The absorption edge of ZnFe2O4 nanospheres shifted to a higher energy in the UV–Vis absorption spectrum compared with that of ZnFe2O4 nanoparticles. The ZnFe2O4 nanospheres exhibited remarkably high surface photovoltage response in the UV and visible region, suggesting the enhanced separation ability of photogenerated electrons and holes. The dramatically enhanced photocatalytic activity of the ZnFe2O4 nanospheres was evaluated in the decomposition of rhodamine B under Xe lamp irradiation. Hydroxyl radicals on the surface of photoilluminated ZnFe2O4 nanospheres were detected by the photoluminescence technique, which suggested that hydroxyl radicals played an important role in the photocatalytic reaction. This study provided new insight into the design and preparation of functional nanomaterials with sphere structure in high yield, and the as-grown architectures demonstrated an excellent ability to remove organic pollutants in wastewater.
Keywords: Sphere-like; Zinc ferrite; Template-free; Photocatalytic; Hydroxyl radicals;

Fluorescent hollow/rattle-type mesoporous Au@SiO2 nanocapsules for drug delivery and fluorescence imaging of cancer cells by Ting-Ting Wang; Fang Chai; Chun-Gang Wang; Lu Li; Hai-Yan Liu; Ling-Yu Zhang; Zhong-Min Su; Yi Liao (109-115).
Multifunctional uniform and versatile hollow and rattle-type nanocapsules composed of spindle-shaped Au nanoparticles as cores and fluorescent mesoporous silica shells with tunable optical and fluorescent properties have been developed by controlled etching Au nanorods coated with mesoporous SiO2 in a facile way. The combined functionalities of simultaneous cell imaging and drug delivery of the synthesized nanocapsules have also been demonstrated..Display Omitted► Multifunctional uniform and versatile hollow and rattle-type mesoporous silica nanocapsules were fabricated in a facile way. ► The obtained multifunctional rattle-type mesoporous silica nanocapsules have tunable optical and fluorescent properties. ► The fluorescent rattle-type nanocapsules with Au nanoparticles were used for drug delivery and fluorescence imaging for cancer cells.Multifunctional uniform and versatile hollow and rattle-type nanocapsules composed of spindle-shaped Au nanoparticles as cores and fluorescent mesoporous silica shells with tunable optical and fluorescent properties have been developed by controlled etching Au nanorods (AuNRs) coated with mesoporous SiO2 (AuNR@mSiO2) via a small amount of aqua regia (volume ratio HCl/HNO3  = 3/1) as an etching agent in a facile way. The etching process can be tracked by UV–Vis absorption and fluorescence spectroscopy and the size of cavities in the hollow/rattle-type particles can be tuned by controlling the reaction time. The dye molecules incorporated in mSiO2 walls enabled the nanocapsules to be utilized as a fluorescent imaging agent in cancer cell imaging. Furthermore, such hollow/rattle-structured nanocapsules have the merit of enhanced drug loading capacity acting as carriers for the loading and delivery of an anticancer drug, doxorubicin hydrochloride (DOX), with higher storage for cancer therapy. Herein, the combined functionalities of simultaneous cell imaging and drug delivery of the synthesized nanocapsules have been demonstrated, which provide a very promising candidate for application in optical imaging and drug delivery for cancer cells.
Keywords: Mesoporous silica nanocapsule; Gold nanoparticles; Controlled etching; Drug release; Fluorescent imaging;

Microwave irradiated click reactions on silicon surfaces via derivertization of covalently grafted poly(PEGMA) brushes by Xiang Liu; Hong-Ning Zheng; Yin-Zhou Ma; Qing Yan; Shou-Jun Xiao (116-122).
Poly(poly(ethylene glycol) monomethacrylate) brushes grafted from a planar silicon hydride surface were converted to azide-/acetylene-terminated brushes. Then surface click reactions were executed by microwave irradiation under extremely mild conditions.Display Omitted► Click reactions were executed on polymer brushes via silicon surface induced ATRP. ► Microwave irradiation assisted surface click reactions at 30 °C for 1 h. ► MTR-IR Spectroscopy reveals tiny details of click reactions. ► Microwave-assisted surface reactions could have broad application.Two surface chemistry approaches were realized to complete click reactions at covalently grafted polymer brushes of poly(poly(ethylene glycol) monomethacrylate) on a planar silicon surface (Si-g-P(PEGMA―OH)). On one hand, the hydroxyls from Si-g-P(PEGMA―OH) brushes can be replaced by chlorines of thionyl chloride and then chlorines can be substituted with azides of sodium azide to achieve azide-terminated (Si-g-P(PEGMA―N3)) brushes. On the other hand, the terminal acetylene (Si-g-P(PEGMA―CH2CCH)) brushes can be prepared easily by reaction between Si-g-P(PEGMA―OH) and propargyl bromide. Model compounds of acetylene-terminated propargylamine, propiolic acid, and 10-undecynoic acid as well as azide-terminal benzyl azide were chosen to investigate the surface click reactions catalyzed with Cu(II)/sodium L-ascorbate by microwave irradiation under very mild conditions at 30 °C for 1 h. The stepwise modifications were characterized by two surface-sensitive techniques, Multiple Transmission-Reflection Infrared Spectroscopy (MTR-IR) and X-ray Photoelectron Spectroscopy (XPS), and their spectra were analyzed in detail. The triazole ring v(H―C=) stretching at 3139 cm−1 and the XPS high-resolution scan of N 1s directly confirm the click reactions. By quantifying their infrared spectra before and after click reactions, we conclude that the click reactions on silicon surfaces by microwave irradiation possess high yield and efficiency. Hence, the microwave irradiated click reaction approaches might open convenient avenues to fabricate functional and hybrid organic/silicon devices.
Keywords: Planar silicon surface; Polymer brushes; Poly(poly(ethylene glycol) monomethacrylate); Click chemistry; Microwave irradiation;

Electrophoretic mobility of poly(acrylic acid)-coated alumina particles by Prasad S. Bhosale; Jaehun Chun; John C. Berg (123-128).
Change in electrophoretic mobility of poly(acrylic acid)-coated and bare alumina particles with electrolyte concentration.Display Omitted► Dynamic and steady state (dc) electrophoretic mobility of PAA coated colloidal alumina. ► Variables: PAA molecular weight (MW) and concentration; salt concentration and type. ► All but lowest MW reduces dynamic electrophoretic mobility due to bridging. ► Same enhancement in surface charge independent of PAA MW. ► Bridging influenced by cation type (Na+, K+, Cs+) at high ionic strengths.The effect of poly (acrylic acid) (PAA) adsorption on the electrokinetic behavior of alumina dispersions under high pH conditions was investigated as a function of polymer concentration and molecular weight as well as the presence, concentration and ion type of background electrolyte. Systems of this type are relevant to nuclear waste treatment, in which PAA is known to be an effective rheology modifier. The presence of all but the lowest molecular weight PAA studied (1800) led to decreases in dynamic electrophoretic mobility at low polymer concentrations, attributable to bridging flocculation, as verified by measurements of particle size distribution. Bridging effects increased with polymer molecular weight, and decreased with polymer concentration. Increases in background electrolyte concentration enhanced dynamic electrophoretic mobility as the polymer layers were compressed and bridging was reduced. Such enhancements were reduced as the cation was changed from K+ to Na+ to Cs+.
Keywords: Poly (acrylic acid); Electrophoretic mobility; Acoustic electrophoresis; Nuclear waste simulant;

Extent and mechanism of metal ion incorporation into precipitated ferrites by Sivan Klas; Yael Dubowski; Gumelar Pritosiwi; Joachim Gerth; Wolfgang Calmano; Ori Lahav (129-135).
The incorporation extent of a dissolved metal ion into a precipitated ferrite seems to relate predominately to the water exchange rate between its surrounding hydration shells.Display Omitted► Zn and Co can be fully incorporated. Ni, Al, and Cd incorporation is limited. ► Cr does not enter the ferrite structure. ► Cr and Ni form amorphous solid phases resistant to dissolution at pH 2.0. ► The incorporation extent is affected predominantly by the water exchange rate.The ability of many noniron metals to be incorporated into the structure of ferrites is being utilized in numerous industrial and environmental applications. The incorporation of some of these metals during Fe(II) oxidation-induced precipitation at moderate temperatures (80–100 °C) appears to be limited, for reasons not fully understood, and to extents not always agreed (e.g., Ni2+, Cr3+). In this paper, the incorporation maxima of six metals into the structure of precipitated ferrites (in terms of x in Me x Fe3− x O4, Me represents a noniron metal) were concluded to be 1.0, 1.0, 0.78, 0.49, 0.35, and 0.0 for Zn2+, Co2+, Ni2+, Al3+, Cd2+ and Cr3+, respectively. With the exception of the much larger Cd2+, these values were associated with kinetic considerations controlled by the H2O exchange rate between the hydration shells surrounding the dissolved metal ion.
Keywords: Ferrite; Ion incorporation; Isomorphous substitution; Coprecipitation; Substituted magnetite;

Fl–DFO molecules@mesoporous silica materials: Highly sensitive and selective nanosensor for dosing with iron ions by Bao-Lian Su; Nicolas Moniotte; Noan Nivarlet; Li-Hua Chen; Zheng-Yi Fu; Jonathan Desmet; Jing Li (136-145).
Highly sensitive and selective nanosensor for labil iron pool (LIP) determination has been designed and prepared by immobilization of Fluoresceine–Desferrioxamine (Fl–DFO) into highly ordered mesoporous silica.Display Omitted► Highly selective and sensitive nanosensor. ► Fl–DFO/highly ordered mesoporous silica. ► Fl–DFO surface anchoring by covalent binding. ► Fl–DFO molecule location on the fluorescence properties. ► Iron ions dosing.Highly sensitive and selective nanosensor for labile iron pool (LIP) determination, has been designed and prepared by immobilization of Fluoresceine–Desferrioxamine (Fl–DFO), a bifunctional fluoro-siderophore probe molecule with great affinity for iron ions (pKf  = 30.7), into highly ordered mesoporous silica structure. Different immobilization methods of Fl–DFO molecules, such as their encapsulation in surfactant micelles used as templating agents for the synthesis of mesoporous silica, direct impregnation into the mesochannels of as-synthesized mesoporous silica and their surface anchoring by covalent binding with propylamine groups implanted by post-synthesis on the internal surface of mesochannels, have been explored. Each nanohybrid has been fully characterized by small angle XRD, TEM, SEM, solid state 29Si and 13C MAS NMR and N2 adsorption–desorption. The fluorescence properties of nanohybrids obtained have been correlated with the immobilization methods, generating interesting information concerning the localization of Fl–DFO molecules in the channels of mesoporous silica. The leaching of Fl–DFO molecules from mesoporous materials has been investigated. The nanosensor prepared by surface anchoring of Fl–DFO at the internal surface of mesochannels showed high performances with no leaching effect and high sensitivity in regards to its responses to ferric ions. Its fluorescence intensity decreased as soon as first FeIII ions are in contact with this nanosensor. A linear relationship between the fluorescence intensity and the ferric ions concentration was observed in low micromolar range. The selectivity of this nanosensor towards other metal ions has also been tested and shown its high affinity to ferric ions. This study can allow the design of a stable, portable, simple, regenerable and cost-effective nanosensor highly sensitive and selective for iron ions with detection limits in the range of cellular LIP in cells, e.g. lower micromolar range.
Keywords: Fluoresceine–Desferrioxamine (Fl–DFO); Sensor molecule; Mesoporous silica; Nanosensor; Dosing with iron ions;

Carbon nanoparticle ionic liquid hybrids and their photoluminescence properties by Ying Wei; Yang Liu; Haitao Li; Xiaodie He; Qingguo Zhang; Zhenhui Kang; Shuit-Tong Lee (146-150).
Carbon nanoparticle ionic liquid hybrids with strong photoluminescence and high conductivity.Display Omitted► Fluorescent CNPIL hybrids were synthesized by a microwave synthetic method. ► The CNPIL hybrids exhibit colorful PL covering the entire visible–NIR range. ► The CNPIL hybrids possess up conversion PL properties and high conductivity. ► The PL of CNPIL hybrids are pH dependent and can be controlled by water content.A fluorescent carbon nanoparticle ionic liquid hybrids (CNPIL) with high conductivity is synthesized by a facile one-step microwave method from ionic liquid 1-butyl-3-methylimidazolium glutamine salt and Glucose. This CNPIL exhibits excellent PL properties: bright and colorful PL covering the entire visible–NIR spectral range, up conversion PL properties, pH dependent and can be controlled by the reaction condition.
Keywords: Carbon nanoparticles; Ionic liquid; Hybrid; Photoluminescence;

Addition of 1,2-ethanedithiol to dispersions of PbS nanocrystals triggers aggregation of tunable QD assemblies that can be trapped in polymer films by spin casting.Display Omitted► PbS dispersion aggregation is controlled by fractional coverage by ethanedithiol. ► Extended QD networks can be prepared if fractional coverage is less than 1.0. ► Micrometre-sized crystals form if fractional coverage is greater than 1.0. ► Triggered aggregation in dispersion may enable morphology control in hybrid polymer films.Hybrid polymer films consist of quantum dots (QDs) dispersed in a polymer matrix. A key fundamental challenge that is hindering their optimisation in optoelectronic devices such as hybrid solar cells is overcoming uncontrolled aggregation of the QDs. In an effort to direct aggregation, and trigger self-assembly, we added a bilinker ligand (1,2-ethanedithiol) to dispersed PbS QDs in polymer solutions prior to film deposition by spin casting. Turbidity studies of the PbS QD/1,2-ethanedithiol dispersions enabled a relationship to be established between the extent of 1,2-ethanedithiol-triggered QD aggregation and the nominal fractional coverage of the QDs by 1,2-ethanedithiol. The extent of aggregation (and self-assembly) increased with nominal fraction coverage. Above a value of about 1.0 QD aggregation increased substantially. TEM images showed that at low 1,2-ethanedithiol concentrations triggered assembly of network-like QD structures occurred. At high 1,2-ethanedithiol concentrations the QDs self-assembled into more-ordered micrometre-sized crystals. The results suggest that 1,2-ethanedithiol decreases the inter-QD separation in dispersion as a result of rapid ligand exchange and this process results in QD aggregation as well as self-assembly. The assembled QD structures were successfully trapped within polymer films by spin casting of PbS QD/1,2-ethanedithiol dispersions containing added polystyrene or polytriarylamine.
Keywords: Triggered aggregation; PbS; Quantum dots; Hybrid polymer films;

Effect of head group size, temperature and counterion specificity on cationic micelles by Alessandro Di Michele; Lucia Brinchi; Pietro Di Profio; Raimondo Germani; Gianfranco Savelli; Giuseppe Onori (160-166).
Specific conductivity vs mole fraction of CTACl at different temperature.Display Omitted► In this study, we have reported experimental results concerning the temperature variations of the cmc of four cationic micelles differing in head group size and counterion type. ► The conductance plots for cmc determinations were used to estimate the extent of counterion binding to the micelle. ► The micelle ionization degree increases with the size of the ionic head group and with the size of the counterion. ► Thermodynamic analysis of micelle formation has often been made only from cmc change with temperature and using a polynomial-function description of this dependence.The critical micelle concentration (cmc) and ionisation degree (α), of micelles of cetyltrimethylammonium bromide (CTABr), cetyltrimethylammonium chloride (CTACl), cetyltripropylammonium bromide (CTPABr) and cetyltripropylammonium chloride (CTPACl) have been measured over a narrow temperature range at 2 degree intervals using electrical conductivity. CTPACl and CTPABr are very soluble in water and were measured in the temperature range 275.15–323.15 K. The Krafft temperatures for CTABr and for CTACl are 293.15 K and 284.15 K, respectively and established a lower temperature limit for our studies on these two surfactants. The cmc vs temperature curves have a smooth minimum near room temperature and α linearly increases with temperature. The changes of cmc and α with temperature are smaller than those associated with the modification of head group size or counterion nature. Using these results, basic thermodynamic quantities associated with the phenomena of micellization have been evaluated. Thermodynamic properties of the surfactant solutions were discussed in terms of temperature dependence of the free energy, enthalpy and entropy of micellization. A close similarity between the effects of change in temperature on protein folding and micellization process appears from the data.
Keywords: Micellization; Ionisation degree; Critical micelle concentration; Enthalpy; Entropy;

CD spectra show three different sequences of thrombospondin-1 (TSP-1B), but interactions do not result in a noticeable conformational change except for TSPB-(Abu)6 due to its cyclic aspartamide. CD spectra of peptides [A] TSP-B, [B] TSP-B(E), [C] TSP-B(S), and [D] TSP-B(Abu)6 in TFE/PBS mixtures (1/1). Peptide concentration 50 μM.Display Omitted► We study the reasons for differences in activity found between 4 thrombospondin-related peptides. ► Peptide with an imide cyclic group was the only one active biologically. ► Its CD spectrum was strongly affected by the presence of trifluoroethanol. ► The presence of DPPC induced a soft conformational change in the same peptide. ► Other techniques were used for this purpose and the results obtained were not relevant.Thrombospondin-1 (TSP-1) is a protein involved in angiogenesis and tumor metastasis. In a previous study, a tridecapeptide sequence of TSP-1B [KRFKQDGGWSHWG] was synthesized and its biological activity was determined as well as the activity of three related sequences TSPB-(E), TSPB-(S), and TSPB-(Abu)6. These peptides were tested for activity on the cell growth of three human carcinoma cells lines and only TSPB-(Abu)6 increased proliferation of MCF7 and HT-29. The main aim of this study was to perform physicochemical measurements, in a comparative way, to determine if the differences in activity could be related to physicochemical properties. Peptides were characterised by HPLC capacity factors, UV, fluorescence, and CD spectra (either in buffer solution or in the presence of lipid vesicles), surface activity, and aggregation. Moreover, the interaction of these peptides with phospholipids was determined through their penetration in monolayers of DPPC, PG, or PS as well as their miscibility in mixed monolayers. Besides, using liposomes as model membranes, the affinity of these peptides for phosphatidylcholine was measured with vesicles labeled with fluorescent markers (TMA-DPH, laurdan, pyrene). Results show that these molecules are highly hydrophilic and their surface activity is low. Mixed monolayers indicate that there is almost no miscibility. Besides, its presence does not modify noticeably the microviscosity of bilayers. Moreover, UV and fluorescence spectra of peptides were not affected by the presence of lipids in the media but CD spectra recorded in TFE/water (1/1) resulted in small changes for TSPB, TSPB-(E), and TSPB-(S) peptides. On the contrary CD spectra of TSPB-(Abu)6 derivatives were clearly much more sensitive to the polarity of the environment. According to these data the biological activity of peptide with a cyclic aspartimide moiety at position 6 could be related to a specific conformational change in the peptide chain promoted by a hydrophobic membrane-like environment.
Keywords: Peptide synthesis; Monomolecular layers; Thrombospondin; Fluorescence; Surface activity; Phospholipids; Circular dichroism;

Molecular dynamics simulations of inverse sodium dodecyl sulfate (SDS) micelles in a mixed toluene/pentanol solvent in the absence and presence of poly(diallyldimethylammonium chloride) (PDADMAC) by Armen H. Poghosyan; Levon H. Arsenyan; Hrant H. Gharabekyan; Sandra Falkenhagen; Joachim Koetz; Aram A. Shahinyan (175-181).
An aqueous SDS-micelle dissolved in a toluene/pentanol mixture in the presence of a cationic polyelectrolyte has been examined using MD simulations.Display Omitted► We have done a molecular dynamics simulation of a complex system in toluene/pentanol solvent. ► The main structural and dynamical properties have been examined. ► The computer simulation study is in full agreement with experimental data.We have performed a 15 ns molecular dynamics simulation of inverse sodium dodecyl sulfate (SDS) micelles in a mixed toluene/pentanol solvent in the absence and presence of a cationic polyelectrolyte, i.e. poly(diallyldimethylammonium chloride) (PDADMAC). The NAMD code and CHARMM force field were used. During the simulation time, the radii of SDS inverse micelles changed and the radii of the water droplets have been calculated. The behavior of SDS hydrocarbon chains has been characterized by calculating the orientation order parameter and the chain average length. The water droplet properties (water flow, water molecules displacement) have been examined. In summary the MD simulations indicate a more rigid and ordered surfactant film due to the formation of a polyelectrolyte palisade layer in full agreement with the experimental findings, e.g. the viscosity increase and shift of the percolation boundary.
Keywords: Surfactant micelles; Molecular dynamics simulations; SDS;

An alkyl polyglucoside-mixed emulsifier as stabilizer of emulsion systems: The influence of colloidal structure on emulsions skin hydration potential by Snezana Savic; Milica Lukic; Ivana Jaksic; Stephan Reichl; Slobodanka Tamburic; Christel Müller-Goymann (182-191).
The complex lamellar mesophase in C12/14 APG-mixed emulsifier-stabilized binary and emulsion systems (without and with glycerol)—a depiction of TEM micrographs.Display Omitted► C12/14 alkyl polyglucoside surfactant studied in glycerol-containing gel emulsions. ► It creates the complex lamellar mesophase in the concentration range 10–25%. ► By 15% of emulsifier, oil and glycerol produce the largest interlamellar space. ► Such colloidal structure results in the most effective skin hydration.To be considered as a suitable vehicle for drugs/cosmetic actives, an emulsion system should have a number of desirable properties mainly dependent on surfactant used for its stabilization. In the current study, C12–14 alkyl polyglucoside (APG)-mixed emulsifier of natural origin has been investigated in a series of binary (emulsifier concentration 10–25% (w/w)) and ternary systems with fixed emulsifier content (15% (w/w)) with or without glycerol. To elucidate the systems’ colloidal structure the following physicochemical techniques were employed: polarization and transmission electron microscopy, X-ray diffraction (WAXD and SAXD), thermal analysis (DSC and TGA), complex rheological, pH, and conductivity measurements. Additionally, the emulsion vehicles’ skin hydration potential was tested in vivo, on human skin under occlusion. In a series of binary systems with fixed emulsifier/water ratios ranging from 10/90 to 25/75 the predominance of a lamellar mesophase was found, changing its character from a liquid crystalline to a gel crystalline type. The same was observed in gel emulsions containing equal amounts of emulsifier and oil (15% (w/w)), but varying in glycerol content (0–25%). Different emulsion samples exhibited different water distribution modes in the structure, reflecting their rheological behavior and also their skin hydration capacity.
Keywords: Alkyl polyglucoside-mixed emulsifier; Lamellar mesophase; Water distribution; Rheological behavior; Skin hydration;

Molecular aspects of the interaction between plants sterols and DPPC bilayers by Claudia Silva; Francisco J. Aranda; Antonio Ortiz; Vicente Martínez; Micaela Carvajal; José A. Teruel (192-201).
Molecular conformers of DPPC predicted in the presence of plant sterols. In gray it is shown the tilting effect caused in a DPPC molecule by the inclusion of sitosterol or stigmasterol in a DPPC membrane.Display Omitted► We have studied the differential effects between sitosterol and stigmasterol on a DPPC membrane. ► Sitosterol results to be more efficient in ordering a fluid DPPC membrane than stigmasterol. ► Molecular dynamics studies are carried out to understand the effect of both sterols. ► A molecular model is proposed to explain sterol-DPPC interactions and membrane structure.The effect of sterols composition in a lipid bilayer was investigated on membranes of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and mixtures with the plant sterols β-sitosterol and stigmasterol. Differential scanning calorimetry, 1,6-diphenyl-1,3,5-hexatriene (DPH) fluorescence polarization and infrared spectroscopy studies showed that both sterols changed the packing of the membrane and the hydration of the polar headgroup of the phospholipids, disordering the gel phase and, vice versa, ordering the membrane in the liquid crystalline phase. In all cases some differences among β-sitosterol and stigmasterol could be observed, being β-sitosterol slightly more efficient than stigmasterol in ordering a fluid membrane, bringing the membrane to a more packed liquid ordered phase. Molecular dynamic simulations were carried out to better characterize the distinct behavior of both sterols in a DPPC-membrane. The calculated parameters agreed quite well with the experimental results and a molecular model is proposed to explain differences in the sterols molecules and their effect on the DPPC-bilayer.
Keywords: Lipid composition; Lipid membrane; DPPC; Sterols; Sitosterol; Stigmasterol; Molecular dynamics;

QSPR modeling of nonionic surfactant cloud points: An update by Yueying Ren; Baowei Zhao; Qing Chang; Xiaojun Yao (202-207).
The support vector machine (SVM) model is tested in the current study. The use of this SVM approach to predict properties of unknown surfactants has been checked with an independent external test set of 16 compounds. This figure shows a good correlation between predicted and reported cloud-point values.Display Omitted► Support vector machine was used to investigate the cloud points of surfactants. ► Molecular structures were examined using principal component analysis. ► The optimum model was checked using an external set of 16 different compounds. ► Properties of 14 out of 16 external surfactants were predicted very well.Quantitative structure–property relationship (QSPR) models for the cloud points of nonionic surfactants were developed based on CODESSA descriptors. Essentials accounting for a reliable model were considered carefully. Four descriptors were selected by a generic algorithm (GA) method to link the structures of nonionic surfactants to their corresponding cloud-point values. The descriptors were also analyzed using principal component analysis (PCA). Nonlinear models based on support vector machine (SVM) and projection pursuit regression (PPR) were also developed. All models were validated in two ways, i.e., internal cross-validation (CV) and a test set. The results are discussed in light of the main factors that influence the property under investigation and its modeling. In addition, an independent external data set of 16 nonionic surfactants was used to check the generalization ability of the optimum model.
Keywords: QSPR; Nonionic surfactant; Cloud point; Principal component analysis; Support vector machine; Projection pursuit regression;

Interactions of sodium N-lauroylsarcosinate with N-alkylpyridinium chloride surfactants in their aqueous mixtures results in spontaneous formation of pH sensitive stable unilamellar vesicles.Display Omitted► Interaction of a carboxylate surfactant with two cationic surfactants was studied. ► Spontaneous formation of stable catanionic vesicles has been demonstrated. ► Vesicles are spherical and are stable upon ageing for a long period of time. ► The vesicles were shown to be pH-sensitive. ► pH-triggered release of model drug has been demonstrated.The interaction of sodium N-lauroylsarcosinate (SLS) with N-cetylpyridinium chloride (CPC) and N-dodecylpyridinium chloride (DPC) was investigated in aqueous mixtures. A strong interaction between the anionic and cationic surfactants was observed. The interaction parameter, β was determined for a wide composition range and was found to be negative. The mixed systems were found to have much lower critical micelle concentration (cmc) and surface tension at cmc. The surfactant mixtures exhibit synergism in the range of molar fractions investigated. The self-assembly formation in the mixtures of different compositions and total concentrations were studied using a number of techniques, including surface tension, fluorescence spectroscopy, dynamic light scattering (DLS), transmission electron microscopy (TEM), confocal fluorescence microscopy (CFM). Thermodynamically stable unilamellar vesicles were observed to form upon mixing of the anionic and cationic surfactants in a wide range of composition and concentrations in buffered aqueous media. TEM as well as DLS measurements were performed to obtain shape and size of the vesicular structures, respectively. These unilamellar vesicles are stable for periods as long as 3 months and appear to be the equilibrium form of aggregation. Effect of pH, and temperature on the stability was investigated. The vesicular structures were observed to be stable at pH as low as 2.0 and at biological temperature (37 °C). In presence of 10 mol% of cholesterol the mixed surfactant vesicles exhibited leakage of the encapsulated calcein dye, showing potential application in pH-triggered drug release.
Keywords: Mixed surfactant; Synergism; Vesicles; Fluorescence; Microscopy; Light scattering;

Interactions of hydrophilic silica nanoparticles and classical surfactants at non-polar oil–water interface by Nasrin Ghouchi Eskandar; Spomenka Simovic; Clive A. Prestidge (217-225).
Freeze fracture-SEM of silica-coated oleylamine-stabilised liquid paraffin-in-water emulsions (inset image) showed scattered particle flocs at the droplet surface in line with low magnitude of the attachment energy (E<  500 kT) and poor physical stability.Display Omitted► This work aims to investigate synergistic stabilisation of paraffin oil-in-water emulsions using conventional surfactants and hydrophilic silica nanoparticles. ► The attachment energy of silica nanoparticles at the paraffin oil (dissolved lecithin)–water interface was calculated to be 900–4500 kT. ► The attachment energy of silica nanoparticles at the paraffin oil (dissolved oleylamine)–water interface was calculated to be 250–550 kT. ► Calculated attachment energies correlated well with the long-term emulsion stability, which is significantly higher for lecithin/silica stabilised emulsions.The interfacial and bulk properties of submicron oil-in-water emulsions simultaneously stabilised with a conventional surfactant (either lecithin or oleylamine) and hydrophilic silica nanoparticles (Aerosil®380) were investigated and compared with emulsions stabilised by either stabiliser. Emulsions solely stabilised with lecithin or oleylamine showed poor physical stability, i.e., sedimentation and the release of pure oil was observed within 3 months storage. The formation and long-term stability of silica nanoparticle-coated emulsions was investigated as a function of the surfactant type, charge, and concentration; the oil phase polarity (Miglyol®812 versus liquid paraffin); and loading phase of nanoparticles, either oil or water. Highly stable emulsions with long-term resistance to coalescence and creaming were formulated even at low lecithin concentrations in the presence of optimum levels of silica nanoparticles. The attachment energy of silica nanoparticles at the non-polar oil–water interface in the presence of lecithin was significantly higher compared to oleylamine in line with good long-term stability of the former compared to the sedimentation and release of oil in the latter. The attachment energy of silica nanoparticles at the polar oil–water interface especially in the presence of oleylamine was up to five-times higher compared to the non-polar liquid paraffin. The interfacial layer structure of nanoparticles (close-packed layer of particle aggregates or scattered particle flocs) directly related to the free energy of nanoparticle adsorption at both MCT oil and liquid paraffin–water interfaces.
Keywords: Pickering emulsions; Silica nanoparticles; Surfactans; Interfacial tension; Contact angle; Attachment energy;

Depletion interactions owing to non-interacting PSSNa assist the formation of dilute PEO aggregates, which break down upon adding simple screening salt.Display Omitted► PEO molecules form Gaussian chains in dilute aqueous solutions at ambient temperature. ► With added PSSNa depletion interactions assist the formation of dilute PEO aggregates. ► These dilute PEO aggregates break down upon adding simple screening salt.Dilute aqueous solutions of d-PEO and PSSNa mixtures were studied by 2H NMR spectroscopy and small-angle neutron scattering (SANS). The interactions between d-PEO and PSSNa were found to be negligible both in the presence and absence of NaCl. At very dilute concentration (0.7 mg mL−1), d-PEO chains were still found to be slightly collapsed at ambient temperature in water. Upon the addition of PSSNa, aggregates of d-PEO were observed with d-PEO coils loosely associated with each other. The average centre to centre distance between d-PEO coils, which was calculated from the maxima in SANS spectra, was similar to the size of the individual coils. The effect of a simple salt, NaCl, on d-PEO-PSSNa interaction was investigated. Salt addition induced a breakdown of the dilute d-PEO aggregates.
Keywords: PEO; PSSNa; SANS; Dilute aggregate; Aqueous solution;

Adsorptive removal of arsenic from water by an iron–zirconium binary oxide adsorbent by Zongming Ren; Gaosheng Zhang; J. Paul Chen (230-237).
Arsenate is removed by Fe–Zr binary oxide through formation of inner-sphere surface complexes, while As(III) is removed by formation of both inner- and outer-sphere surface complexes.Display Omitted► The Fe–Zr binary oxide has high adsorption capacity toward both As(V) and As(III). ► Co-existing anions did not significantly influence the arsenic adsorption. ► As(V) is adsorbed by formation of inner-sphere surface complexes. ► As(III) is adsorbed by formation of both inner- and outer-sphere surface complexes.Arsenate and arsenite may exist simultaneously in groundwater and have led to a greater risk to human health. In this study, an iron–zirconium (Fe–Zr) binary oxide adsorbent for both arsenate and arsenite removal was prepared by a coprecipitation method. The adsorbent was amorphous with a specific surface area of 339 m2/g. It was effective for both As(V) and As(III) removal; the maximum adsorption capacities were 46.1 and 120.0 mg/g at pH 7.0, respectively, much higher than for many reported adsorbents. Both As(V) and As(III) adsorption occurred rapidly and achieved equilibrium within 25 h, which were well fitted by the pseudo-second-order equation. Competitive anions hindered the sorption according to the sequence PO 4 3 - > SiO 3 2 - > CO 3 2 - > SO 4 2 - . The ionic strength effect experiment, measurement of zeta potential, and FTIR study indicate that As(V) forms inner-sphere surface complexes, while As(III) forms both inner- and outer-sphere surface complexes at the water/Fe–Zr binary oxide interface. The high uptake capability and good stability of the Fe–Zr binary oxide make it a potentially attractive adsorbent for the removal of both As(V) and As(III) from water.
Keywords: Fe–Zr binary oxide; Arsenate; Arsenite; Adsorption; Removal;

One-step in situ synthesis of NH x -adsorbed rhodium nanocrystals at liquid–liquid interfaces for possible electrocatalytic applications by V.S. Patil; S.R. Krishna; R.R. Hawaldar; A.B. Gaikwad; S.D. Sathaye; K.R. Patil (238-244).
Space confinement in LLIRT is a superior technique for depositing nanoparticulate materials in an ultrathin film form as shown for rhodium films in this paper.Display Omitted► One-step in situ synthesis of nanomaterial. ► In situ product of reaction can be conveniently used to arrest the growth of the particles by space confinement. ► This technique can be extended to obtain nanoparticulate thin films of other materials as well.Nearly monodisperse rhodium nanoparticles with adsorbed NH x were synthesized at the CCl4 water interface. The presence of NH x -adsorbed species was confirmed by energy-dispersive X-ray analysis (EDX) and X-ray photoelectron spectroscopy (XPS) studies. The synthesis of controlled size 2–38 nm rhodium particles was studied as a function of reducing agent concentration by transmission electron microscopy (TEM). HRTEM confirmed the formation of rhodium nanoparticles having fringe spacing consistent with reported Rh (1 1 1) planes. The continuity of these films over an area of 1 × 1 μm was revealed by atomic force microscopy (AFM) studies. The electrocatalytic application of these nanostructure Rh-NH x thin films for formaldehyde oxidation in 0.5 M NaOH was investigated by cyclic voltammetry. The Rh nanoparticles formed by the present strategy are expected to be useful for other catalytic applications also.
Keywords: Rhodium; Hydrazine hydrate; Nanoparticles; Liquidliquid interface; Thin films;

Adsorption-driven molecular recognitive photocatalytic decomposition of organic molecules in aqueous mixtures was achieved on TiO2/nanoporous silica core/shell particles with controlled pore diameters.Display Omitted► Nanoporous silica coating to impart molecular selective photocatalytic ability to TiO2 particle. ► P25 core/nanoporous silica shell particles with different size and silanol density of the pores. ► The hybrid materials exhibit molecular recognitive adsorption and photocatalysis.The coating of TiO2 particles (P25) by a nanoporous silica layer was conducted to impart molecular recognitive photocatalytic ability. TiO2/nanoporous silica core/shell particles with varied pore diameters of the shell were synthesized by the reaction of P25 with an aqueous mixture of tetraethoxysilane and alkyltrimethylammonium chloride with varied alkyl chain lengths, followed by calcination. The TEM and nitrogen adsorption/desorption isotherms of the products showed that a nanoporous silica shell with a thickness of ca. 2 nm and controlled pore diameter (1.2, 1.6, and 2.7 nm) was deposited on the titania particle when surfactants with different alkyl chain lengths (C12, C16 and C22) were used. The water vapor adsorption/desorption isotherms of the core/shell particles revealed that a larger amount of water adsorbed on the core/shell particles when the pore diameter is larger. The 29Si MAS NMR spectra of the core/shell particles showed that the amount of surface silanol groups was independent of the water vapor adsorption capacity of the products. The possible molecular recognitive photocatalysis on the products was investigated under UV irradiation using two kinds of aqueous mixtures containing different organic compounds with varied sizes and functional groups: a 4-butylphenol, 4-hexylphenol, and 4-nonylphenol mixture and a 2-nitrophenol, 2-nitro-4-phenylphenol, and 4-nitro-2,6-diphenylphenol mixture. It was found that the core/shell particles exhibited selective adsorption-driven molecular recognitive photocatalytic decomposition of 4-nonylphenol and 2-nitrophenol in the two mixtures.
Keywords: Photocatalysis; Molecular recognition; Mesoporous silica; Titania; Nonylphenol;

Synthesis of high-silica EU-1 zeolite in the presence of hexamethonium ions: A seeded approach for inhibiting ZSM-48 by Qinghu Xu; Yanjun Gong; Wenjing Xu; Jun Xu; Feng Deng; Tao Dou (252-260).
By seeded approach, pure EU-1 with SiO2/Al2O3  > 240 were synthesized in HM system and the co-crystalline of ZSM-48/EU-1 or pure ZSM-48 was also tunable.Display Omitted► A seeded approach to synthesize of very high-silica EU-1 in HM system. ► Control of high- silica EU-1, co-crystalline of ZSM-48/EU-1 and ZSM-48. ► Role of seeds to reduce the Ea of EU-1 nucleation and inhibit ZSM-48 phase. ► HM and Al from seeds performed synergy in the crystallization of silica-rich gels.A seeded approach was developed to synthesize high-silica EU-1 zeolite via inhibiting the co-crystallization of ZSM-48 in the presence of hexamethonium (HM) ions. A systematic study was carried out to determine factors such as seed content and SiO2/Al2O3 ratio, which influenced the crystallization of high-silica EU-1 and transformation of EU-1 into ZSM-48. Using EU-1 seeds, not only well-crystallized pure EU-1 zeolites with SiO2/Al2O3 ratios more than 500 were synthesized, but also the co-crystalline of ZSM-48/EU-1 or pure ZSM-48 was obtained in control from silica-rich mixture gels. Furthermore, the kinetic features of the seeded synthesis of EU-1 zeolites with SiO2/Al2O3 ratios of 55, 190, and 500 were examined. It was found that seeds played crucial roles in the decrease of apparent activation energy of EU-1 nucleation and inhibiting the transformation of EU-1 into ZSM-48. The HM and Al species performed synergistic roles to inhibit the formation ZSM-48 during high-silica EU-1 nucleation and crystal growth.
Keywords: High-silica EU-1; Seeded synthesis; Hexamethonium bromide; ZSM-48;

Heavy metals adsorption by novel EDTA-modified chitosan–silica hybrid materials by Eveliina Repo; Jolanta K. Warchoł; Amit Bhatnagar; Mika Sillanpää (261-267).
Novel porous EDTA-modified chitosan–silica hybrid materials were effective adsorbents for Co(II), Ni(II), Cd(II), and Pb(II).Display Omitted► Novel hybrid adsorbents combined beneficial properties of silica gel and chitosan. ► EDTA-modified hybrid materials were effective adsorbents for heavy metals. ► Porosity of the hybrid adsorbents affected the kinetics of the metal adsorption. ► Adsorption isotherms depended on the type of metal. ► Pb(II) had the highest adsorption efficiency from the mixed metal solutions.Novel adsorbents were synthesized by functionalizing chitosan–silica hybrid materials with (ethylenediaminetetraacetic acid) EDTA ligands. The synthesized adsorbents were found to combine the advantages of both silica gel (high surface area, porosity, rigid structure) and chitosan (surface functionality). The Adsorption potential of hybrid materials was investigated using Co(II), Ni(II), Cd(II), and Pb(II) as target metals by varying experimental conditions such as pH, contact time, and initial metal concentration. The kinetic results revealed that the pore diffusion process played a key role in adsorption kinetics, which might be attributed to the porous structure of synthesized adsorbents. The obtained maximum adsorption capacities of the hybrid materials for the metal ions ranged from 0.25 to 0.63 mmol/g under the studied experimental conditions. The adsorbent with the highest chitosan content showed the best adsorption efficiency. Bi-Langmuir and Sips isotherm model fitting to experimental data suggested the surface heterogeneity of the prepared adsorbents. In multimetal solutions, the hybrid adsorbents showed the highest affinity toward Pb(II).
Keywords: EDTA; Chitosan; Silica gel; Hybrid adsorbents; Adsorption; Heavy metals removal;

Synthesis and characterization of nanostructural polymer–silica composite: Positron annihilation lifetime spectroscopy study by Radosław Zaleski; Agnieszka Kierys; Marta Grochowicz; Marek Dziadosz; Jacek Goworek (268-276).
SEM micrograph of poly(TRIM)–Si composite bead after swelling in TEOS followed by its condensation.Display Omitted► Polymer–silica composite by swelling in TEOS. ► Calcination of composite gives the silica particles of spherical morphology porosity investigations by positron annihilation lifetime spectroscopy. ► Adsorption method and positronium annihilation lifetime spectroscopy (PALS) are compared.The swelling of poly(TRIM) spherical particles in TEOS is assessed as a potential way for obtaining polymer–silica nanocomposite materials. Silica deposition was achieved by simply stirring of swollen polymer particles in acidic hydrochloric-water solution. This procedure leads to spherical composite particles with dispersed silica gel within the polymer matrix. The resulting material exhibits the same morphology as the initial polymer. Nanocomposite particles are silica rich (about 17 wt.%). Characterization of the nanocomposites was performed using scanning electron microscopy, FT-IR spectroscopy, 29Si CP MAS NMR spectroscopy and thermogravimetry. Moreover, the use of positron annihilation lifetime spectroscopy PALS to characterize the structural properties of the nanocomposites is presented. This technique gave more realistic pieces of information about the pore structure of the investigated samples in contrast to nitrogen adsorption studies.
Keywords: Polymer–silica composite; Positron annihilation lifetime spectroscopy (PALS); Poly(TRIM); TEOS; Porosity;

Fabrication of superhydrophobic surface by hierarchical growth of lotus-leaf-like boehmite on aluminum foil by Lijun Liu; Jiashou Zhao; Yi Zhang; Fan Zhao; Yanbo Zhang (277-283).
The superhydrophobic and non-sticking surface with dual scale roughness has been fabricated by means of heterogeneous growth of lotus-leaf-like boehmite on aluminum foil for the first time.Display Omitted► Lotus-leaf-like boehmite was fabricated on the Al surface for the first time. ► The surface possesses dual scale roughness (nanoneedles on the microprotrusions). ► The surface exhibits superhydrophobic and non-sticking behaviors. ► The dual scale roughness accounts for the excellent superhydrophobicity.Hierarchical growth of boehmite film on the aluminum foil was carried out via a facile solution-phase synthesis route. The resultant film is composed of three-dimensional microprotrusions assembled from well aligned nanoneedles. Such dual scale micro-/nanostructures are highly similar with those of lotus leaves. The resultant surface after hydrophobization exhibits a water contact angle of 169° and a sliding angle of ∼4° for a 5 μL droplet, which is ascribed to the combination of the dual scale roughness at the micro- and nanometer scale and the low surface energy of stearic acid coating. The obtained film possesses relatively good adhesion to the aluminum substrate and keeps superhydrophobicity after the ultrasonic treatment or long-term storage in spite of the partial loss of it superhydrophobic ability after abrasion test.
Keywords: Dual scale roughness; Lotus effect; Aluminum; Boehmite; Hydrophobicity; Non-sticking behavior;

Spreading of a fluid phase on a spherical surface by Sui Tao; Wang Jiadao; Chen Darong (284-289).
This figure depicts the spreading of a fluid phase on a spherical surface with the increase of the fluid. When the three-phase contact line arrives at the limiting position, radius of the spherical fluid phase is infinite..Display Omitted► The contact angle of a fluid phase on a spherical surface is equal to Young contact angle. ► The three-phase contact line will approach a limit position with the spreading. ► A micro particle always “floats” on a fluid plane if its Young contact angle is not zero.The adsorption between a liquid drop and a micro-particle in an air or an air bubble and a micro-particle in water is dominated by liquid–solid or air–solid interfacial tension and wetting area of the liquid or air on the particle surface. The wetting area is determined by the spreading of the liquid drop or the bubble on the micro-particle. To explore this spreading, a wetting model of a fluid phase on a spherical particle was built. According to the theoretical results, the contact angle is constant when a fluid phase spreads on a spherical solid surface; the micro-particle can not submerge under a fluid when only interfacial tensions are involved and the wetting is not a complete wetting. The corresponding experiments were performed to confirm the theoretical results.
Keywords: Wetting; Superhydrophobic; Contact angle;

Solid pressure exists within the CP layer of colloids during ultrafiltration, where long-range interactions reduce the particle motion rate. Mass balance is used to quantify the development of CP layer.Display Omitted► Solid pressure exists in the concentration polarization layer of colloids. ► Solid and osmotic pressures are obtained separately. ► Interfacial interactions level off extent of concentration polarization. ► Ultrafiltration behaviors of colloidal particles are quantified.Here we describe the nature and implications of the “concentration polarization” (CP) layer that is formed during ultrafiltration of colloidal particles using a new approach in which the solid pressure, which arises from inter-particle interactions, and the inherent osmotic pressure are separately considered. The approach makes use of the particle transport mass balance between the convective and diffusive fluxes. The particle convection rate is hindered when inter-particle interactions take effect by reducing the particle velocities while the particle diffusion is solely controlled by the Brownian motion. An increase in solid pressure accounts for the reduction of the water potential caused by the relative motions of the particles and the surrounding water. A cell model is adopted to relate the local solid pressure with the local solid fraction and inter-particle interactions. The inter-particle interactions critically determine the form of particle accumulation (i.e. CP or gel/cake) on the membrane. The Shirato–Darcy equation is employed to relate the rate of increase in solid pressure, the relative liquid velocity and the solid fraction. Numerical integration approaches are employed to quantify the properties of the CP layer during both the development as well as the steady state phases (with steady state normally being achieved in a few minutes). The solid fractions are always no higher than those obtained when the inter-particle interactions are not considered. The decrease of the water potential caused by CP formation leads to the increase of both the solid pressure and the osmotic pressure. The dependence of the solid pressure on the solid fraction is usually stronger than that of the osmotic pressure. It is thus apparent that the solid pressure would be expected to dominate water potential reduction for solid fractions above a certain value though the solid pressure will be negligible when the solid fraction is relatively low.
Keywords: Concentration polarization; Particles; Membrane fouling; Solid pressure; Ultrafiltration; XDLVO;

Interfacial profiles in fluid/liquid systems: A description based on the storing of elastic energy by Aly J. Castellanos-Suárez; Jhoan Toro-Mendoza; Máximo García-Sucre (301-306).
Fluid/liquid interface schematic representation: (a) Two sub-phases are formed adjacent to the contact plane by the effect of the surface scalar potential φ and (b) in response to this potential each i-subphase has a proper stored energy density Ui (z) (▪ Similar fluids, ▪ different fluids).Display Omitted► An analytical expression for the elastic interfacial energy is proposed. ► The interfacial phenomena are considered as a response of a liquid in contact with other fluid phase. ► This model describes the molar, force and energy density profiles of the interface. ► The interfacial tension and thickness has been estimated. ► Our results for water +  n-alkanes, are agree to the experimental behaviour.An analytical expression for the interfacial energy is found by solving a Poisson equation and assuming a Boltzmann distribution of volume elements forming the fluid/liquid system. Interfacial phenomena are treated as a result of the response of a liquid when it makes contact with other fluid phase, in order to reach thermal and mechanical equilibrium. This model gives a quantitative description of the interface, obtaining values for its molar, force and energy density profiles. Also, our model allows the determination of the proportion of the fluids present in the interfacial zone, the values of interfacial tension and thickness. In the case of water +  n-alkanes systems, the tensions are in agreement with the behavior shown by the experimental data. Finally, the values for interfacial thickness predicted from molar density profiles are lower than the range of influence of the elastic energy and elastic field.
Keywords: Interfacial energy; Interfacial tension; Density profile; Fluid–liquid system;

Chemical assembly of TiO2 and TiO2@Ag nanoparticles on silk fiber to produce multifunctional fabrics by Guohong Li; Hong Liu; Hongshi Zhao; Yuqiang Gao; Jiyang Wang; Huaidong Jiang; R.I. Boughton (307-315).
Schematic illustration of the surface-modified TiO2@Ag nanoparticles covalently bonded onto the pre-modified SFF surface.Display Omitted► For the first time, TiO2 and TiO2@Ag nanoparticles are chemical bonded onto silk fibroin fabric. ► The functionalized silk fibroin fabric is endowed with a high UV protection capability, excellent anti-bacterial action, a high photocatalytic and self-cleaning capability. Owing to the strong chemical bonding strength, long term durable effects are obtained. ► The biggest advantage of this simple technology is the adoption of it into the traditional anti-wrinkle finishing technology in textiles, so it is easily scaled up.A carefully designed surface modification technique for the manufacture of multifunctional silk textile nanocomposite materials is successfully developed by the functionalization of silk with TiO2 and TiO2@Ag nanoparticles (NPs). The NPs are assembled onto a silk substrate through covalent linkages, including enediol ligand–metal oxide bonding, resin dehydration and the acylation of silk. Owing to the strong chemical bonding, silk fibroin fabric (SFF) and the NPs form a stable composite system. The functionalized SFF, especially TiO2@Ag NP-functionalized SFF are endowed with remarkable UV protection properties, and an efficient anti-bacterial capability toward Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa. Furthermore, the nearly total photodegradation of methylene orange (MO) under UV illumination illustrates that functionalized SFF possesses high photocatalytic and self-cleaning capability. This multifunctional silk material satisfies the market demand for natural “smart” products, and is a promising practical material for use in the textile industry, hospital sterilization and environmental cleanup.
Keywords: Silk; TiO2 and TiO2@Ag nanoparticles; UV protection; Anti-bacterial; Self-cleaning;