Journal of Colloid And Interface Science (v.332, #2)

The objective of this research was to fabricate stable and environmentally sensitive (PNIPAAm/ALG) n microcapsules via layer-by-layer (LbL) technique. The structure, thermosensitive and pH-sensitive properties of the microcapsules were characterized by transmission electron microscopy (TEM), confocal laser scanning microscopy (CLSM) and atomic force microscopy (AFM), individually. MnCO3 microparticles and melamine formaldehyde (MF) microparticles were used as templates separately. The microcapsules from MnCO3 cores were stable over a large pH range with thermosensitive and pH-sensitive properties, while those from MF particles were unstable in basic solutions. To the end, ALG and PNIPAAm were adsorbed on recrystallized taxol alternatively, which obviously prolonged the release time of taxol above lower crystal solution temperature (LCST) of PNIPAAm.Thermosensitive and pH-sensitive microcapsules of (PNIPAAm/ALG) n were fabricated via layer-by-layer (LbL) technique. The microcapsules from MnCo3 cores were stable over a large pH range due to the cross-linking of Mn2+.
Keywords: Microcapsules; Thermoresponsive; pH-responsive; Manganese ions; Drug release;

New modified chitosan-based adsorbent for defluoridation of water by Sneha Jagtap; Dilip Thakre; Snehal Wanjari; Sanjay Kamble; Nitin Labhsetwar; Sadhana Rayalu (280-290).
In the present study, the metal-binding property of chitosan is used to incorporate titanium metal and applied as an adsorbent for fluoride adsorption. Titanium macrospheres (TM) were synthesized by a precipitation method and characterized by FTIR, SEM, and XRD. The Langmuir and Freundlich adsorption models were applied to describe the adsorption equilibrium and the adsorption capacities were calculated. Thermodynamic parameters of standard free energy change ( Δ G ○ ), standard enthalpy change ( Δ H ○ ), and standard entropy change ( Δ S ○ ) were also calculated. The effects of various physico-chemical parameters such as pH, initial concentration, adsorbent dose, and the presence of coexisting anions were studied. The fluoride uptake was maximum at neutral pH 7 and decreased in acidic and alkaline pH. The presence of coexisting anions has a negative effect on fluoride adsorption. TM was found to have very fast kinetics in the first 30 min and then the rate slowed down as equilibrium was approached. A comparison of fluoride removal in simulated and field water shows a high adsorption capacity in simulated water.Chitosan is able to coordinate with metals because of a high concentration of an amino functional group. TM shows a very high fluoride adsorption capacity and affinity for fluoride compared to chitosan.
Keywords: Defluoridation; Chitosan; Titanium macrospheres; Fluoride adsorption; Effect of coexisting anions and pH;

Mixed adsorption layers of 0.1 M tert-butanol–tetramethylthiourea at the interface of Hg/aqueous perchlorate solutions by Dorota Gugała-Fekner; Dorota Sieńko; Jolanta Nieszporek; Małgorzata Klin; Jadwiga Saba (291-297).
The analysis of the course of differential capacity curves in the case of mixed adsorption layers: TMTU–TB points to a clear domination of TMTU in the formation of adsorption equilibria.The electrosorption behavior of tetramethylthiourea (TMTU) on a mercury electrode from 1.0, 0.5, and 0.1 M NaClO4 solutions containing 0.1 M tert-butanol (TB) is described by means of adsorption isotherm constants. The adsorption parameters for the double layer were calculated from a double-layer differential capacity measurement extrapolated to zero frequency. The values of the relative surface excess increase along with the concentration of NaClO4. It seems that the adsorption of TMTU is determined by an interaction between adsorbed molecules. The presence of TB in the adsorption layer distinctly influences the parameters of the inner layer.
Keywords: Differential capacity; Electrostatic parameters; Mixed adsorption layer; Tetramethylthiourea; tert-Butanol;

The synthesis of needle/fibrous particles of analogue of heulandite with particle diameter of 0.08 μm, length 4–8 μm and high specific surface area (478 m2 g−1) with cation exchange capacity (3.27 mequiv g−1) have been achieved. The heulandite needles were obtained by using inorganic salts as a source for silicon and aluminum in the hydrothermal synthesis of the material. Alkalinity of the medium played an important role in the formation of heulandite fibers, as it affects the nucleation rate of zeolite synthesis. The analogue of heulandite was characterized using spectroscopic, thermal analysis, scanning and adsorption techniques. After mechanical grinding of crystals of heulandite, obtained powder was used for the study of radionuclide recovery from aqueous waste. The adsorption experiments were carried out under batch process with, pH of medium, amount of sorbent, time of contact between sorbate and sorbent, metal ion concentration and temperature as the variables. The adsorption was strongly dependent on pH of the medium and the uptake of all the metal ions increased from pH 1.0 to 9.0 and the maximum sorption was noticed in the pH range of 5.0–7.0. The optimum condition for these metal ions (Th(IV), Eu(III), Sm(II), and Fe(III)) sorption on self synthesized analogue of heulandite was; 0.001 N metal ion concentration, equilibration time of 4 h, 100 mg sorbent dose and 313–323 K temperature. This sorption process is fit to both Langmuir and Freundlich sorption isotherm. Thermodynamic studies predict the endothermic and spontaneous nature of the same.Synthetic analogue of heulandite having crystallites of needle/rode like shapes act as prominent sorbent for the removal of toxic metal ions from aqueous waste.
Keywords: Analogue; Heulandite; Sorption; Isotherm; Morphology;

The adsorption of I was determined to be an outer-sphere process from ETLM analysis, which was consistent with independent XANES observation of I adsorbed on HFO.A deficiency in environmental iodine can cause a number of health problems. Understanding how iodine is sequestered by materials is helpful for evaluating and developing methods for minimizing human health effects related to iodine. In addition, 129I is considered to be strategically important for safety assessment of underground radioactive waste disposal. To assess the long-term stability of disposed radioactive waste, an understanding of 129I adsorption on geologic materials is essential. Therefore, the adsorption of I on naturally occurring oxides is of environmental concern. The surface charges of hydrous ferric oxide (HFO) in NaI electrolyte solutions were measured by potentiometric acid–base titration. The surface charge data were analyzed by means of an extended triple-layer model (ETLM) for surface complexation modeling to obtain the I adsorption reaction and its equilibrium constant. The adsorption of I was determined to be an outer-sphere process from ETLM analysis, which was consistent with independent X-ray absorption near-edge structure (XANES) observation of I adsorbed on HFO. The adsorption equilibrium constants for I on β-TiO2 and γ-Al2O3 were also evaluated by analyzing the surface charge data of these oxides in NaI solution as reported in the literature. Comparison of these adsorption equilibrium constants for HFO, β-TiO2, and γ-Al2O3 based on site-occupancy standard states permitted prediction of I adsorption equilibrium constants for all oxides by means of the Born solvation theory. The batch adsorption data for I on HFO and amorphous aluminum oxide were reasonably reproduced by ETLM with the predicted equilibrium constants, confirming the validity of the present approach. Using the predicted adsorption equilibrium constants, we calculated distribution coefficient ( K d ) values for I adsorption on common soil minerals as a function of pH and ionic strength.
Keywords: Adsorption; HFO; Oxides; Iodide; Acid–base titration; ETLM; XANES;

A new ATRP initiator, 11-(2-bromoisobutyrate)-undecyl-1-phosphonic acid, has been synthesized and grafted as a film on a mechanically polished stainless steel (ASI304) substrate. Molecular integrity of the grafted initiator in the film, alkyl chain ordering, wettability were determined by X-ray photoelectron spectroscopy, infrared, and water contact angles. Polystyrene, poly(methyl methacrylate) and diblock copolymer (polystyrene-b-poly(methyl methacrylate)) brushes have been grafted from the flat stainless steel surfaces through surface-initiated atom transfer radical polymerization (ATRP) and characterized to check the effectiveness of the new initiator for future uses in surface-initiated ATRP.
Keywords: ATRP; Phosphonic acids; SAMs;

Polystyrene nanocomposites using hybrid organic inorganic (O/I) layered double hydroxide (LDH) and 4[12-(methacryloylamino)dodecanoylamino]benzenesulfonate (MADABS) interleaved molecules were studied as a function of the filler miscibility, dispersion, and the rheological behavior. Incorporation of the I/O filler gave rise to an expanded intercalated PS nanocomposite structure, while an immiscible structure was obtained after a thermal pre-treatment. However the utmost non-linear viscoelasticity in the low-ω region was obtained from the immiscible PS nanocomposite structure. Indeed, the presence of a sub-micrometer percolated structure was here depicted resulting in a jammed structure that progressively changed the typical low-frequency Newtonian flow behavior of PS to a shear-thinning behavior against the filler percentage, having as a consequence to restrict the plastic deformation in the low-ω region by obstructing polymer chain motion. From several characterizations XRD, TEM, and rheology, we demonstrated the presence of LDH agglomerates in spite of PS chain crawling in between the layers, whereas the apparent immiscible structure was composed of well dispersed LDH tactoids forming a three-dimensional percolated network. The gel-like behavior illustrated by the frequency power law dependence of the complex viscosity | η ∗ | ∝ ω n , n ≈ − 0.75 at 10 wt% of MADABS/LDH hybrid filler was then explained by the interconnected and concatenated hybrid LDH platelets domains developing an interfacial attrition with PS chains.Interfacial attrition developed between layered double hydroxide platelets organo-modified by monomer surfactant and polystyrene was characterized by rheology under melt polymer condition.
Keywords: Layered double hydroxide; Filler for polymer; Rheology; Interfacial attrition;

New biodegradable materials produced by ring opening polymerisation of poly(l-lactide) on porous silicon substrates by Steven J.P. McInnes; Helmut Thissen; Namita Roy Choudhury; Nicolas H. Voelcker (336-344).
In this paper, we describe for the first time the preparation of biodegradable inorganic/organic hybrid materials by grafting poly(l-lactide) (PLLA) from porous silicon (pSi) films and microparticles. To graft a PLLA layer from pSi, tin(II) 2-ethylhexanoate catalysed ring opening polymerisation was performed using pSi surface-bound hydroxyl groups as initiators. Chemical surface characterisation by means of diffuse reflectance infrared spectroscopy, X-ray photoelectron spectroscopy and water contact angle measurements confirmed the presence of the PLLA film. Furthermore, atomic force microscopy demonstrated the formation of PLLA nanobrushes on the pSi surface. We also ascertained by interferometric reflectance spectroscopy that the PLLA layer successfully slowed down the corrosion of the porous silicon layer in aqueous medium. Finally, thermal gravimetric analysis showed weight loss transitions that closely resemble the expected decomposition peak for low molecular weight PLLA. We believe that biodegradable hybrid materials like the ones presented here will find uses in tissue engineering and drug delivery, for example in applications where complex degradation profiles are required that cannot be achieved with one type of material alone.Biocompatible thin films of poly(l-lactide) grafted to porous silicon films and microparticles via surface initiated ring opening polymerisation from surface bound hydroxyl initiator groups.
Keywords: Surface initiated ring opening polymerisation; Polylactides; Porous silicon; Biodegradable;

Interactions between bovine serum albumin and alginate: An evaluation of alginate as protein carrier by Yinyan Zhao; Fuyue Li; M. Teresa Carvajal; Michael T. Harris (345-353).
The intermolecular interactions between the model protein, bovine serum albumin (BSA) and a biocompatible polysaccharide, sodium alginate, have been investigated. Both the native BSA and the heat pre-denatured BSA were utilized to study, in parallel, the effect of protein conformational change during the protein–alginate complex formation. In this work, a comparison was performed between the native BSA and the heat-denatured BSA incubated sodium alginate mixtures by using zeta potential analyzer, dynamic light scattering (DLS) and turbidimetric analysis of the systems in combination with protein conformational tools, Fourier transform infrared spectroscopy (FT-IR) and size exclusion chromatography (SE-HPLC). The experimental results demonstrate that the intermolecular chain associations were formed between alginate chains and protein molecules in either the native form or the heat pre-denatured form, mainly driven by the electrostatic interactions between the oppositely charged amino acids and the anionic polysaccharide macromolecules. However, the majority of BSA was recovered from the dissociation of protein–alginate complexes and maintained its secondary structure and conformational property. Therefore, alginate is promising as a bioactive compound carrier.Investigation of intermolecular interaction between alginate and BSA in both native form and heat pre-denatured form.
Keywords: Intermolecular interactions; Complexes; Denaturation; Carboxyl groups; Dissociation;

Characterization of floc size, strength and structure in various aluminum coagulants treatment by Yan Wang; Bao-Yu Gao; Xiu-Ming Xu; Wei-Ying Xu; Gui-Ying Xu (354-359).
Flocs generated in various aluminum coagulants treatment exhibit difference in size, strength and structure. The formation, breakage and re-formation of flocs were investigated by using a laser diffraction instrument (Malvern Mastersizer 2000, Malvern, UK). Different Al coagulants – conventional Al salt (AlCl3), polyaluminum chloride (PAC-1) and the purified polyaluminum chloride (PAC-2) – were investigated for the coagulation of humic acid (HA). The results showed the properties of HA flocs depend on which species of aluminum used. The monomeric and dimeric aluminum species (denoted as Almono) formed the largest and strongest HA flocs with longest growth time. The HA flocs formed by Al13O4(OH)7+ 24 (Al13 for short) is the smallest and weakest. The properties of HA flocs made it possible to investigate the relationship between the flocs growth process and aluminum species.This figure shows formation, breakage and re-formation of HA flocs in different aluminum coagulants treatment. AlCl3 yielded the largest flocs and have better ability to resist shear.
Keywords: Al species; Humic acid; Size; Floc strength; Fractal dimension;

Simulation of the heteroagglomeration between highly size-asymmetric ceramic particles by M. Cerbelaud; A. Videcoq; P. Abélard; R. Ferrando (360-365).
Aggregation phenomena of dilute suspensions composed of two kinds of oxide particles (alumina d 1 = 400   nm and silica d 2 = 25   nm ) have been studied by computer simulations. These particles are oppositely charged and so are prone to heteroagglomerate. The interaction between particles has been modeled by the DLVO potential. Two kinds of simulations have been performed: Brownian dynamics simulations to study the aggregation kinetics and global minimization searches that permit the examination of the most stable configurations of agglomerates. We demonstrate that aggregation should occur also for quite large fractions of added silica (even when 200 silica particles are adsorbed on each alumina particle) and that aggregates are likely to present chainlike shapes. Both findings are in agreement with experiments.Modeling of the aggregation process in a two-components system: (a) dispersed particles, (b) silica nanoparticles adsorption on alumina submicrometer particles, (c) aggregation of silica-covered alumina particles.
Keywords: Dilute colloidal suspensions; Heteroaggregation; Brownian dynamics; Global minimization; Simulation;

Ternary AOT/water/hexane systems as “micellar sieves” for cyanine dye J-aggregates by L.M. Nikolenko; A.V. Ivanchihina; S.B. Brichkin; V.F. Razumov (366-372).
We investigate the behavior of J-aggregates of a cyanine dye, 3 , 3 ′ -di-(γ-sulfopropyl)- 4 , 5 , 4 ′ , 5 ′ -dibenzo-9-ethylthiacarbocyanine betaine pyridinium salt, in AOT/water/hexane reverse micelles ( W = 2 – 50 ), both during the course of rapid microemulsion formation and then after stabilization of the microemulsions at thermodynamic equilibrium. We suggest a new mechanism for J-aggregate formation in reverse micelle solutions. According to this model J-aggregates are formed in the aqueous phase prior to formation of a stable microemulsion, rather than in the process of intermicellar exchange. Reverse micelles encapsulate only those J-aggregates whose size is smaller than the mean size of the water pool. Larger J-aggregates located in hexane gradually precipitate from solution. It is demonstrated that micellar solutions can be used as “sieves” for selection and stabilization of J-aggregates with a desired size.Reverse micelle solutions can be used as “sieves” for selection and stabilization of J-aggregates with a desired size: micelles encapsulate J-aggregates whose size is smaller than the water pool size.
Keywords: J-aggregate; Cyanine dye; Aggregation; Reverse micelle; Surfactant; AOT; w/o microemulsion;

The translational diffusion of Au (gold) ions and Au particles during the photoreduction process from AuCl 4 to metallic Au particles in aqueous ethanol solutions containing poly(N-vinyl-2-pyrrolidone) was investigated by using UV–vis absorption and the laser-induced transient grating (TG) methods. The TG signal of AuCl 4 solution before photoirradiation was composed of three contributions; the thermal grating, the species grating due to the creation of AuCl 2, and that due to the depletion of AuCl 4. Upon photoirradiation, the species grating signal due to AuCl 4 diminished rapidly and the TG signal due to Au particles appeared within a few minutes and became stronger at a very short time. The subsequent reduction of AuCl 2 was concomitant with the formation of Au metal particles. The rapid growth of Au0 atoms into Au particles took place in the short-duration photoirradiation. With the increase of the photoirradiation time, the TG signal was composed of two kinds of Au particle fragments possessing different diffusion coefficients. This is probably due to the pulse-laser induced fragmentation of the larger Au particles. Effects of the polymer on the particle formation were investigated by the concentration dependence of the polymer in the solution. The formation of Au particles by the photoreduction was also compared with that of Pt particles.Time dependence of the TG signal ( I TG ) in water/ethanol (1/1) solutions with PVP observed (a) before and (b to d) after the photoirradiation of AuCl 4, and the schematic illustration of the photoreduction process of the AuCl 4-containing solution.
Keywords: Colloidal dispersions; Gold ions; Gold particles; Photoreduction; Laser induced transient grating method;

Adsorption and onset of lubrication by a double-chained cationic surfactant on silica surfaces by Laurence Serreau; Muriel Beauvais; Caroline Heitz; Etienne Barthel (382-388).
In the lubrication of silica surfaces by double-chained cationic surfactants in aqueous dispersions, there is no direct correlation between friction coefficient and surface excess. Lubrication is primarily controled by the healing of the bilayer defects. Healing is assisted by shear and by high ionic strength.In the context of glass fiber manufacture, the onset of lubrication by a C18 double-chained cationic surfactant has been investigated at high normal contact pressures. Comparison with adsorption kinetics demonstrates that lubrication is not directly connected to the surfactant surface excess but originates from the transition to a defect-free bilayer that generates limited dissipation. The impact of ionic strength and shear rate has also been studied.
Keywords: Friction; Lubrication; Silica; Glass; Surfactant; Surface modification;

The core–shell type Fe3O4 nanoparticles in poly(organosilsesquioxane) (Fe3O4@OcTS) were prepared by one-pot synthesis using reverse micelle method. The as-prepared ferrofluid droplets with average size 4–15 nm were in situ encapsulated via polycondensation of molecularly self-assembled octenyltrimethoxysilane (OcTS). The dynamic light scattering and transmission electron microscopy investigations on coated magnetite nanoparticles revealed uniform size of spherical shape and having thin and transparent shells. These nanoparticles showed redispersibility in non-polar solvents without agglomerations due to coated by a layer of hydrophobic shells. The thermogravimetric analysis and infrared spectroscopy suggested the existence of core–shell type. X-ray diffraction confirmed magnetite cores. The superconducting quantum interference device (SQUID) showed that they exhibited superparamagnetic behavior at 300 K and ferromagnetic at 3 K.
Keywords: Magnetite; Poly(organosilsesquioxane); Surfactant; Reverse micelles; Core–shell type; Redispersibility; Superparamagnetic; Ferromagnetic; Blocking temperature;

Influence of colloidal interactions on pigment coating layer structure formation by Anders Sand; Martti Toivakka; Tuomo Hjelt (394-401).
Consolidation of pigment coating layers was simulated using a particle dynamics model. The effect of various colloidal interaction parameter settings on structure formation and layer thickness was investigated.The consolidation of pigment coating layers was simulated using a three-dimensional particle dynamics model. The model included hydrodynamic interactions as well as colloidal force models and the Brownian motion. The impact of various colloidal model parameters on the z-direction solids profile development and coating layer thickness was investigated. Also, the influence of continuous (liquid) phase viscosity was tested. Particle systems resembling a polydisperse ground calcium carbonate (GCC) distribution were studied. Results show that a lower particle surface potential on pigments increased the thickness of the coating layer, while the electrostatic double layer thickness influenced the internal coating structure. An increased viscosity of the continuous phase slowed the consolidation down, but did not have a significant impact on the final microstructure. The work contributes to the understanding of the influence of colloidal system properties on the consolidation and structure development of coating layers. The results may aid in the understanding of the impact of chemical additives on coating layer structure formation.
Keywords: Pigment coating; Suspension; Colloidal interactions; DLVO; Consolidation; Dynamics; Solids structure;

Preparation of silica stabilized Tobacco mosaic virus templates for the production of metal and layered nanoparticles by Elizabeth S. Royston; Adam D. Brown; Michael T. Harris; James N. Culver (402-407).
Polymerized aniline on TMV allows for thick silica shells to be grown on the surface of the virus. These templates are the foundation for tailorable metalized rod shaped particles.The use of biological molecules as templates for the production of metal nanoparticles and wires is often limited by the stability of the bio-template and its affinity for nucleating metal deposition. In this study, Tobacco mosaic virus (TMV) was used as a model bio-template to investigate the use of silica coatings as a means to both enhance template stability and increase its affinity for metal ions. Results indicate that the unmodified TMV particle can function as a template for the growth of thin (<1 nm) silica layers. However, this thin silica shell did not enhance the stability of the template during metal deposition. To increase silica growth on the TMV template, a pretreatment with aniline was used to produce a uniform silica attractive surface. Aniline pretreated templates yielded significant silica layers of >20 nm in thickness. These silica shells conferred a high degree of stability to the TMV particle and promoted the deposition of various metal nanoparticles through conventional silica mineralization chemistries. This process provides a simple and robust method for the layering of inorganics onto a biological template.
Keywords: Tobacco mosaic virus; Silica; Bio-template; Multilayer; Metalization;

Surface functionalization of germanium ATR devices for use in FTIR-biosensors by Sabrina Devouge; Joséphine Conti; Andréa Goldsztein; Emmanuel Gosselin; Alain Brans; Michel Voué; Joël De Coninck; Fabrice Homblé; Erik Goormaghtigh; Jacqueline Marchand-Brynaert (408-415).
Biosensors based on intrinsic detection methods have attracted growing interest. The use of Fourier transform infra-red (FTIR) spectroscopy with the attenuated internal total reflection (ATR) mode, in the biodetection context, requires appropriate surface functionalization of the ATR optical element. Here, we report the direct grafting of a thin organic layer (about 20 Å depth) on the surface of a germanium crystal. This covering, constructed with novel amphiphilic molecules 2b (namely, 2,5,8,11,14,17,20-heptaoxadocosan-22-yl-3-(triethoxysilyl) propylcarbamate), is stable for several hours under phosphate buffered saline (PBS) flux and features protein-repulsive properties. Photografting of molecule 5 (namely, O-succinimidyl 4-(p-azidophenyl)butanoate) affords the activated ATR element, ready for the covalent fixation of receptors, penicillin recognizing proteins BlaR-CTD for instance. The different steps of the previous construction have been monitored by water contact angle ( θ w ) measurements, spectroscopic ellipsometry (covering depth), X-ray photoelectron spectroscopy (XPS) by using a fluorinated tag for the control of surface reactivity, and FTIR-ATR spectroscopy for the structural analysis of grafted molecules. Indeed, contrarily to silicon device, germanium device offers a broad spectral window (1000–4000 cm−1) and thus amide I and II absorption bands can be recorded. This work lays the foundations for the construction of novel FTIR biosensors.The surface of a germanium ATR crystal was functionalized by a thin, non-fouling, organic covering stable in PBS medium. Protein receptors were grafted by a selective and versatile photochemical method.
Keywords: Germanium; ATR crystal; FTIR biosensors; Thin film; Phenyl azide; Photografting; BlaR-CTD protein; Non-fouling surface;

NiAg catalysts prepared by reduction of Ni2+ ions in aqueous hydrazine by M.M. Bettahar; R. Wojcieszak; S. Monteverdi (416-424).
A series of bimetallic NiAg (Ni + Ag = 1% wt) catalysts supported on amorphous silica was synthesized via chemical reduction using hydrazine as the reducing agent at 353 K. Catalysts were prepared via impregnation or precipitation technique. It was found that the reduction of the Ni2+ ions occurred only in the presence of silver, otherwise a stable blue [Ni(N2H4)3]2+ complex was formed. Comparisons with similar NiAg catalysts supported on crystallized silica as prepared in our previous work indicated that the Ni2+ ions weakly interacted with acidic crystallized silica on which they were readily reduced. For both supports, the combination of silver and nickel gave rise to a synergistic effect due to the existence of NiAg groupings. The surface and catalytic properties of the metal particles formed depended on the Ni:Ag ratio, method of preparation, and acidity of the support.We studied amorphous silica-supported NiAg catalysts prepared by the hydrazine method. We found that silver permitted hydrazine reduction of the strongly bonded supported Ni2+ ions and, more strikingly, sharply enhanced metal dispersion and catalytic activity of nickel. The results suggest the existence of NiAg species in connection with metal reduction mechanisms and support acid–base properties.
Keywords: Supported bimetallic catalysts; Nickel; Silver; Silica; Hydrazine; Benzene hydrogenation;

Synthesis of sphere nanostructured MoS2 is reported. Characterization of the synthesized MoS2 was investigated by X-ray diffraction, nitrogen adsorption, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It was found that the obtained MoS2 is composed of layers that bend to form mostly spheres, with an average diameter of ∼180 nm. The growth in crystallinity is mainly due to the increased number of the round-stacked layers of MoS2. The catalytic activity and selectivity of the synthesized nanostructured MoS2 for the dibenzothiophene hydrodesulfurization were investigated. The closed-circle MoS2 layers exhibited a high selectivity for the direct sulfur removal.Quasispherical nanosized MoS2 was synthesized from the thermal treatment of ammonium heptamolybdate tetrahydrate precursor. The obtained structure consisted mostly of closed-circle MoS2 layers. This MoS2 structure performed the hydrodesulfurization of dibenzothiophene preferentially via the direct C–S bond cleavage route.
Keywords: MoS2; MoO2; Bent layers; Hydrodesulfurization;

Four synthetic protocols have been examined for the preparation of a self-assembled monolayer of propanethiol functions on glass surfaces, through the wet reaction of mercaptopropyltrimethoxysilane (MPTS) on glass slides, in order to determine an optimal method to obtain dense ―SH monolayers for further reaction with maleimide-bearing molecules. We have also demonstrated that the surface density of reactive ―SH groups can be indagated by the coupling reaction with a maleimide-functionalized rhodamine dye and by the examination of the absorption spectra of the glass slides. The reaction of MPTS in dry toluene gives the most dense surface of reactive thiols, among the examined protocols. We have also evidenced that thermal curing of the MPTS functionalized slides induces thiol coupling and ―S―S― formation, resulting in a dramatically lowered availability of ―SH groups.The ability of different synthetic protocols to produce MPTS monolayers on glass available for further ―SH/maleimide reaction is examined by coupling the thiols with a maleimide-functionalized dye.
Keywords: Self-assembled monolayers; Surface chemistry; Glass; Maleimide–thiol coupling; UV–Vis spectroscopy; FTIR ATR spectroscopy;

Preparation of a hydroxyapatite film and its application in the removal and regeneration of aqueous cations by Shigeru Sugiyama; Yuka Shimizu; Tomoyuki Manabe; Keizo Nakagawa; Ken-Ichiro Sotowa (439-443).
Aqueous Pb2+, Cd2+, Co2+, and Cu2+ were continuously removed and regenerated using a powder of calcium hydroxyapatite (CaHAp) and a glass plate coated with a thin film of CaHAp.Aqueous Pb2+, Cd2+, Co2+, and Cu2+ were continuously removed and regenerated using a bulk powder of calcium hydroxyapatite (Ca10(PO4)6(OH)2, CaHAp) and a glass plate coated with a thin film of CaHAp. Although use of CaHAp effectively removed aqueous Pb2+ from the wastewater, lead cations immobilized on CaHAp could not be regenerated in an aqueous solution due to the formation of lead hydroxyapatite (Pb10(PO4)6(OH)2), which is insoluble in water at acidic and neutral pH. In contrast, Co2+ and Cu2+ immobilized on CaHAp were easily regenerated in an aqueous solution by treatment with an acidic aqueous solution containing Ca(NO3)2, as previously reported for the CaHAp-Cd2+ system. We found that the combination of the removal of the aqueous divalent cations by the CaHAp film and subsequent regeneration of the immobilized divalent cations from the film allowed for recycling of the film and for removal and regeneration of aqueous Cd2+, Co2+, and Cu2+.
Keywords: Calcium hydroxyapatite; Removal and regeneration; Aqueous divalent cations;

Ni-MFI zeolites with high percentage of Ni (5–15 wt%) were prepared by using an ionic complex [(C4H9)4N]+ 2[Ni(EDTA)]2− by one step synthesis. These molecular sieves were characterized using X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), Fourier-transform infrared spectroscopy (FT-IR), ultraviolet–visible spectroscopy (UV–vis), differential scanning calorimeter (DSC) and nitrogen adsorption–desorption isotherms. The results showed that heteroatom Ni was successfully introduced into the MFI framework up to 15 wt%. Moreover, this Ni-MFI possessed regular and stable structure with high specific surface area and average pore diameter of 388–439 m2 g−1 and 2.566–3.828 nm, respectively, compared to MFI prepared by traditional methods. These samples also showed good thermal and hydrothermal stability.Schematic of the synthetic mechanism of new template [(C4H9)4N]+ 2[Ni(EDTA)]2− for synthesizing the mesoporous zeolite Ni-MFI.
Keywords: Ni-MFI; Mesoporous materials; Ionic complex; Molecular sieve; Synthesis;

Marangoni flow revisited by Rafael Tadmor (451-454).
A view of the Marangoni effect from the perspectives of all three possible interfaces as motion inducing agents is given. Arguments are made that it is required and sufficient that surface tension gradient at the substrate surface induce the flow while the liquid vapor surface tension gradient is unable to induce a flow on its own; that the flow is toward a lower interface potential at the wall liquid interface; and that this is an appropriate way of viewing the Marangoni effect is demonstrated with examples.Tears of wine flow along the modified solid surface potential.
Keywords: Marangoni flow; Tears of wine; Interfacial potential;

Chasing drops: Following escaper and pursuer drop couple system by Prashant Bahadur; Preeti S. Yadav; Kumud Chaurasia; Aisha Leh; Rafael Tadmor (455-460).
We study experimentally six different systems in which Marangoni flow is induced by two chemically different drops on a solid surface in air. In such systems one drop seems to chase away the other. We show that in all the systems studied, the Marangoni flow is induced at the solid–vapor interface as opposed to the air–liquid interface. This is true even for the case of water drop and alcohol drop on a glass surface (which corresponds to the “tears of wine” classical case). Thus we explain the drop motion as a result of an interfacial tension gradient which takes place primarily at the air–surface region and less, if at all, at the two other interfaces in the problem: the liquid–substrate or liquid–air interfaces. Then we follow the motion of drops on surfaces and find that it is discontinuous, i.e. characterized by stops and jumps as in a stick slip mechanism. We explain this behavior by an increase in the Laplace pressure that creates a higher anchoring pinning effect at the front edge of the moving drop. The understanding of this process has implications for passively separating mixed liquids.The Marangoni flow is a surface driven phenomenon rather than liquid–air driven.
Keywords: Marangoni flow; Drop couples;

To investigate the effect of fluorination on the surface of polydimethylsiloxane (PDMS) film, direct fluorination was performed under a mild condition (approx. 2000 μmol/mol F2 in nitrogen) for 120 min. No structural damage of PDMS films was observed on the scanning electron microscopic images under the condition. Fourier-transform infrared/attenuated total reflectance (FTIR/ATR) and energy dispersive X-ray spectroscopy (EDS) results showed a successful fluorine introduction resulting in the structural change of PDMS. Surface property changes of PDMS films with respect to the extent of direct fluorination were also examined. Contact angles of water and alcohols on the PDMS surfaces decreased as fluorination time increased. Most alcohols showed greater decrease than water in the contact angle as a result of long-term fluorination, which sometimes results in zero contact angles of alcohols on the PDMS surfaces. Surface energy of PDMS films increased more than 200% after the direct fluorination for 120 min.Direct fluorination resulted in a successful formation of fluorine-containing polydimethylsiloxane surfaces without defects. They showed greater affinity to polar and mid-polar alcohols than water and 1-octanol.
Keywords: Polydimethylsiloxane; Surface modification; Direct fluorination; Surface energy; Contact angle;

In this paper, we studied the role of vertical component of surface tension of a water droplet on the deformation of membranes and microcantilevers (MCLs) widely used in lab-on-a-chip and micro- and nano-electromechanical system (MEMS/NEMS). Firstly, a membrane made of a rubber-like material, poly(dimethylsiloxane) (PDMS), was considered. The deformation was investigated using the Mooney–Rivlin (MR) model and the linear elastic constitutive relation, respectively. By comparison between the numerical solutions with two different models, we found that the simple linear elastic model is accurate enough to describe such kind of problem, which would be quite convenient for engineering applications. Furthermore, based on small-deflection beam theory, the effect of a liquid droplet on the deflection of a MCL was also studied. The free-end deflection of the MCL was investigated by considering different cases like a cylindrical droplet, a spherical droplet centered on the MCL and a spherical droplet arbitrarily positioned on the MCL. Numerical simulations demonstrated that the deflection might not be neglected, and showed good agreement with our theoretical analyses.Besides bending, a local twisting of the microcantilever was also found. The twisting was induced by the eccentricity of the microdrop.
Keywords: Mooney–Rivlin constitutive model; Hyperelastic material; PDMS; Membrane; Surface tension; Vertical component; Water droplet; Microcantilever;

Stability and interface properties of thin cellulose ester films adsorbed from acetone and ethyl acetate solutions by Jorge Amim; Priscila M. Kosaka; Denise F.S. Petri; Francisco C.B. Maia; Paulo B. Miranda (477-483).
Stability and interface properties of cellulose acetate propionate (CAP) and cellulose acetate butyrate (CAB) films adsorbed from acetone or ethyl acetate onto Si wafers have been investigated by means of contact angle measurements and atomic force microscopy (AFM). Surface energy ( γ S total ) values determined for CAP adsorbed from acetone are larger than those from ethyl acetate. In the case of CAB films adsorbed from ethyl acetate and acetone were similar. Dewetting was observed by AFM only for CAP films prepared from ethyl acetate. Positive values of effective Hamaker constant ( A eff ) were found only for CAP prepared from ethyl acetate, corroborating with dewetting phenomena observed by AFM. On the contrary, negative values of A eff were determined for CAP and CAB prepared from acetone and for CAB prepared from ethyl acetate, corroborating with experimental observations. Sum frequency generation (SFG) vibrational spectra indicated that CAP and CAB films prepared from ethyl acetate present more alkyl groups oriented perpendicularly to the polymer–air interface than those films prepared from acetone. Such preferential orientation corroborates with macroscopic contact angle measurements. Moreover, SFG spectra showed that acetone binds strongly to Si wafers, creating a new surface for CAP and CAB films.The present work has shown that acetone (a) binds strongly to SiO2 surfaces, creating a new surface for cellulose ester deposition and avoiding dewetting. On the contrary, ethyl acetate (b) was able to induce perpendicular orientation of polymer alkyl groups to the surface, leading to hydrophobic surfaces.
Keywords: Cellulose ester; Films; Dewetting; Atomic force microscopy; Sum frequency generation;

Preparation of MTMS based transparent superhydrophobic silica films by sol–gel method by A. Venkateswara Rao; Sanjay S. Latthe; Digambar Y. Nadargi; H. Hirashima; V. Ganesan (484-490).
Figure shows when the TMCS (A) and HMDZ (B) modified films were cured at temperatures higher than 350 °C and 335 °C, respectively, the films became superhydrophilic.Superhydrophobic surfaces with water contact angle higher than 150° generated a lot of interest both in academia and in industry because of the self-cleaning properties. Optically transparent superhydrophobic silica films were synthesized at room temperature (27 °C) using sol–gel process by a simple dip coating technique. The molar ratio of MTMS:MeOH:H2O (5 M NH4OH) was kept constant at 1:10.56:4.16, respectively. Emphasis is given to the effect of the surface modifying agents on the hydrophobic behavior of the films. Methyl groups were introduced in the silica film by post-synthesis grafting from two solutions using trimethylchlorosilane (TMCS) and hexamethyldisilazane (HMDZ) silylating agents in hexane solvent, individually. The percentage of silylating agents and silylation period was varied from 2.5 to 7.5% and 1 to 3 h, respectively. The TMCS modified films exhibited a very high water contact angle ( 166 ± 2 ° ) in comparison to the HMDZ ( 138 ± 2 ° ) modified films, indicating the water repellent behavior of the surface. When the TMCS and HMDZ modified films were heated at temperatures higher than 350 °C and 335 °C, respectively, the films became superhydrophilic; the contact angle for water on the films was smaller than 5°. Further, the humidity study was carried out at a relative humidity of 85% at 30 °C temperature over 30 days. The films have been characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FT-IR), % optical transmission, humidity tests and contact angle (CA) measurements.
Keywords: Sol–gel process; Superhydrophobic surfaces; Hydrophobicity; Wetting phenomena; Transparent; Humidity; Stability; Coatings;

We model an aqueous system which comprises a mixture of lipid molecules and hydrophobic nanoparticles, by means of a self-consistent mean-field theory (SCMFT). Lipids are modeled as nonlinear/branched copolymers with a single hydrophilic head group and a double hydrophobic tail, whereas nanoparticles are modeled as hard-spheres of a particular size. The mixture of lipids and nanoparticles leads to a formation of core–shell micellar structures where the hydrophobic nanoparticles and lipid tails form the core of the micelle, and the hydrophilic lipid head groups form the shell. Different micellar morphologies are found depending on the total concentration of lipid molecules and nanoparticles, as well as the relative size of nanoparticles. There exist three distinct equilibrium morphologies of lipid–nanoparticle micelles: circular micelles (CM), ellipsoidal micelles (EM), and bilayer/lamellar structures (BL). We observed some smooth morphological transitions and phase coexistences by evaluating the excess free energy of micelles.Micellar structures of lipid–nanoparticle mixtures in aqueous solvent are modeled by using SCMFT.
Keywords: Lipid–nanoparticle; Micelles; Equilibrium morphology;

On the effect of pH on spreading of surfactant solutions on hydrophobic surfaces by Jovana Radulovic; Khellil Sefiane; Martin E.R. Shanahan (497-504).
Surfactants are invaluable in a number of agricultural applications in products such as pesticides and herbicides. In these products, surfactants are very often used in conjunction with acidifiers in order to improve their half-life. In this paper, we investigate how the change in pH affects surfactant wetting and spreading. We compare the performance of a conventional surfactant, Triton® X-100, with that of a trisiloxane superspreader, Silwet® L-77, on a number of polymer coated surfaces exhibiting various degrees of hydrophobicity. Silwet® L-77 in water based solutions showed very good wetting capability on all surfaces. However, its wetting ability was drastically reduced with the addition of acetic acid. On the other hand, Triton® X-100 was not affected by the addition of acid and exhibited the same spreading behaviour as in water-based solutions.Differences in molecular structures of the alkyl polyethoxylates and trisiloxane surfactants, like hydrophobic head's geometry, are most likely the reason of superspreaders' supremacy over conventional surfactants.
Keywords: Hydrophobicity; pH; Superspreader; Surfactant; Wetting;

Dendrimer-encapsulated Pt nanoparticles in supercritical medium: Synthesis, characterization, and application to device fabrication by Sreenivasa Reddy Puniredd; Chan Mei Yin; Yeong Sai Hooi; P.S. Lee; M.P. Srinivasan (505-510).
In this work we describe a general method for formation of Pt nanoparticles within an ultrathin film matrix and its application for non-volatile memory (NVM). Our approach involves the formation of Pt nanoparticles within ultrathin film matrix formed by covalent layer-by-layer (LbL) assembly of pyromellitic dianhydride (PMDA) and second generation of polyamidoamine (PAMAM) dendrimer in supercritical carbon dioxide (SCCO2). The hyperbranched component in the film structure serves to confine nanoparticle size and improve distribution. The memory effect and retention capability is demonstrated by means of a metal-insulator semiconductor (MIS) device fabricated using the nanoparticle-laden thin film as the insulating layer.High-frequency (1 MHz) C – V characteristics of the MIS devices with and without Pt nanoparticles in immobilized dendrimer layer.
Keywords: Pt nanoparticles; Supercritical carbon dioxide; Dendrimer; Covalent molecular assembly of ultrathin films and MIS device;

Effect of buffers on aqueous solute-exclusion zones around ion-exchange resins by Jian-ming Zheng; Adam Wexler; Gerald H. Pollack (511-514).
Charged latex particles in buffer solutions are uniformly excluded from several-hundred-micron-thick shells surrounding ion-exchange beads regardless of charge sign polarity.Interaction between charged surfaces in aqueous solution is a fundamental feature of colloid science. Theoretically, surface potential falls to half its value at a distance equal to a Debye length, which is typically on the order of tens to hundreds of nanometers. This potential prevents colloids from aggregating. On the other hand, long-range surface effects have been frequently reported. Here we report additional long-range effects. We find that charged latex particles in buffer solutions are uniformly excluded from several-hundred-micron-thick shells surrounding ion-exchange beads. Exclusion is observed whether the beads are charged similarly or oppositely to the particles. Hence, electrostatic interactions between bead and microsphere do not cause particle exclusion. Rather, exclusion may be the consequence of water molecules re-orienting to produce a more ordered structure, which then excludes the particles.
Keywords: Buffers; Colloids; Ion exchange; Exclusion zones; Water;

A new equation is derived from a combination of the BET (Brunauer, Emmett, Teller) and Freundlich isotherms fitted for liquid phase adsorption data on activated carbons. This equation, depending on the Freundlich parameters and the equilibrium adsorption–desorption constant can be used for assessment of the surface area occupied by the solute molecules on a surface in a liquid phase system under some conditions.At low concentration the isotherm data is closer to the BET fit, then closer to the Freundlich one. An equation is derived from a combination of the BET and Freundlich isotherms.
Keywords: Liquid phase adsorption; Freundlich isotherm; Surface area; BET isotherm;