Journal of Colloid And Interface Science (v.375, #1)

Cover 1 (OFC).

On the thermodynamics of biomolecule surface transformations by Stefania Federici; Giulio Oliviero; Daniele Maiolo; Laura E. Depero; Italo Colombo; Paolo Bergese (1-11).
Display Omitted► We have developed a general thermodynamic model for biomolecule surface transformations. ► The model leads to a modified law of mass action for surfaces. ► The predictive value of this thermodynamic approach is tested on typical examples. ► Featured examples include biological-inorganic flat and nanoparticle interfaces.Biological surface science is receiving great and renewed attention owing the rising interest in applications of nanoscience and nanotechnology to biological systems, with horizons that range from nanomedicine and biomimetic photosynthesis to the unexpected effects of nanomaterials on health and environment. Biomolecule surface transformations are among the fundamental aspects of the field that remain elusive so far and urgently need to be understood to further the field. Our recent findings indicate that surface thermodynamics can give a substantial contribution toward this challenging goal. In the first part of the article, we show that biomolecule surface transformations can be framed by a general and simple thermodynamic model. Then, we explore its effectiveness by addressing some typical cases, including ligand–receptor surface binding, protein thin film machines, nanomechanical aspects of the biomolecule–nanoparticle interface and nanomechanical biosensors.
Keywords: Thermodynamics; Biomolecules; Surfaces; Molecular-recognition; Molecular machines; Nanoparticles self-assembly; Biosensors;

Display Omitted► Rh and Pd sols were generated in mixtures of water and an organic solvent. ► Particle size was inversely proportional to cosolvent concentration. ► Sol stability depended nonlinearly on cosolvent concentration. ► Protecting agents used ordinarily in 100% aqueous dispersion media were shown to be mostly effective in the mixed media. ► Adsorption of CO decreased as cosolvent concentration was increased.A series of polymer-protected rhodium and palladium sols were generated in mixed (organic/aqueous) dispersion media. Protecting polymers used were PAA, PVP, PVA and an oligosaccharide-based protecting agent, arabinogalactan. This is the first systematic study of colloids generated in mixed solvent dispersion media with these protecting agents. The sols were characterized by TEM, UV/Vis spectrophotometry and Photon Correlation Spectroscopy (PCS). In general, the macroscopic stability of the sols depended on the protecting agent/organic cosolvent combination used, with a nonlinear dependence on cosolvent concentration. Observed sol stabilities correlated well with pre-existing hydrodynamic data for the protective polymers, e.g. radius of gyration data. Average particle size and polydispersity of all sols examined decreased as cosolvent concentration increased, with actual cosolvent concentration, protecting agent and reducing agent used influencing the extent of decrease. Sol particle sizes ranged from 0.8 nm to 6.0 nm with sol turbidities decreasing in parallel with the particle sizes. Hydrodynamic sizes (from PCS) tended to reflect the sols’ macroscopic stabilities. FTIR studies using adsorbed CO as a spectroscopic surface probe indicated decreases in the ν(CO)ads stretching frequency with an increase in cosolvent concentration due to competitive adsorption of CO with the cosolvent molecules on the metal colloid surfaces.
Keywords: Sol; Colloids; Polymers; Stability; Metals; Mixed media; PCS; FTIR; TEM;

Display Omitted► Mixing an anionic dye pyranine and a cationic polyelectrolyte. ► Colloidal structure can be tuned by pH. ► Sheet-like or spherical colloids are found. ► Fluorescence properties of the complex depends on colloidal structure and pH.Complexes of dyes and polyelectrolytes have found widespread use in a variety of functional materials and interfaces. Here it is found that upon mixing the anionic dye pyranine and a cationic polyelectrolyte, poly(allylamine-hydrochloride), two different colloidal structures may form. Above a certain concentration of anionic dye, crosslinking of the polyelectrolyte is initiated, and the formation of sheet-like colloidal structures was observed. Addition of hydroxyl ions resulted in the formation of micron-sized spherical colloids. It was also found that the colloidal shape transition was accompanied by a significant red-shift in the fluorescence emission. Combining fluorescence measurements with studies of the particle size with time, it was found that red-shift was related to the crosslinking of the dye and the polyelectrolyte, and was not influenced significantly by the aggregation and particle growth. Further information about the colloidal behavior and stability was obtained by letting droplets dry and follow the kinetics of this process. It was found that the particles collapsed near the contact line and formed a ring deposit, in agreement with previous studies. However, unlike previous studies, the thickness of the ring deposit did not grow significantly with time, due to the peculiar process of formation found here.
Keywords: Polyelectrolyte; Anionic dye; Colloid; Fluorescence;

Fabrication of small-sized silver NPs/graphene sheets for high-quality surface-enhanced Raman scattering by Hong Zhao; Honggang Fu; Tianshou Zhao; Lei Wang; Taixing Tan (30-34).
Display Omitted► Ag nanoparticles supported on graphene nanosheets are fabricated via etching Cu template. ► The used graphene is prepared via an in situ generating template route. ► The obtained Ag nanoparticles have small size and high dispersion. ► Distinctive SERS activity is due to small size of Ag and interfacial action. ► The discovery will expand the application of small-sized Ag to SERS.In this paper, small-sized and highly dispersed Ag nanoparticles (NPs) supported on graphene nanosheets are fabricated via a strategy for etching a copper template with Ag+. Firstly, big-sized Cu NPs are supported on graphene, and then the small-sized and highly dispersed Ag NPs are supported on graphene by replacement reaction, mainly making use of graphene passing electrons between Cu and Ag+. The graphene used in the experiment is prepared by in situ self-generating template and has good dispersion, excellent crystallinity and little defects. Thus, in the process of Ag/graphene synthesis, there is no any intervention of surfactant, which ensures that SERS activity sites have not been passivated. And, the little defects of graphene benefit the excellent conductivity of graphene and ensured the replacement reaction between Cu and Ag+. The obtained material exhibits significant high-quality and distinctive SERS activity. Especially, a serial new peak of p-aminothiophenol (PATP) is observed, this is suggested two reasons: one is “surface geometry” of the PATP on small-sized Ag NPs and another is the charge-transfer between Ag and graphene.
Keywords: Surface-enhanced Raman scattering; Ag nanoparticles; Graphene; p-Aminothiophenol;

Display Omitted► Polymer stabilised graphene nanoparticles used in multilayers. ► Layer-by-layer build-up dependent on the pH of the solution. ► Complete coverage was achieved after five bi-layers of graphene and polyelectrolyte. ► Kinetics of the adsorption process monitored using QCM.Exfoliated graphene particles stabilised by the cationic polyelectrolyte polyethyleneimine (PEI) were used in conjunction with an anionic polyelectrolyte, poly(acrylic acid), to construct multilayers using the layer-by-layer technique on a silica substrate. In the first adsorption step, the surface excess of the cationic graphene was dependent on the overall charge on the nanoparticle which in turn can be tuned through modifying solution pH as PEI has weakly ionisable charged amine groups. The adsorbed amount onto the silica surface increased as the solution pH increased. Subsequently, a layer of PAA was adsorbed on top of the cationic graphene through electrostatic interaction. The multilayer could be assembled through this alternate deposition, with the influence of solution conditions investigated. The pH of the adsorbing solutions was the chief determinant of the overall adsorbed amounts, with more mass added at the elevated pH of 9 in comparison with pH 4. Atomic force microscopy confirmed that the graphene particles were adsorbed to the silica interface and that the surface coverage of the disc-like nanoparticles was complete after the deposition of five graphene-polyelectrolyte bi-layers. Furthermore, the graphene nanoparticles themselves could be modified through the consecutive addition of the oppositely charged polymers. A multilayered assembly of negatively charged graphene sheets modified with a bi-layer of PEI and PAA was also deposited on a silica surface with adsorbed PEI.
Keywords: Polyelectrolyte; Graphene; Adsorption; Zeta potential; Atomic force microscopy; Layer-by-layer; Quartz crystal microbalance;

Display Omitted► A desolvation method is developed for self-assembly of nanoparticles from HGPCP. ► The size of nanoparticles is concentration dependent. ► The nanoparticles exhibit highly thermal stability and fluorescent emission. ► The self-assembly is driven by hydrogen bonds with participation of water molecules.Novel organic nanoparticles self-assembled from the hexa[p-(carbonyl glycin methyl ester) phenoxy] cyclotriphosphazene (HGPCP) were prepared by a simple solution method. The as-prepared nanoparticles were extensively characterized by SEM, TEM, XRD, TGA, and fluorescence spectrum. The size of nanoparticles was increased with increasing the HGPCP concentration in solution. The effect of reaction conditions on the particle size and stability was further investigated. Based upon the experimental results, a growth mechanism was proposed for the formation of the nanoparticles. The obtained nanoparticles were highly thermal stable and exhibited strong fluorescent emission, which could be potential candidates for drug-loading carriers and tracer drug delivery.
Keywords: Hexa[p-(carbonyl glycin methyl ester) phenoxy] cyclotriphosphazene; Nanoparticle; Self-assembly; Fluorescent emission; Hydrogen bond;

Using particle tracking to probe the local dynamics of barley β-glucan solutions upon gelation by Thomas Moschakis; Athina Lazaridou; Costas G. Biliaderis (50-59).
Display Omitted► The sol–gel transition of aqueous barley β-glucan solutions upon ageing was studied. ► Particle tracking microrheology (PTM) successfully measured spatial heterogeneities. ► PTM had higher sensitivity than bulk rheology. ► PTM detected structural changes before registered by bulk rheology.The sol–gel transition of aqueous barley β-glucan solutions which undergo gelation with ageing has been studied by conventional bulk rheology, phase contrast microscopy and particle tracking microrheology. Characterisation of the primary structure of the β-glucan isolate was carried out by enzymic methods and HPLC. The Brownian diffusion of fluorescent microspheres (0.75 μm diameter, carboxylate-coated particles) was used to probe the spatial mechanical properties of the gelling systems at the scale of microns; the potential use of passive particle tracking to study biopolymer gelling systems that present spatial heterogeneities is thus explored. For the β-glucan gels cured at 25 °C both microrheology and bulk rheology revealed that with increasing the polysaccharide concentration the gelation time decreased, while the gelation rate and gel strength of the barley β-glucan gels increased. The particle tracking method had higher sensitivity and could map molecular ordering and structural heterogeneities in the evolving polysaccharide network at a micro-level. That is, different size pores were generated upon ageing with regions of depleted or less amount of β-glucan molecules. Furthermore, this method could detect changes in the fine structure of the system before such events can be registered by bulk rheological measurements; i.e. microheterogeneity and aggregation of β-glucan chains were revealed by particle tracking at earlier temporal stages of the experiment.
Keywords: β-Glucans; Particle tracking microrheology; Gelation; Microstructure;

Optical response of Cu clusters in zeolite template by Catalina López-Bastidas; Vitalii Petranovskii; Roberto Machorro (60-64).
Display Omitted► We study Cu clusters embedded in mordenite zeolite. ► Optical properties via reflectance spectroscopy are obtained. ► Theoretical spectra are calculated using effective field approximation. ► Features in experimental spectra can be understood.Optical properties of Cu clusters embedded in mordenite are studied experimentally and theoretically. In this work we discuss spectral features of the system at various reduction steps and compare then with the results of spectra obtained within a theoretical model. The model employed consists of Cu clusters embedded in a homogeneous matrix. A second model employed introduced further variation considering a three component system where air or water can be present. The macroscopic dielectric response of the system is obtained within the Maxwell Garnett approximation. In this approach the complex non-local in homogeneous dielectric response of the zeolite + copper system is replaced by an effective homogeneous dielectric function. Metallic clusters can occupy specific available cavities in the zeolite framework. The presence of clusters that are smaller than the cavities in which they reside can lead to an air–Cu or water–Cu interface which allows shifts in surface plasmon resonance energies. As observed experimentally the energy of the main resonance is seen to be insensitive to the filling fraction ratios and highly susceptible to the embedding matrix properties. Reflectance spectra have been obtained which can be explained within this model.
Keywords: Zeolite; Cu nanoparticles; Plasmon; Optical properties; Template;

Display Omitted► We present a new three parameter description of fractal aggregates. ► The parameters are the fractal dimension, shape and monomer packing fraction. ► DLCA simulations yield quantitative values for the three parameters. ► The effects of these parameters on the structure factor are described.A three parameter description of fractal aggregates is derived from the pair correlation function of the monomeric units that compose the aggregate. The parameters describe the mass fractal scaling with linear size (the fractal dimension), the packing fraction density of the spherical monomers, and the overall shape of the aggregates. Values for these three parameters are determined for diffusion limited cluster aggregates (DLCAs) in three dimensions. The effects of these parameters are found in terms of measureable quantities in both real and reciprocal space.
Keywords: Fractal aggregates; Fractal dimension; Diffusion limited cluster aggregation (DLCA); Aggregates; Morphology; Agglomerates; Pair correlation function; Structure factor; Packing fraction; Anisotropy;

Facile method for synthesis of hollow porous magnetic microspheres with controllable structure by Bin Liu; Wei Zhang; Qingyun Zhang; Han Zhang; Jing Yu; Xinlin Yang (70-77).
Display Omitted► Hollow porous microspheres with strong magnetization and controllable structure. ► Electrostatic self-assembly between Fe3O4 nanoparticles and polymer microsphere. ► Facilely controlled drug release from hollow magnetic microspheres.Hollow porous magnetic microspheres with strong magnetization and controllable structure were prepared via a facile electrostatic self-assembly of the positively charged Fe3O4 nanoparticles onto the surface of the negatively charged poly(N,N′-methylenebisacrylamide-co-methacrylic acid) (P(MBAAm-co-MAA)) microspheres with subsequent removal of the polymer core through calcination at high temperature. The shell thickness was facilely tuned through the ratio between Fe3O4 and polymer, and the void space was conveniently changed through the size of polymer microspheres. The hollow magnetic microspheres possessed high saturation magnetization value (51.38 emu/g) and porous structure with high specific surface area (108.04 m2/g). Based on these properties, the drug loading and release behaviors were investigated, which indicated that the hollow magnetic microspheres exhibited a controlled release process.
Keywords: Hollow magnetic microspheres; Electrostatic self-assembly; Organic–inorganic composite microspheres;

Synthesis of platinum-based binary and ternary alloy nanoparticles in an intense laser field by Yuliati Herbani; Takahiro Nakamura; Shunichi Sato (78-87).
Display Omitted► Alloy nanoparticles are generated by reduction with a femtosecond pulsed laser. ► Precursor solutions are mixtures of the metal ions of interest. ► No reducing agents are added into the mixtures of the metal ions. ► Reduction is due to the reactive species abundantly produced by the laser.Gold–platinum–silver (Au–Pt–Ag) ion mixtures produced nanoparticle alloys with an average particle size of 5 nm after co-reduction of metal ions by femtosecond laser irradiation of aqueous solutions in the presence of ammonia and polyvinylpyrrolidone, which was used as a stabilizer. Alloy formation was confirmed by analyzing the interplanar spacings measured by diffraction techniques; the interplanar spacings obtained showed good agreement with those derived from Vegard’s law. The nanoparticles had elemental composition ratios close to the molar ratios of ions in the mixed solutions, implying a high reduction yield. High-resolution transmission electron microscopy images of nanoparticles revealed that the particles were crystalline and were not phase segregated. Binary nanoparticles from Au–Pt and Ag–Pt immiscible systems were also synthesized to confirm the applicability of this method to ternary systems. The formation of nanoalloys by intense femtosecond laser irradiation was possible due to the fast reduction of the mixed ions by solvated electrons and hydrogen radicals generated in situ during irradiation.
Keywords: Femtosecond laser; Ternary alloy nanoparticles; Aqueous solution; Solvated electrons; Nonlinear optical process;

A micellization study of medium chain length poly(3-hydroxyalkanoate)-based amphiphilic diblock copolymers by Julien Babinot; Jean-Michel Guigner; Estelle Renard; Valérie Langlois (88-93).
Display Omitted► Biocompatible bacterial polyester-based amphiphilic copolymers are synthesized. ► Well-defined micelles ranging from 44 to 90 nm with low polydispersity are obtained. ► The amorphous and hydrophobic nature of the polyester provides very stable micelles. ► The micelles exhibit good stability at physiological ionic strength.In this article, we report the first micellization study of amphiphilic copolymers composed of bacterial medium chain length poly(3-hydroxyalkanoates) (mcl-PHAs). A series of diblock copolymers based on fixed poly(ethylene glycol) (PEG) block (5000 g mol−1) and a varying poly(3-hydroxyoctanoate-co-3-hydroxyhexanoate) (PHOHHx) segment (1500–7700 g mol−1) have been synthesized using “click” chemistry. These copolymers self-assembled to form micelles in aqueous media. The influence of PHOHHx block molar mass on the hydrodynamic size and on the critical micelle concentration (CMC) has been studied using dynamic light scattering and fluorescence spectroscopy, respectively. With increasing PHOHHx length, narrowly distributed micelles with diameters ranging from 44 to 90 nm were obtained, with extremely low CMC (up to 0.85 mg/L). Cryogenic transmission electron microscopy (Cryo-TEM) showed that micelles took on a spherical shape and exhibited narrow polydispersity. Finally, the colloidal stability of the micelles against physiological NaCl concentration has been demonstrated, suggesting they are promising candidates for drug delivery applications.
Keywords: Poly(3-hydroxyalkanoate); Amphiphilic copolymer; Micelles; Click chemistry; Poly(ethylene glycol); Polyester;

Influence of the liquid crystal behaviour on the Langmuir and Langmuir–Blodgett film supramolecular architecture of an ionic liquid crystal by Víctor Pérez-Gregorio; Ignacio Giner; M. Carmen López; Ignacio Gascón; Emma Cavero; Raquel Giménez (94-101).
Display Omitted► A new luminescent ionic liquid crystal (Ipz-2) has been synthesised. ► Ipz-2 exhibits hexagonal columnar mesomorphism in bulk. ► Ipz-2 forms stable Langmuir films at the air–water interface. ► Langmuir–Blodgett (LB) films are obtained by the vertical dipping method. ► Spontaneous formation of large columnar structures in LB films is observed by AFM.A new luminescent ionic liquid crystal, called Ipz-2, has been synthesised and its mesophase behaviour and also at the air–liquid interface has been studied and compared with Ipz, another ionic pyrazole derivative, with a similar molecular structure, previously studied. The X-ray diffraction pattern shows that Ipz-2 exhibits hexagonal columnar mesomorphism, while Ipz adopts lamellar mesophases. Langmuir films of both compounds are flat and homogeneous at large areas per molecule, but create different supramolecular structures under further compression. Ipz-2 Langmuir films have been transferred onto solid substrates, and Atomic Force Microscopy (AFM) images of the Langmuir–Blodgett films have shown that large columnar structures hundreds of nm in diameter are formed on top of the initial monolayer, in contrast with well-defined trilayer LB films obtained for Ipz. Our results show that Ipz-2 has a tendency to stack in columnar arrangements both in liquid crystalline bulk and in Langmuir and Langmuir–Blodgett films.
Keywords: Ionic liquid crystal; 3,5-Diarylpyrazole derivative; Hexagonal columnar mesophases; Langmuir and Langmuir–Blodgett films; Supramolecular structure;

Display Omitted► TiO2 nanoparticles deposited from aqueous suspensions by AC-EPD. ► Water electrolysis is avoided when using alternating fields during EPD. ► Environmental and economic advantages of using water instead of organic solvents.TiO2-nanostructured coatings from aqueous suspensions have been successfully prepared by the application of alternating current (AC) instead of direct current (DC) during electrophoretic deposition (EPD). No organic additives in suspension were required for successful EPD. The quality of the AC-EPD TiO2 coatings in terms of homogeneity and extent of microcracking, upon drying, observed by SEM, was superior to that of DC-EPD coatings made from the same type of suspensions. The main difference between AC- and DC-EPD was the suppression of bubble formation. The absence of water electrolysis at the electrodes can be explained by the particular distribution of the electric field during AC mode, which prevents the nucleation of bubbles. The preparation of TiO2 coatings from aqueous suspension and without the aid of organic stabilizers opens the possibility for co-deposition of sensitive materials such as biomolecules and even cells for biomedical applications, given the high biocompatibility of TiO2. The deposition of TiO2 coatings from aqueous suspensions is also attractive from environmental and economical points of view.
Keywords: Electrophoretic deposition; TiO2 nanoparticles; Alternating current; Coatings;

Synthesis of hollow ellipsoidal silica nanostructures using a wet-chemical etching approach by Henan Zhang; Yi Zhou; Yueru Li; Teresa J. Bandosz; Daniel L. Akins (106-111).
Display Omitted► It is a facile process that directly produces ellipsoidal silica nanoshells. ► It results in ellipsoidal silica nanostructures with dimension less than 100 nm. ► It results in silica structures with controllable shell thickness.We have utilized wet-chemical etching of ellipsoidal silica nanoparticles (ESNs) to form silica nanoshells of a range of elliptical morphologies, with the thicknesses of the ellipsoidal silica nanoshells (ESSs) controlled through variation of synthesis conditions. A mechanism has been proposed to explain how the nanoshells are formed, and we demonstrate that the porosity of the silica ellipsoid plays a role in generating silica shells. Our self-templated, wet-etching approach is an attractive alternate procedure to the approaches presently in existence for the following reasons: (i) it is a facile, one-step process that directly produces ellipsoidal silica nanoshells, while overcoming barriers (such as requirement of removing a solid-core template seed) utilized in many reported chemical etching studies; (ii) it results in ellipsoidal silica nanostructures with dimension less than 100 nm; (iii) with an appropriate etchant, the roughness of the silica shells can be well-controlled; and (iv) it results in tunable, uniform size particles with controllable shell thicknesses. Moreover, the silica materials with the unique structures might be adjusted to meet practical application requirements.
Keywords: Wet-chemical etching; Hollow shells; Ellipsoidal silica nanostructure; Self-templated;

Stepwise dansyl grafting on the kaolinite interlayer surface by Elisa Moretti; Loretta Storaro; Gavino Chessa; Aldo Talon; Emanuela Callone; Klaus Josef Mueller; Francesco Enrichi; Maurizio Lenarda (112-117).
Display Omitted► Dansyl residue was grafted to the internal kaolinite surface by a step-wise process. ► Emission luminescence properties were measured in the solid state. ► Multinuclear MAS-NMR characterization of all intermediates was carried out.Here we describe the step-wise grafting of the fluorophore dansyl chloride on the interlayer aluminol groups of kaolinite. The modified clay was characterized by powder RD, TGA, FT-IR and 27Al, 19Si, 13C MAS-NMR, which confirmed the achievement of the clay functionalization. The photophysical properties of the resulting nanohybrid material were evaluated by photoluminescence excitation and emission measurements.
Keywords: Kaolinite; Hybrid materials; Surface functionalization; Dansyl chloride; Luminescence;

Display Omitted► Parallel 1D chains of CdS nanoparticles were prepared at the air/water interface. ► These nanostructures were produced through one-step synthesis and assembly process. ► 10,12-pentacosadiynoic acid supermolecules in Langmuir monolayers acted as templates. ► The parameters of the nanostructures can be tuned.Regular one-dimensional (1D) parallel chains composed of CdS nanoparticles with cubic zinc blende crystal structure were prepared at the air/water interface via one-step synthesis and assembly process. These nanostructures were produced through an interfacial reaction between Cd2+ ions in the aqueous solution of cadmium acetate and H2S in the gaseous phase under Langmuir monolayers of 10,12-pentacosadiynoic acid (PDA). It was demonstrated that PDA molecules self-assembled into parallelly aligned linear supermolecules at the air/water interface with the aid of π–π interactions and acted as templates for the formation of the superstructures. The experimental conditions including temperature and reaction time have great influences on the superstructure formation and the parameters of the parallel chains.
Keywords: Langmuir monolayer; Air–water interface; CdS nanoparticles; One-dimensional chains;

Highly catalytic spherical carbon nanocomposites allowing tunable activity via controllable Au–Pd doping by Shaochun Tang; Sascha Vongehr; Guorong He; Lan Chen; Xiangkang Meng (125-133).
Display Omitted► This work resolves a problem of doping a submicron matrix internally with Pd NPs. ► The NPs locate inside a shell from beneath the CS’ surface to about 100 nm below. ► We prepared Au–Pd/CS catalysts with Au:Pd atomic ratios varying from 0.4 to 4.6. ► The growth of Au and its location relative to the pre-existing Pd are discussed. ► The catalytic activity of the Au–Pd/CS is 100 times over that of the Pd/CS.We report the synthesis of highly catalytic spherical carbon composite particles with Au–Pd bimetallic nanoparticle doping using a microwave-assisted technique that allows control over the location of the nanoparticles (NPs), putting them into stable interior, but still near-surface locations (within a 100 nm thick shell). First, composite particles with Pd NPs inside of nanoporous carbon spheres (CSs) were synthesized. Subsequent immersion of the composite particles in HAuCl4 solutions containing PVP led to an addition of Au near the Pd. Au–Pd/CS composites with Au:Pd atomic ratios varying from 0.4 to 4.6 were prepared. The growth of Au and its location relative to the carbon’s surface and the Pd are discussed. The catalytic activity towards the reduction of 4-nitrophenol is tunable via the Au:Pd atomic ratio. Optimizing the composition increases the activity a hundredfold over that of the corresponding monometallic Pd/CS. The catalytic activity arises from the synergy between different contributing mechanisms, here especially the interaction between the carbon matrix and metals, metal–metal interfaces, and the hydrogen absorption capabilities of Pd.
Keywords: Carbon composite particles; Gold–palladium; Bimetallic interface; Catalytic activity;

Effects of counter ions of clay platelets on the swelling behavior of nanocomposite gels by Huai-Yin Ren; Meifang Zhu; Kazutoshi Haraguchi (134-141).
Display Omitted► NC gels with monovalent cations showed large swelling and subsequent deswelling. ► Introduction of multivalent cations depressed the swelling–deswelling markedly. ► Intra-clay/cation and inter-clay/cation interactions. ► Reversible absorption/desorption. ► Selective absorption of multivalent cations.The effects of replacing the native Na+ counter ions associated with the clay platelets by various other cations on the swelling behavior of nanocomposite (NC) gels consisting of an organic (polymer)/inorganic (clay) network were investigated. The negative surface charge of the clay platelet conferred an ionic nature on the NC gels making them a type of polyelectrolyte gel; consequently, the swelling behavior of the NC gels was strongly influenced by the valence of the co-existing counter ions. NC gels containing monovalent cations such as Na+, K+ and Li+ exhibited large swellings and subsequent deswelling in water after attaining maximum degrees of swelling. In contrast, introduction of multivalent cations such as Ca2+, Mg2+, and Al3+ into NC gels depressed markedly both the swelling and subsequent deswelling. The decreased swelling and suppressed deswelling with multivalent ions were strongly influenced by the initial gel state and result from the formation of additional cross-links through ionic interactions between the clay platelets and the multivalent cations. Also, the similar swelling behaviors were observed for all NC gels with different clay concentration. Further, reversible absorption/desorption and selective absorption of multivalent cations were observed for the NC gels examined.
Keywords: Nanocomposite gel; Swelling; Clay; Ion exchange; Selective adsorption;

Poly(lactic-co-glycolic acid) as a particulate emulsifier by Catherine P. Whitby; Li Hui Lim; Nasrin Ghouchi Eskandar; Spomenka Simovic; Clive A. Prestidge (142-147).
Display Omitted► Nanoparticles of poly(lactic-co-glycolic acid) are effective Pickering emulsifiers. ► Surface hydrophobicity altered so oil-in-water emulsions are preferentially stabilised. ► Nanoparticle concentration is a key parameter controlling drop size and stability.The structure and stability of emulsions formed in the presence of nanoparticles of poly(lactic-co-glycolic acid) (PLGA) were characterised. From oil–water contact angles on PLGA films, it was deduced that particle surface hydrophobicity is linked to the oil phase polarity. Incorporation of polyvinyl alcohol molecules into the nanoparticle surfaces reduces the particle hydrophobicity sufficiently for oil-in-water emulsions to be preferentially stabilised. PLGA nanoparticles enhance the stability of emulsions formed from a wide range of oils of different polarities. The nanoparticle concentration was found to be a key parameter controlling the average size and coalescence stability of the emulsion drops. Visualisation of the interfacial structure by electron microscopy indicated that PLGA nanoparticles were located at the drop surfaces, evidence of the capacity of these particles to stabilise Pickering-type emulsions. These results provide insights into the mechanism of PLGA nanoparticle stabilisation of emulsions.
Keywords: Particle-stabilised emulsion; Pickering emulsion; Poly(lactic-co-glycolic acid) nanoparticles;

Display Omitted► Micellization of Sulfobetaine Zwitterionic Gemini Surfactants is entropy-driven. ► The enthalpy–entropy compensation temperature is (302 ± 3) K. ► The contribution of enthalpy increases with temperature. ► A longer spacer chain length can enhance the formation and stability of micelles. ► Thermodynamic results are similar to the anionic rather than cationic surfactants.In this article, the validity and accuracy of the free energy perturbation (FEP) model used in a previous article for ionic liquid-type Gemini imidazolium surfactants (ILGISs) is further evaluated by using it to model the Enthalpy–entropy compensation of Sulfobetaine-type Zwitterionic Gemini Surfactants (SZGSs), with different carbon atoms of the hydrophobic group or the spacer chain length, in aqueous solutions. In the FEP model, the Gibbs free energy contributions to the driving force for micelle formation are computed using hydration data obtained from molecular dynamics simulations. According to the pseudo-phase separation model, the thermodynamic properties of micellization in aqueous solutions for SZGS were discussed. The results show that the micellization of SZGS in aqueous solutions is a spontaneous and entropy-driven process. It is linearly Enthalpy–entropy compensated and different from the micelle formation of ILGIS but similar to anionic surfactants. The compensation temperature was found to be (302 ± 3) K which was lower than ILGIS. As the temperature rises, the micellization is easy initially but then becomes difficult with the unusual changes of enthalpy values from positive to negative. The contribution of entropy change to the micellization tends to decrease but the contribution of enthalpy change tends to increase. In particular, as the number carbon atoms in the alkyl chains and spacer chains are increased, the thermodynamic favorability and stability of the micelles both increase.
Keywords: Sulfobetaine-type Zwitterionic Gemini Surfactants; Thermodynamics; Free energy perturbation; Solvation free energy; Enthalpy–entropy compensation;

Display Omitted► Adsorptive removal of arsenic from water by MWCNT–ZrO2. ► MWCNT–ZrO2 was effective in meeting drinking water standards of 10 μg L−1. ► As(III) and As(V) adsorption described by a pseudo-second order rate equation. ► As(III) and As(V) adsorption fitted both the Langmuir and Freundlich models. ► Higher adsorption capacities than those observed for iron oxide modified sorbents.The adsorptive removal of arsenic from water using a multiwall carbon nanotube–zirconia nanohybrid (MWCNT–ZrO2) is presented. The MWCNT–ZrO2 with 4.85% zirconia was effective in meeting the drinking water standard levels of 10 μg L−1. The absorption capacity of the composite were 2000 μg g−1 and 5000 μg g−1 for As(III) and As(V) respectively, which were significantly higher than those reported previously for iron oxide coated MWCNTs. The adsorption of As(V) on MWCNT–ZrO2 was faster than that of As(III), and a pseudo-second order rate equation effectively described the uptake kinetics. The adsorption isotherms for As(III) and As(V) fitted both the Langmuir and Freundlich models. A major advantage of the MWCNT–ZrO2 was that the adsorption capacity was not a function of pH.
Keywords: Arsenic; Carbon nanotubes; Zirconia; Water; Adsorption; Kinetics;

Display Omitted► The magnetic microsphere with surface dendrimer was synthesized. ► The magnetic microspheres were applied for the adsorption of Cr(VI). ► The effects of conditions on adsorption were investigated. ► The maximum adsorption capacity of Cr(VI) was fitted at 231.8 mg/g.The magnetic poly-(methyl acrylate-divinyl benzene) (MA-DVB) microspheres with micron size were synthesized by modified suspension polymerization method. Through stepwise reaction with methyl acrylate (MA) and ethylenediamine (EDA), the magnetic poly-(MA-DVB) microspheres with surface dendrimer containing amino groups were obtained. The above mentioned magnetic microspheres were applied for the adsorption of hexavalent chromium from aqueous solution. The effects of solution pH value, adsorption temperature, and adsorption and desorption of Cr(VI) were studied. The results showed that the optimum pH value for Cr(VI) adsorption was found at pH = 3, and the adsorption capacity increased with the increase in adsorption temperature. The adsorption equilibrium of Cr(VI) was obtained in about 12 min and more than 98% of adsorbed Cr(VI) were desorbed from the magnetic microspheres in about 30 min using Na2SO4 solution. By fitting the experimental data to Langmuir equation, the maximum capacity for Cr(VI) of magnetic poly-(MA-DVB) microspheres was estimated at 231.8 mg/g.
Keywords: Dendrimer; Hexavalent chromium; Magnetic microspheres; Magnetic separation;

Influence of interfacial water layer on surface properties of silver halides: Effect of pH on the isoelectric point by Nikola Kallay; Tajana Preočanin; Filip Šupljika; Johannes Lützenkirchen; Maja Lovković (167-171).
Display Omitted► Isoelectric points of silver halides are shifted to higher pAg values in acidic environment. ► Water layer at silver halide surfaces is negatively charged in the pH region above 4 causing more negative ζ-potentials. ► Pristine isoelectric points of silver halides were determined at pH = 3.The hypothesis that pH dependent charge of interfacial water affects electrokinetic charge and electrokinetic potential of hydrophobic colloids, but not the (inner) surface potential was tested. It was found that isoelectric points of silver chloride, bromide and iodide shift to the higher pAg values in the acidic solutions, but that surface potential did not depend on pH. Isoelectric points of water at inert surfaces lie in the range 2 < pH < 4. In the neutral environment around pH ≈ 7, the interfacial water is negatively charged due to preferential accumulation of OH ions, with respect to H+ ions, thus increasing the negative electrokinetic charge of silver halide particles. In the acidic region, the isoelectric points of silver halides were shifted to the higher pAg values by 0.5–1.0 pAg units depending on the type of silver halide, as well on the ionic strength of the solution. At pH ≈ 3, the interfacial water is almost uncharged so that electrokinetic charge of silver halide particles is due to adsorption of silver and halide ions only. The conclusion was supported by mass titration experiments. Consequently, the electroneutrality points of silver halide surfaces correspond to values obtained in the acidic media. For silver chloride, pAgeln  = 5.3; for silver bromide, pAgeln  = 5.5; and for silver iodide, pAgeln  = 4.8.
Keywords: Electrokinetics; Silver chloride; Silver bromide; Silver iodide; Interfacial water; pH; Isoelectric point;

Display Omitted► A new catalyst TiO2–(PW12/TH) n was successfully prepared. ► The catalyst shows high photocatalytic activity under visible light. ► The catalyst can be recycled easily.Multilayer films (PW12–TH) n (PW12  =  PW 12 O 40 3 - , TH = thionine) were immobilized on porous anatase TiO2 microspheres by layer-by-layer (LbL) self-assembly method. The porous structure of TiO2 was confirmed by transmission electron microscopy (TEM). Scanning electron microscopy (SEM) showed that TiO2 template particles had a round shape with an average diameter of 250 nm. The composite films were characterized by FTIR spectroscopy, UV diffuse reflectance spectroscopy and XRD spectroscopy. The results confirmed the successful immobilization of (PW12–TH) n composite films onto TiO2 microspheres, and the growth of PW12–TH layer pair was uniform. SEM and TEM were also used to characterize the morphology. When PW12–TH composite films were assembled on the template, the surface became rougher with the increasing number of layer pair. The lattice fringe of TiO2 became weaker when immobilized (PW12–TH) n . The photocatalytic properties of the microspheres toward a rhodamine B (RhB) solution were investigated under visible light irradiation. The combination of TiO2 and PW12 showed an excellent photocatalytic performance. Both TH sensitization and PW12 adsorption played important roles during the process of photocatalysis. Moreover, the catalytic property and reusability of as-prepared catalyst were relevant to the number of PW12–TH bilayer. The kinetics of the photodecomposition to rhodamine B followed the first-order reaction.
Keywords: Layer-by-layer; Thionine; TiO2; Photocatalysis; Film;

Close-packed monolayers of charged Janus-type nanoparticles at the air–water interface by Volodymyr Sashuk; Robert Hołyst; Tomasz Wojciechowski; Marcin Fiałkowski (180-186).
Display Omitted► Novel approach to obtain monolayer of charged nanoparticles at air–water interface. ► Charged nanoparticles possess Janus-type structure. ► Positively and negatively charged nanoparticles are employed. ► Monolayer can be compressed to form stable close-packed array of nanoparticles. ► Langmuir–Blodgett technique used to transfer monolayer on solid substrate.We present a new method to obtain close-packed monolayers composed of noble metal nanoparticles (NP) possessing well-defined permanent charge of either sign. The method is based on the fact that ligands forming the protecting layer exhibit ability to rearrange at the NPs surface. We demonstrate that if the protecting layer is composed of a mixture of hydrophobic and hydrophilic charged ligands in appropriate proportion, the NP exhibits properties of a Janus-type particle with one of the hemispheres hydrophilic and the other hydrophobic. Such amphiphilic NPs self-assemble into a monolayer of well defined surface charge at the air–water interface. Due to strong stabilizing effect of the lateral electrostatic repulsions, such monolayer can be compressed to form close-packed hexagonal structure, and then easily transferred onto a solid substrate with the Langmuir–Blodgett technique.
Keywords: Hexagonally close-packed monolayer; Janus nanoparticle; Charge; Air–water interface; Langmuir–Blodgett technique; Self-assembly;

Display Omitted► Measurement of residual oil phase cluster size distribution in an oil-wet sandstone. ► Measurement of morphology of residual clusters. ► Demonstration of clear difference between residual oil clusters in water-wet and oil-wet rock.We imaged an oil-wet sandstone at residual oil saturation (S or) conditions using X-ray micro-tomography with a nominal voxel size of (9 μm)3 and monochromatic light from a synchrotron source. The sandstone was rendered oil-wet by ageing with a North Sea crude oil to represent a typical wettability encountered in hydrocarbon reservoirs. We measured a significantly lower S or for the oil-wet core (18.8%) than for an analogue water-wet core (35%). We analysed the residual oil cluster size distribution and find consistency with percolation theory that predicts a power-law cluster size distribution. We measure a power-law exponent τ  = 2.12 for the oil-wet core which is higher than τ for the water-wet system (τ  = 2.05), indicating fewer large clusters in the oil-wet case. The clusters are rough and sheet-like consistent with connectivity established through layers in the pore space and occupancy of the smaller pores; in contrast the clusters for water-wet media occupy the centres of the larger pores. These results imply less trapping of oil, but with a greater surface area for dissolution. In carbon storage applications, this suggests that in CO2-wet systems, capillary trapping is less significant, but that there is a large surface area for dissolution and reaction.
Keywords: Residual trapping; Residual oil saturation; Oil-wet; X-ray micro-tomography;

Atmospheric pressure plasma induced grafting of poly(ethylene glycol) onto silicone elastomers for controlling biological response by Raechelle A. D’Sa; Jog Raj; M. Ann S. McMahon; David A. McDowell; George A. Burke; Brian J. Meenan (193-202).
Display Omitted► We have shown SE can be successfully functionalised by DBD treatment. ► Successful plasma induced graft polymerisation PEGMA macromonomers was achieved. ► Mammalian cell adhesion was decreased on these surfaces. ► Bacterial cell adhesion was not decreased on these surfaces. ► The mechanism of mammalian cell resistance does not correlate to bacterial cell resistance.This study investigates the role that surface functionalisation of silicone elastomer (SE) by atmospheric pressure plasma induced graft immobilisation of poly(ethylene glycol) methyl ether methacrylate (PEGMA) plays in the attendant biological response. SE is used in modern ophthalmic medical devices and samples of the material were initially plasma treated using a dielectric barrier discharge reactor (DBD) to introduce reactive oxygen functionalities, prior to in situ grafting of two molecular weights of PEGMA (MW 1000 Da: PEGMA1000, MW 2000 Da: PEGMA2000). The variously processed surfaces were characterised by water contact angle analysis, X-ray photoelectron spectroscopy, time-of-flight secondary ion mass spectrometry and atomic force microscopy. Lens epithelial cells were then cultured on the PEGMA grafted SE surfaces. It was found that cells on the pristine surface were not well spread and had shrunken morphology. On the DBD pre-treated surfaces, the cells were well spread. On the PEGMA1000 surface, the cells displayed evidence of shrinkage and were on the verge of detaching. Remarkably, on the PEGMA2000 surface, no cell adhesion was detection. Bacterial adhesion to the surfaces was studied using Staphylococcus aureus NTC8325. There was no difference in the number of bacteria adhering to any of the surfaces studied.
Keywords: Non-fouling; Poly(ethylene glycol); Plasma polymerisation; Surface grafting; Surface modification; Silicone elastomer; Cell response; Bacterial response;

Strong magnetic field effects on solid–liquid and particle–particle interactions during the processing of a conducting liquid containing non-conducting particles by Z.H.I. Sun; X. Zhang; M. Guo; L. Pandelaers; J. Vleugels; O. Van der Biest; K. Van Reusel; B. Blanpain (203-212).
Display Omitted► We provide a detailed interpretation of the magneto-hydrodynamic interaction force. ► The magneto-hydrodynamic interaction force depends on the flow field. ► Strong magnetic field effects on drag forces are evaluated for the first time reported. ► Interaction of micrometer-sized particles can be controlled by using a magnetic field.The behavior of micrometer-sized weak magnetic insulating particles migrating in a conductive liquid metal is of broad interest during strong magnetic field processing of materials. In the present paper, we develop a numerical method to investigate the solid–liquid and particle–particle interactions by using a computational fluid dynamics (CFDs) modeling. By applying a strong magnetic field, for example, 10 Tesla, the drag forces of a single spherical particle can be increased up to around 15% at a creeping flow limit. However, magnetic field effects are reduced when the Reynolds number becomes higher. For two identical particles migrating along their centerline in a conductive liquid, both the drag forces and the magnetic interaction will be influenced. Factors such as interparticle distance, Reynolds number and magnetic flux density are investigated. Shielding effects are found from the leading particle, which will subsequently induce a hydrodynamic interaction between two particles. Strong magnetic fields however do not appear to have a significant influence on the shielding effects. In addition, the magnetic interaction forces of magnetic dipole–dipole interaction and induced magneto-hydrodynamic interaction are considered. It can be found that the induced magneto-hydrodynamic interaction force highly depends on the flow field and magnetic flux density. Therefore, the interaction between insulating particles can be controlled by applying a strong magnetic field and modifying the flow field. The present research provides a better understanding of the magnetic field induced interaction during liquid metal processing, and a method of non-metallic particles manipulation for metal/ceramic based materials preparation may be proposed.
Keywords: Strong magnetic field; Conducting liquid; Magneto-hydrodynamics; Interaction;

Display Omitted► Ways to stabilize dispersions of microcapsules are described. ► The microcapsules need to be highly charged in order to give a stable suspension. ► X-ray photoelectron spectroscopy is used to assess the degree of dissociation.Poly(methyl methacrylate) microcapsules have been prepared using the solvent evaporation technique with poly(methacrylic acid) (PMAA) as dispersant. The charge, swelling and desorption of PMAA from the microcapsules after treating the suspension with base have been followed using microelectrophoresis, X-ray photoelectron spectroscopy and quartz crystal microbalance with dissipation monitoring on model PMMA surfaces. Basic treatment of the microcapsule suspension leads to temporary colloidal stability through the introduction of charges on the PMAA chain. However, the increase in charge causes a continuous desorption of PMAA from the microcapsule surface, eventually leading to aggregation. If instead poly(diallyldimethylammonium chloride) is added to the base treated microcapsule suspension, good colloidal stability is obtained.
Keywords: Quartz crystal microbalance with dissipation monitoring; Microcapsule; Poly(methacrylic acid); Colloidal stability; Degree of dissociation; X-ray photoelectron spectroscopy;