Journal of Colloid And Interface Science (v.308, #1)

Comment on “Two touching spherical drops in uniaxial extensional flow: Analytic solution to the creeping flow problem” by M.B. Nemer; X. Chen; D.H. Papadopoulos; J. Bławzdziewicz; M. Loewenberg (1-3).
From an analysis of tangent spherical drops in straining flow, Baldessari and Leal conclude that the drop-scale internal circulation, driven by the ambient flow, has a negligible influence on the drainage of the thin liquid film between drops under small-deformation conditions [F. Baldessari, L.G. Leal, J. Colloid Interface Sci. 289 (2005) 262]. However, their conclusion is incorrect as explained in this letter.
Keywords: Drop coalescence; Film drainage; Noncoalescence; Stokes flows;

Fluoroalkanoyl peroxide reacted with 1,3,5,7-tetravinyl-1,3,5,7-tetramethylcyclotetrasiloxane (TTRV-Si) to afford fluoroalkyl end-capped oligomers containing some unreacted vinyl segments under very mild conditions. Fluoroalkyl end-capped cyclosiloxane oligomers containing some vinyl segments thus obtained reacted with N , N -dimethylacrylamide and fluoroalkanoyl peroxide to afford new fluorinated dendrimer-type block copolymers in good isolated yield. Similar reactions were also occurred by the use of 1,3,5-trivinyl-1,3,5-trimethylcyclotrisiloxane instead of TTRV-Si, and the corresponding fluorinated dendrimer-type block copolymer was obtained in good isolated yield. These fluorinated dendrimer-type block copolymers had an excellent solubility not only in water but also in traditional organic solvents including aliphatic fluorinated solvents. Interestingly, these fluorinated block copolymers were found to form the self-assembled dendrimer-type polymeric aggregates in aqueous solutions. More interestingly, these fluorinated block copolymers had an extremely higher dispersion ability of not only single-walled carbon nanotube and fullerenes but also magnetic nanoparticles into water, compared to that of the corresponding two fluoroalkyl end-capped oligomers.Fluorinated dendrimer-type block copolymers [RF-(TTRV-Si) n -RF-block-RF-(DMAA) q -RF] exhibited an extremely higher dispersion ability for not only single-walled carbon nanotube and fullerenes but also magnetic nanoparticles into water.
Keywords: Dendrimer-type copolymer; Fluorinated copolymer; Fluoroalkanoyl peroxide; Vinylsilanes; Molecular aggregate; Dispersion; Carbon nanotubes; Fullerenes; Magnetites;

Effect of lead on the sorption of phenol onto montmorillonites and organo-montmorillonites by Liang-guo Yan; Xiao-quan Shan; Bei Wen; Shuzhen Zhang (11-19).
The effect of lead (Pb) on the sorption of phenol onto montmorillonite-based sorbents was studied using a batch equilibration method when phenol and Pb were sorbed simultaneously and either Pb or phenol was previously sorbed. The sorbents were Na+-, Ca2+-, hexadecyl trimethylammonium (HDTMA)-Na+-, and HDTMA-Ca2+-montmorillonites. Pb diminished the sorption of phenol largely onto Na+- or Ca2+-montmorillonites, while phenol had little effect on the sorption of Pb onto all sorbents. Pb had no effect on the sorption of phenol onto HDTMA-Na+- or HDTMA-Ca2+-montmorillonites either. The sorption capacity of phenol followed the order HDTMA-Na+- > HDTMA-Ca2+- > Na+- > Ca2+-montmorillonites. The pseudo-second-order equation described the kinetics of phenol sorption well. Sorption isotherms of phenol followed the Freundlich equation. Phenol sorption on HDTMA-Na+- and HDTMA-Ca2+-montmorillonites was linear, while that on Na+- and Ca2+-montmorillonites was nonlinear.Effect of Pb on the sorption of phenol was evaluated. For Na+- and Ca2+-montmorillonites the sorption of phenol decreased clearly when Pb was added simultaneously. In contrast, Pb had insignificant effect on the sorption of phenol on HDTMA-Na+- and HDTMA-Ca2+-montmorillonites.
Keywords: Na+-; Sorption; Sorption kinetics; Phenol; Pb;

Dynamic particle adhesion from flow over collecting surfaces with nanoscale heterogeneity occurs in important natural systems and current technologies. Accurate modeling and prediction of the dynamics of particles interacting with such surfaces will facilitate their use in applications for sensing, separating, and sorting colloidal-scale objects. In this paper, the interaction of micrometer-scale particles with electrostatically heterogeneous surfaces is analyzed. The deposited polymeric patches that provide the charge heterogeneity in experiments are modeled as 11-nm disks randomly distributed on a planar surface. A novel technique based on surface discretization is introduced to facilitate computation of the colloidal interactions between a particle and the heterogeneous surface based on expressions for parallel plates. Combining these interactions with hydrodynamic forces and torques on a particle in a low Reynolds number shear flow allows particle dynamics to be computed for varying net surface coverage. Spatial fluctuations in the local surface density of the deposited patches are shown responsible for the dynamic adhesion phenomena observed experimentally, including particle capture on a net-repulsive surface.Particle dynamics are studied in shear flow over surfaces with charge heterogeneity at the 10-nm scale using a novel technique to evaluate the electrostatic double layer interactions.
Keywords: Particle deposition; Charge heterogeneity; Nanotextured surface; Colloidal interaction; DLVO; Electrostatic double layer; Sphere–flat plate; Derjaguin approximation; Patchy surface; Patch model;

Chemisorption of carbon dioxide on potassium-carbonate-promoted hydrotalcite by K.B. Lee; A. Verdooren; H.S. Caram; S. Sircar (30-39).
New equilibrium and column dynamic data for chemisorption of carbon dioxide from inert nitrogen at 400 and 520 °C were measured on a sample of potassium-carbonate-promoted hydrotalcite, which was a reversible chemisorbent for CO2. The equilibrium chemisorption isotherms were Langmuirian in the low-pressure region ( p CO 2 < 0.2   atm ) with a large gas–solid interaction parameter. The isotherms deviated from Langmuirian behavior in the higher pressure region. A new analytical model that simultaneously accounted for Langmuirian chemisorption of CO2 on the adsorbent surface and additional reaction between the gaseous and sorbed CO2 molecules was proposed to describe the measured equilibrium data. The model was also capable of describing the unique loading dependence of the isosteric heat of chemisorption of CO2 reported in the literature. The column breakthrough curves for CO2 sorption from inert N2 on the chemisorbent could be described by the linear driving force (LDF) model in conjunction with the new sorption isotherm. The CO2 mass-transfer coefficients were (i) independent of feed gas CO2 concentration in the range of the data at a given temperature and (ii) a weak function of temperature. The ratio of the mass-transfer zone length to the column length was very low due to highly favorable CO2 sorption equilibrium.The chemisorption isotherm of CO2 on K2CO3-promoted hydrotalcite at 400 °C can be described by the Langmuir model only in the low-pressure region. A novel chemisorption–surface reaction model is developed to describe the isotherm in the high-pressure region.
Keywords: Chemisorption; Equilibrium; Kinetics; Carbon dioxide; Promoted hydrotalcite; Model isotherm;

Proton interaction in phosphate adsorption onto goethite by Bin Zhong; Robert Stanforth; Shunnian Wu; J. Paul Chen (40-48).
The adsorption of phosphate on goethite is generally modeled by assuming a simple ligand exchange reaction with surface hydroxyl groups. This study investigates the binding forms of phosphate on goethite by evaluating the proton interaction and surface charge change during phosphate adsorption. It is found that OH release stoichiometry increases with phosphate coverage, which suggests that different mechanisms predominate at different phosphate loadings. It demonstrates that surface binding changes from monodentate complexation to bidentate complexation with increasing surface phosphate coverage. The net OH release accompanying this transformation is best interpreted with a 2 p K a multisite model.Comparison of measured slope k value with theoretical surface charge change in multisite model.
Keywords: Phosphate; Goethite; Adsorption; OH release stoichiometry; Monodentate complex; Bidentate complex;

A common computational method for the characterization of porous materials is to calculate the adsorption isotherm of fluids in the materials from the preassumed wall–fluid potential. If the wall–fluid potential is unknown, the common computational method becomes invalid. In a realistic experiment, however, it is common to know the experimental adsorption isotherm of nitrogen and not to know the wall–fluid potential. Here we propose a stepwise approximation for modeling wall–fluid potential under conditions where only the adsorption isotherm of nitrogen is measured experimentally. Based on the modeled wall–fluid potential, we can characterize the porous materials and predict the adsorption of other adsorbates on the materials. It is expected that the approach would provide a powerful means for the characterization of novel materials under conditions where only the experimental adsorption isotherm is available.We propose a stepwise approximation for modeling wall–fluid potential. On the basis of the modeled wall–fluid potential, we can characterize the porous materials and predict adsorption of other adsorbates on the materials.
Keywords: Adsorption; Mesoporous materials; Stepwise approximation; Wall–fluid potential;

Phosphate adsorption on hematite was characterized as a function of pH (3.5–8.9) and phosphate concentration (5–500 μM) by in situ ATR-FTIR spectroscopy. Under most conditions a mixture of different (inner-sphere) phosphate complexes existed at the hematite surface, with the relative importance of these complexes varying with pH and surface coverage. Experiments using D2O and H2O indicated the presence of two protonated phosphate surface complexes at pH/pD = 3.5–7.0. Comparison to spectra of protonated aqueous phosphate species suggested that these surface complexes are monoprotonated. The difference in the IR spectra of these complexes is tentatively interpreted to result from a different surface coordination, with one surface complex coordinated in a monodentate binuclear (bridging) fashion, and the second as a monodentate mononuclear complex. Alternatively, the bridging complex may be a (protonated) monodentate mononuclear complex exhibiting strong hydrogen bonding to an adjacent surface site, and the second species a monodentate complex exhibiting limited hydrogen bonding. Formation of the bridging complex is favored at lower pH values and higher surface loadings in the 3.5–7.0 pH range. At the highest pH values studied (8.5–9.0) a third complex, interpreted to be a nonprotonated monodentate mononuclear complex, is present along with the monodentate monoprotonated surface species. The importance of the nonprotonated monodentate complex increases with increasing surface coverage at these high pH values.
Keywords: Adsorption; ATR-FTIR spectroscopy; Phosphate; Hematite; In situ; Speciation; Protonation; Surface complexation;

Formation of protein molecular imprints within Langmuir monolayers: A quartz crystal microbalance study by Nicholas W. Turner; Bryon E. Wright; Vladimir Hlady; David W. Britt (71-80).
Protein imprinting leading to enhanced rebinding of ferritin to ternary lipid monolayers is demonstrated using a quartz crystal microbalance. Monolayers consisting of cationic dioctadecyldimethylammonium bromide, non-ionic methyl stearate, and poly(ethylene glycol) bearing phospholipids were imprinted with ferritin at the air/water interface of a Langmuir–Blodgett trough and transferred hydrated to hydrophobic substrates for study. This immobilization was shown by fluorescence correlation spectroscopy to significantly hinder any further diffusion of lipids, while rebinding studies demonstrated up to a six-fold increase in ferritin adsorption to imprinted versus control monolayers. A diminished rebinding of ferritin to its imprint was observed through pH reduction to below the protein isoelectric point, demonstrating the electrostatic nature of the interaction. Rebinding to films where imprint pockets remained occupied by the template protein was also minimal. Studies with a smaller acidic protein revealed the importance of the steric influence of poly(ethylene glycol) in forming the protein binding pockets, as albumin-imprinted monolayers showed low binding of ferritin, while ferritin-imprinted monolayers readily accommodated albumin. The controllable structure–function relationship and limitations of this system are discussed with respect to the application of protein imprinting in sensor development as well as fundamental studies of proteins at dynamic interfaces.Protein imprinting in Langmuir monolayers.
Keywords: Protein adsorption; Molecular imprinting; Langmuir monolayer; Mixed monolayer; Quartz crystal microbalance; QCM; Fluorescence correlation spectroscopy; FCS; Poly(ethylene glycol); PEG; Ferritin;

Synthesis of nano-sized TiO2/poly(AA-co-MMA) composites by heterocoagulation and blending with PET by Jui-Hung Chen; Chi-An Dai; Hung-Jen Chen; Pei-Chi Chien; Wen-Yen Chiu (81-92).
Nano-sized TiO2 or SiO2/TiO2 particles were prepared by hydrolysis and condensation reactions in aqueous media, followed by mixing with poly(AA-co-MMA) latex to form different composites, then blending with poly(ethylene terephthalate), PET. The TGA results of composites indicated that negative charged latexes had greater interaction with TiO2/ or SiO2/TiO2 particles through strong electrostatic forces, while cationic latexes incorporated with TiO2 or SiO2/TiO2 particles by pH induced coagulation, carbonyl group chelation and hydrogen bonding. The soapless latex polymer particles showed lower ability of adsorption to TiO2 particles due to the decrease of total surface area of these larger particles. If SiO2/TiO2 particles were used instead of TiO2 particles, unexpected high adsorption result was observed. Morphology results observed by SEM showed that PET blended with positive charged composites was more homogeneous than PET blended with negative charged composites. DSC results also indicated that the T g of PET was increased, melting temperatures ( T m or T m ′ ) were increased, and the temperature range of crystallization was narrowed after blending with the composites. The presence of composites affected the mobility and packing of PET molecular chains therefore changing the thermal properties of PET.SEM of TiO2/cationic latex composite (c) showed homogeneous distribution of TiO2, while large aggregations of TiO2 particles were apparent in the SEM of TiO2/soapless latex composite (a). The morphology of TiO2/anionic latex complex (b) showed less aggregation than TiO2/soapless latex composite.
Keywords: TiO2; SiO2; Poly(AA-co-MMA); Composite latexes; PET blends;

We investigate the surface viscoelasticity of β-lactoglobulin and β-casein spread surface monolayers using a recently discovered method. Step compressions are performed, and the surface pressure is measured as a function of time. This is a common experiment for surface monolayers. However in our experiments the pressure is recorded by two perpendicular sensors, parallel and perpendicular to the compression direction. This enables us to clearly measure the time relaxation of both the compression and shear moduli, at the same time, in a single experiment, and with a standard apparatus. β-Lactoglobulin and β-casein monolayers are interesting because of their importance in food science and because they exhibit universally slow dynamical behavior that is still not fully understood. Our results confirm that the compressional modulus dominates the total viscoelastic response in both proteins. Indeed for β-casein we confirm that the shear modulus is always negligible, i.e., the layer is in a fluid state. In β-lactoglobulin a finite shear modulus emerges above a critical concentration. We emphasize that in Langmuir trough dynamic experiments the surface pressure should be measured in both the compression and the perpendicular directions.Anisotropy in the surface pressure shows that β-casein monolayers are in a fluid state, whereas in β-lactoglobulin a finite shear modulus emerges above a critical concentration.
Keywords: Surface monolayer; Interfacial rheology; Stress relaxation; β-Casein; β-Lactoglobulin; Compression; Shear;

We consider the effect of surface tension upon fluctuations within the core of drops and bubbles. We also investigate the fluctuations of the substance density ρ, volume V, and particle number N within the objects under study. It is demonstrated that cores of drops and bubbles are homogeneous when they contain several thousand nanoparticles (molecules, atoms). Fluctuations of particle number are very large within the nucleus core containing only a few nanoparticles. Therefore, the surface tension has a probabilistic character since there is no surface separating the nucleus substance from the surrounding medium, only a transitional zone whose radius fluctuates considerably in time. In this case, it is more correct to consider not the surface tension but a certain quantity that we named the quasi surface tension.The (quasi)surface tension σ of drops, bubbles and their nuclei depending on the radius R of their cores. 1–2 is a transitional zone. The (- - -) marks an area of large fluctuations. N is the particle number.
Keywords: Surface tension; Interface; Fluctuations; Bubbles; Drops;

Size control synthesis of polymer-stabilized water-soluble platinum oxide nanoparticles by Baolin He; Yao Ha; Hanfan Liu; Keming Wang; Kong Yong Liew (105-111).
A series of narrowly distributed nanoparticles with different sizes of platinum oxide stabilized by polyvinylpyrrolidone (PVP) were synthesized by hydrolytic decomposition of platinum chloride. The as-synthesized nanoparticles were characterized by UV–vis, TEM, and XPS examination. Studies on the parameters influencing the size of the as-synthesized platinum oxide nanoparticles were carried out. The pH of the solution was demonstrated to be the main factor affecting the particle diameter. The particles size also decreased with the increasing molar ratio of stabilizer (PVP):PtCl4. The influence of the concentration of sodium acetate on the rate of hydrolytic decomposition and the condensation reaction was studied. It was found that increasing the concentration of sodium acetate increased the rate of the condensation reaction nearly linearly.A way of size-controlling synthesis of polymer-stabilized water-soluble platinum oxide nanoparticles is presented. Factors affecting the rate of the condensation reaction are also studied.
Keywords: Platinum oxide; Nanoparticle; Colloid; Water-soluble; Polyvinylpyrrolidone;

Chemical bath deposition synthesis of sub-micron ZnS-coated polystyrene by Kevin J. Huang; Poorna Rajendran; Chekesha M. Liddell (112-120).
The synthesis of ZnS-coated polystyrene composite colloids by the decomposition of thioacetamide in the presence of polystyrene seed particles and metal salt is presented. The chemical bath deposition technique incorporates poly(vinyl pyrrolidone) to inhibit particle aggregation during the synthesis so that core–shell particles with sizes in the low sub-micron range were achieved. The shell thickness was well controlled through the reaction time and core size. ZnS shells were composed of primary crystallites, approximately 5 nm in diameter, which had the zinc blend crystal structure. The porosity of the shells was between 12 and 19%. Accordingly, the effective refractive index of the particles varied between 1.73 and 1.98 at wavelengths above the optical absorption edge of ZnS. Ordered colloidal crystals were produced by convective assembly of the poly(sodium 4-styrenesulfonate) stabilized core–shell particles. Assemblies of ZnS shell–polystyrene core particles are photonic crystal materials which may have applications in optical computing and communications environments.The chemical bath deposition of ZnS shells with well-controlled thickness onto polystyrene seed particles is reported. The composite particles were stabilized with polyanion and assembled into 3D ordered colloidal crystals.
Keywords: Core–shell; Colloid; Zinc sulfide; Polystyrene; Photonic crystal; Chemical bath deposition;

Encapsulation of emulsion droplets by organo–silica shells by C.I. Zoldesi; P. Steegstra; A. Imhof (121-129).
Surfactant-stabilized emulsion droplets were used as templates for the synthesis of hollow colloidal particles. Monodisperse silicone oil droplets were prepared by hydrolysis and polymerization of dimethyldiethoxysiloxane monomer, in the presence of surfactant: sodium dodecyl sulphate (SDS, anionic) or Triton X-100 (non-ionic). A sharp decrease in the average droplet radius with increasing surfactant concentration was found, with a linear dependence of the droplet radius on the logarithm of the surfactant concentration. The surfactant-stabilized oil droplets were then encapsulated with a solid shell using tetraethoxysilane, and hollow particles were obtained by exchange of the liquid core. The size and polydispersity of the oil droplets and the thickness of the shell were determined using static light scattering, and hollow particles were characterized by electron microscopy. Details on the composition of the shell material were obtained from energy-dispersive X-ray analysis. In the case of sodium dodecyl sulphate, the resulting shells were relatively thin and rough, while when Triton X-100 was used, smooth shells were obtained which could be varied in thickness from very thick (≈150 nm) to very thin shells (≈17 nm). Finally, hexane droplets were encapsulated using the same procedure, showing that our method can in principle be extended to a wide range of emulsions.Monodisperse, micrometer-sized hollow particles can be prepared by templating surfactant-stabilized oil-in-water emulsion droplets with silica/siloxane shells.
Keywords: Hollow particles; Colloids; Emulsion templating; Surfactants; Encapsulation; Microspheres; Organo–silica;

Reaction and stabilizing mechanism of the cross-type macromonomers in the dispersion polymerization of styrene by Hyejun Jung; Kijong Song; Kangseok Lee; Byung H. Lee; Soonja Choe (130-141).
The cross-type (C-VUM) and linear-type (L-VUM) bifunctional vinyl urethane macromonomers and polystyrene (PS) using these macromonomers were synthesized in the dispersion polymerization in ethanol, and the reaction and stabilizing mechanism of the macromonomers was proposed. The structural verification of the macromonomers and PS was studied using 1H NMR. The weight-average particle size of C-PS (PS prepared with C-VUM) and L-PS (PS prepared with L-VUM) decreased from 4.41 to 1.36 μm and from 3.56 to 1.52 μm, whereas the average-molecular weight of those increased from 34,100 to 100,500 g/mol and from 32,200 to 71,800 g/mol, respectively. The XPS result showed that the C-PS was anchored with a larger amount of PEG than that of the L-PS on the particle surface. Thus, the reaction and stabilizing mechanism of the macromonomers for the formation of PS particles is proposed as the following. The particle surface of the C-PS is surrounded by a large amount of tail shaped macromonomers leading to higher molecular weights and smaller particle sizes. On the other hand, the particle surface of the L-PS is comprised of relatively small amounts of loop shaped macromonomers inducing lower molecular weights and larger particles of L-PS than C-PS.Polystyrene particles using the cross-type (C-VUM) and linear-type (L-VUM) macromonomer were synthesized in the dispersion polymerization. Some of the L-VUMs are suggested to exist on the particle surface as a loop-type. Whereas, the reaction and stabilizing mechanism of C-PS is dominated by the geometric structure of the C-VUMs.
Keywords: Cross-type vinylurethane macromonomer; Linear-type macromonomer; Stabilizing mechanism; Dispersion polymerization; Polystyrene;

Comparative characterization of polymethylsiloxane hydrogel and silylated fumed silica and silica gel by V.M. Gun'ko; V.V. Turov; V.I. Zarko; E.V. Goncharuk; I.I. Gerashchenko; A.A. Turova; I.F. Mironyuk; R. Leboda; J. Skubiszewska-Zięba; W. Janusz (142-156).
Polymethylsiloxane (PMS) hydrogel ( C PMS = 10   wt % , soft paste-like hydrogel), diluted aqueous suspensions, and dried/wetted xerogel (powder) were studied in comparison with suspensions and dry powders of unmodified and silylated nanosilicas and silica gels using 1H NMR, thermally stimulated depolarization current (TSDC), quasielastic light scattering (QELS), rheometry, and adsorption methods. Nanosized primary PMS particles, which are softer and less dense than silica ones because of the presence of CH3 groups attached to each Si atom and residual silanols, form soft secondary particles (soft paste-like hydrogel) that can be completely decomposed to nanoparticles with sizes smaller than 10 nm on sonication of the aqueous suspensions. Despite the soft character of the secondary particles, the aqueous suspensions of PMS are characterized by a higher viscosity (at concentration C PMS = 3 – 5   wt % ) than the suspension of fumed silica at a higher concentration. Three types of structured water are observed in dry PMS xerogel (adsorbed water of 3 wt%). These structures, characterized by the chemical shift of the proton resonance at δ H ≈ 1.7 , 3.7 , and 5 ppm, correspond to weakly associated but strongly bound water and to strongly associated but weakly or strongly bound waters, respectively. NMR cryoporometry and QELS results suggest that PMS is a mesoporous–macroporous material with the textural porosity caused by voids between primary particles forming aggregates and agglomerates of aggregates. PMS is characterized by a much smaller adsorption capacity with respect to proteins (gelatin, ovalbumin) than unmodified fumed silica A-300.Branched polymethylsiloxane molecules form primary nanoparticles ( < 10   nm ) structured in soft mesoporous/macroporous secondary particles (0.1–5 μm) with textural porosity responsible for adsorption of proteins and other macromolecules.
Keywords: Polymethylsiloxane hydrogel; Silylated fumed silica; Silica gel; Aqueous suspension; Structured water; Morphology; Structural characteristics; 1H NMR; TSDC; QELS; Rheometry; Protein adsorption;

A solution chemistry method for transforming polycrystalline Ag spherical particles into single crystalline triangular Ag nanoplates has been developed. The synthesis consists of three consecutive steps: (1) the synthesis of Ag nanospheres by NaBH4 reduction of AgNO3 in the presence of sodium citrate; (2) the conversion of citrate-stabilized Ag nanospheres into SDS (sodium dodecyl sulfate)-stabilized Ag nanospheres, and (3) the aging of the SDS-stabilized Ag nanospheres in 0.01 M NaCl solution. Our study indicates that the shape evolved through a Ag nanoparticle dissolution- and re-deposition process; and demonstrated the critical role of SDS in the process: SDS regulates the dynamics in the dissolved O2/Cl etching of the Ag nanospheres and the reduction of the released Ag+ by citrate ions in the same solution. SDS also functions as a shape-directing agent to assimilate the Ag0 atoms into single crystalline triangular Ag nanoplates. A model for the shape conversion is also proposed which provides the clue for the synthesis of anisotropic Ag nanoparticles with other shapes (rods, wires, cubes, etc.).Conversion of silver nanospheres to triangular nanoplates induced by a dissolution–recrystallization mechanism.
Keywords: Ag nanosphere; Ag nanoplate; SDS; Conversion;

A new regular polyampholyte, namely poly-(N,N-dially-N,N-dimethylammonium-alt-N-octyl-maleamic carboxylate), was synthesized by alternating free radical copolymerization. The influence of the added polymer on the range of the inverse micellar region (L2 phase) of a SDS-based system was investigated. The phase behavior as well as conductivity measurements indicate that the polymer, which forms hydrophobic microdomains, is located more in the water core of the microemulsion droplets rather than at the interface of the surfactant film. The polyampholyte proved to be an efficient reducing and stabilizing agent for the formation of gold colloids. The process of nanoparticle formation was investigated in the absence of any other reducing agent, in water as well as in the microemulsion template phase. In both cases, nanoscalic gold particles can be synthesized, while the adsorption of the polymer on the particle surface prevents their aggregation due to electrosteric stabilization.
Keywords: Polyampholyte; Microemulsion; Gold nanoparticles;

Diffusion of one or more components of a silane adhesion-promoting mixture into poly(methyl methacrylate) by Cheryl L. Loch; Dongchan Ahn; Anne V. Vázquez; Zhan Chen (170-175).
The surface-sensitive technique of sum frequency generation (SFG) vibrational spectroscopy has been applied to study the buried interfaces between different polymers including deuterated polystyrene (d-PS) and deuterated poly(methyl methacrylate) (d-PMMA) and a two-component silane adhesion-promoting mixture (SAPM) composed of (3-glycidoxypropyl)trimethoxysilane (γ-GPS) and a methylvinylsiloxanol (MVS). Because of the dissolution of d-PS, no SFG C―H stretching signals could be collected from the d-PS/γ-GPS interface, and SFG signals collected from the d-PS/SAPM interface gradually disappeared over time. SFG results also showed that γ-GPS can diffuse through the d-PMMA film. The diffusion of γ-GPS through the d-PMMA film was confirmed by SFG studies on the interface between γ-GPS and a d-PMMA/PS two-polymer layer system. Initially the SFG signal from the PS layer was detected. However, after γ-GPS diffused through the d-PMMA film, the PS film was dissolved by the silane, and thus the SFG signal from PS was lost. Similar experiments have been carried out at the interface between the SAPM and the d-PMMA/PS two-polymer layer system and it was found that the diffusion time of the γ-GPS in the SAPM through the d-PMMA film was significantly longer. These results were much different to those from previous SFG studies on the analogous PET interfaces and appear consistent with differences in solubility parameters calculated for these systems.
Keywords: Diffusion; Sum frequency generation; Adhesion promoter; Silane; Interface;

The synthesis of mesoporous SBA-15 coated with the preformed precursor of microporous aluminophosphate (AlPO) has been reported. The physicochemical properties of the coated samples were investigated by using XRD, FT-IR, N2-adsorption, ICP, 29Si MAS NMR, NH3-TPD and CO2-TPD. The characterization results suggest that the nanometer-scaled zeolite units are present on the wall surface of SBA-15, thus bringing the weak acid–base characteristics to the resulting mesoporous materials, and that the acid–base properties of these materials can be modified by the aging treatment in glycol. Moreover, vapor-phase O-methylation of catechol with methanol has been studied on these coated samples as catalysts. It is found that the coated sample bearing suitable weak acid–base sites exhibits the relatively high activity and selectivity to guaiacol.
Keywords: Aluminophosphate; Mesoporous materials; Precursor; Coating; SBA-15;

The aim of this work was to study the effect on the fouling of anion-exchange membranes (AEM) of (1) the pH value of the concentrate solution and (2) the composition in calcium, carbonate, and protein of the diluate solution to be treated by conventional electrodialysis. It appeared that after demineralization of solutions containing CaCl2 using a concentrate solution maintained at a pH value of 7 or 12, mineral fouling appeared on the AEM surface in contact with the concentrate. The mineral deposits presented a cylindrical filament shape for conditions with a concentrate solution pH value of 7, while, for a pH value of 12, the mineral deposit had a crumbly and spongy texture formed by irregular aggregates. The nature of the fouling was identified as a calcium phosphate with or without calcium hydroxide. In addition, gel-like protein fouling was detected on the AEM surface in contact with the diluate after demineralization procedures using a concentrate pH value of 2 or 7, regardless of the mineral composition of the diluate.On surfaces in contact with concentrate, mineral deposits presenting a filament shape or a sponge texture were observed, while gel-like protein fouling was detected on surfaces in contact with diluate.
Keywords: Electrodialysis; Anion-exchange membrane; Fouling; Protein; Calcium; Carbonate; pH;

A novel color removal adsorbent from heterocoagulation of cationic and anionic clays by Qiuhong Hu; Zhiping Xu; Shizhang Qiao; Fouad Haghseresht; Michael Wilson; Gao Qing Lu (191-199).
We report the preparation and characterization of a novel nanocomposite adsorbent for anionic dye removal. The nanocomposite adsorbent was prepared by heterocoagulation of delaminated bentonite and layered double hydroxide (LDH) colloids. The effects of preparation conditions, LDH loading, particle size, and calcination temperature of the modified material on the physicochemical properties of this composite adsorbent have been investigated. The optimal conditions for best Reactive Yellow 2 (RY2) dye removal efficiency are a weight ratio of LDH to bentonite of 1:1, LDH particle size 100 nm, and calcination temperature 673 K. The adsorption equilibrium data can be fitted well by the widely accepted adsorption isotherm models.After modification, the small flakes of LDH nanoparticles seem to be bound onto the bentonite surface, evidenced by a large number of overlapped hexagonal LDH structures on the bentonite surface.
Keywords: Color removal; Adsorbent; Bentonite; Layered double hydroxide; Clay;

The effects of acoustic wave propagation on the transport of colloids in saturated porous media were investigated by injecting Uranine (conservative tracer) as well as blue and red polystyrene microspheres (colloids of different diameters; 0.10 and 0.028 μm, respectively) into a column packed with glass beads. Experiments were conducted by maintaining the acoustic pressure at the influent at 23.0 kPa with acoustic frequencies ranging from 30 to 150 Hz. The experimental results suggested that colloid size did not affect the forward and reverse attachment rate coefficients. The acoustic pressure caused an increase in the effective interstitial velocity at all frequencies for the conservative tracer and colloids of both sizes, with maximum increase at 30 Hz. Furthermore, acoustics enhanced the dispersion process at all frequencies, with a maximum at 30 Hz.The effects of acoustic wave propagation on the transport of colloids in saturated porous media were investigated with the apparatus shown. Acoustics increased effective interstitial velocity and the dispersion process.
Keywords: Colloid transport; Acoustic waves; Enhanced transport; Subsurface transport; Polystyrene microspheres;

Porous polyoxometalate–tantalum pentoxide (POM/Ta2O5, POM = H3PW12O40 and H6P2W18O62) nanocomposites with different Keggin or Dawson unit loading levels (5.6–15.3%) were successfully prepared via hydrolysis of TaCl5 in the presence of POM without the addition of any structure-directing reagent. Several characterization techniques, inductively coupled plasma atomic emission spectroscopy (ICP-AES), UV–vis diffuse reflectance spectroscopy (UV–vis/DRS), Fourier transform infrared (FT-IR), 31P magic-angle spinning (MAS) NMR, field emission scanning electron microscopy (FESEM), and nitrogen adsorption/desorption analysis were combined to confirm the structure integrity of the Keggen or Dawson unit in as-prepared composites and to investigate the optical absorption properties, morphology, and surface textural properties of the composites. The enhanced photocatalytic activity of the composites compared with that of solitary POM units or Ta2O5 was evaluated through decomposition of salicylic acid (SA) and rhodamine B (RB) under visible-light excitation. The large BET surface area (129.7–188.8 m2 g−1) and porous structure, small particle size (20–25 nm), homogeneous dispersion of the POM unit within Ta2O5 framework, decreased bandgap energy, and strong electron acceptance ability of POM can explain this high photocatalytic activity of the composites.Porous polyoxometalate–tantalum pentoxide nanocomposites (H3PW12O40/Ta2O5 and H6P2W18O62/Ta2O5) were prepared for the first time, and they exhibited visible-light photocatalytic activity for decomposition of aqueous salicylic acid and rhodamine B.
Keywords: Visible-light photocatalysis; Sol–gel; Porous materials; Polyoxometalate; Tantalum pentoxide;

Hydration of a Na+-montmorillonite studied by thermally stimulated depolarization current by H. Belarbi; A. Haouzi; J.M. Douillard; J.C. Giuntini; F. Henn (216-221).
Thermally stimulated depolarization current (TSDC) technique is a powerful tool for probing dipole re-orientational motions in condensed matter. In the case of cation-exchangeable aluminosilicates, it allows the assessment of the potential barrier related to the hopping mechanism of cations and, consequently, the measurement of its evolution when molecules, i.e. water, are adsorbed and interact with the cations embedded in the solid framework. Then, using suitable models based on thermodynamics, the analysis of TSDC signals obtained at various hydration states provides insights about the surface properties of the studied solid and the mechanism of adsorption at the cationic site. In this work, TSDC is used to study the first stage, i.e. when the number of adsorbed molecules is below the occurrence of the water monolayer, of water adsorption in a Na+-montmorillonite from Mostaganem (Algeria). It is shown that the hydration process follows two stages. Using the “chemical force” concept it can then be concluded that when the number of adsorbed water molecules per cation is lower than 2, cation–water interaction dominates the energetics of adsorption, whereas at higher water loading the water “chemical force” is also involved into water–water and/or water–clay framework interactions. The number of water molecules for the monohydrated state is found to be about 7.The earliest hydration stages of a Na+-montmorillonite are studied using thermally stimulated current spectroscopy. Using the “chemical force” concept, it is concluded that when the number of adsorbed water molecules per cation is lower than 2, cation–water interaction dominates the energetics of adsorption, whereas at higher water loading the water “chemical force” is also involved into water–water and/or water–clay framework interactions.
Keywords: Clays; Montmorillonite; Thermally stimulated current; Hydration; Adsorption; Cation dynamics;

Three minimum wet thickness regions of slot die coating by Yu-Rong Chang; Hsien-Ming Chang; Chi-Feng Lin; Ta-Jo Liu; Ping-Yao Wu (222-230).
An experimental study was carried out to determine the minimum wet thickness of slot die coating for low-viscosity solutions. There exist three distinct coating regions (I, II, and III), depending on the physical properties of the coating fluid, die geometry, and flow conditions. A critical Reynolds number was found, below which viscous and surface tension effects are important. In Region I, the minimum wet thickness increases with increasing capillary number and becomes independent of capillary number in Region II. Region III exists above the critical Reynolds number where fluid inertia is dominant. In this region, the minimum wet thickness decreases as Reynolds number increases. Flow visualization on the coating bead reveals that the position of the downstream meniscus of the coating bead determines the types of coating region, whereas the shape and position of the upstream meniscus determine the type of coating defects. It was also observed that the downstream meniscus was not located at the die lip corner and both the static and dynamic contact angles varied under different conditions. These findings are critical for realistic theoretical study of slot die coating.Three distinct regions of slot die coating were found through a flow visualization technique. The fluid inertial force is important if the Reynolds number is greater than 20.
Keywords: Slot die coating; Minimum wet thickness; Capillary number; Reynolds number; Flow visualization; Static and dynamic contact angles;

Transport of wetting liquid plugs in bifurcating microfluidic channels by Cédric P. Ody; Charles N. Baroud; Emmanuel de Langre (231-238).
A plug of wetting liquid is driven at constant pressure through a bifurcation in a microchannel. For a plug advancing in a straight channel, we find that the viscous dissipation in the bulk may be estimated using Poiseuille's law while Bretherton and Tanner's laws model the additional dissipation occurring at the rear and front interfaces. At a second stage, we focus on the behavior of the plug flowing through a T-junction. Experiments show the existence of a threshold pressure, below which the plug remains blocked at the entrance of the junction. Above this required pressure, the plug enters the bifurcation and either ruptures or splits into two daughter plugs, depending on the applied pressure and on the initial length of the plug. By means of geometrical arguments and the previously cited laws, we propose a global model to predict the transitions between the three observed behaviors.The transport of wetting liquid plugs in straight and bifurcating microchannels is studied experimentally and theoretically. Three behaviors were observed at the bifurcation: blockage, rupture and splitting.
Keywords: Microfluidic bifurcation; Plug rupture; Threshold pressure; Splitting;

This paper reports the preparation and characterization of pure Langmuir and Langmuir–Blodgett (LB) films of a stilbene derivative containing two alkyl chains, namely 4-dioctadecylamino-4′-nitrostilbene. Mixed films incorporating docosanoic acid and the stilbene derivative are also studied. Brewster angle microscopy (BAM) analysis has revealed the existence of randomly oriented three-dimensional (3D) aggregates, spontaneously formed immediately after the spreading process of the stilbene derivative onto the water surface. These 3D aggregates coexist with a Langmuir film that shows the typical gas, liquid, and solid-like phases in the surface pressure and surface potential vs area per molecule isotherms, indicative of an average preferential orientation of the stilbene compound at the air–water interface, and a gradual molecular arrangement into a defined structure upon compression. A blue shift of 55 nm of the reflection spectrum of the Langmuir film with respect to the spectrum of a chloroform solution of the nitrostilbene indicates that two-dimensional (2D) H-aggregates are formed at the air–water interface. The monolayers are transferred undisturbed onto solid substrates with atomic force microscopy (AFM) revealing that the one layer LB films are constituted by a monolayer of the stilbene derivative together with some 3D aggregates. When the nitrostilbene compound is blended with docosanoic acid, the 3D aggregation is avoided in the Langmuir and Langmuir–Blodgett films, but does not limit the formation of 2D H-aggregates, desirable for second-order nonlinear optical response in the blue domain. The AFM images of the mixed LB films show that they are formed by a docosanoic acid monolayer and, on the top of it, a bilayer of the stilbene derivative.Langmuir and Langmuir–Blodgett films of 4-dioctadecylamino-4′-nitrostilbene were fabricated. Two-dimensional H-aggregates with a blue shift of 55 nm with respect to the solution are formed as shown in the figure.
Keywords: Langmuir films; Langmuir–Blodgett films; Push–pull stilbene; H-aggregates;

Studies of the rate of water evaporation through adsorption layers using drop shape analysis tensiometry by V.B. Fainerman; A.V. Makievski; J. Krägel; A. Javadi; R. Miller (249-253).
With modified measuring procedure and measuring cell design in the drop profile tensiometer PAT, it became possible to study the rate of water evaporation through adsorbed or spread surface layers. This method was employed to measure the rate of water evaporation from drops covered by adsorbed layers of some proteins and surfactants, in particular n-dodecanol. It was shown that the formation of dense (double or condensed) adsorbed layers of protein and the formation of 2D-condensed n-dodecanol layer decrease the water evaporation rate by 20–25% as compared with pure water. At the same time, the adsorbed layers of ordinary surfactants (sodium dodecyl sulfate and nonionic ethoxylated surfactant C14EO8) do not affect the water evaporation rate remarkably.Using the drop profile analysis tensiometer PAT-1, it is possible to study the rate of water evaporation through adsorbed surface layers. Adsorbed layers of protein and 2D-condensed n-dodecanol layer decrease the water evaporation rate by 20–25% while SDS does not affect the water evaporation rate remarkably.
Keywords: Dynamic surface tensions; Drop profile analysis; Water evaporation; Surfactant adsorption layers;

Room temperature synthesis of HgTe nanocrystals by Lin Song Li; Hongzhe Wang; Yongcheng Liu; Shiyun Lou; Yongqiang Wang; Zuliang Du (254-257).
We report a new method to synthesize monodisperse zinc blende HgTe nanocrystals at room temperature in noncoordinating solvent—octadecene. Thiol was needed to control the reaction at a suitable nucleation and growth speed. In the early stage of the reaction, HgTe nanocrystals formed aggregates, and then the aggregates were dispersed and individual dot-shaped nanocrystals were formed with stronger photoluminescence emitting. UV–vis, photoluminescence, and TEM have been used to study the properties of as-prepared HgTe nanocrystals.
Keywords: HgTe; Near-IR; Nanocrystals;

Surfactant-assistant and facile synthesis of hollow ZnS nanospheres by Lihong Dong; Ying Chu; Yanping Zhang; Yang Liu; Fuyong Yang (258-264).
Small and monodisperse ZnS hollow nanospheres with outer diameter ranging from 60 to 70 nm and wall thickness of 15–20 nm were fabricated in a large scale by a simple surfactant polyethylene glycol (PEG) assisted method. The diameter and the wall thickness of the hollow nanospheres could be controlled by manipulating the amount of PEG and the aging time, respectively. Moreover, the wall of these hollow nanospheres is very compact. The product was characterized by X-ray power diffraction (XRD), transmission electron microscopy (TEM), UV–vis spectrum and fluorescence spectroscopy. The photocatalytic activity of as-prepared ZnS hollow nanospheres was also evaluated by using methyl orange (MO) as a model organic compound and the result revealed that their photocatalytic activity is a little lower than that of Degussa P25 TiO2 but better than that of ZnS nanocrystals prepared by literature method. Furthermore, a rational mechanism to the formation and evolution of the products is proposed.Small and monodisperse ZnS hollow nanospheres with outer diameter ranging from 60 to 70 nm and wall thickness of 15–20 nm were fabricated in a large scale by a simple surfactant assisted micelle method. The diameter and the wall thickness of the hollow nanospheres could be controlled by manipulating the amount of PEG and the aging time, respectively. The photocatalytic investigation revealed that the product as-obtained had better photocatalytic activity.
Keywords: ZnS; Hollow nanospheres; Photocatalytic activity;

Long α-Fe2O3 hollow fibers have been prepared through a facile sol–gel combined co-electrospinning technique using ferric citrate as precursor, and α-Fe and γ-Fe2O3 hollow fibers have been obtained by reduction and reoxidation at different conditions. The outer diameter of the as-prepared hollow fibers is 0.5–5 μm with wall thickness of 200–800 nm. The obtained tubular fibers were characterized by thermal gravimetric (TG), FT-IR spectra, X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and Raman techniques. In addition, magnetic properties of α-Fe and γ-Fe2O3 hollow fibers have also been investigated.Long α-Fe2O3 hollow fibers have been prepared through sol–gel method combined with co-electrospinning technology, and α-Fe and γ-Fe2O3 hollow fibers have been obtained by deoxidize at different conditions.
Keywords: α-Fe2O3; α-Fe; γ-Fe2O3; Hollow fibers; Co-electrospinning; Sol–gel processing; Ferric citrate;

Hydrothermal fabrication and characterization of polycrystalline linneite (Co3S4) nanotubes based on the Kirkendall effect by Xiangying Chen; Zhongjie Zhang; Zhiguo Qiu; Chengwu Shi; Xueliang Li (271-275).
In this study, polycrystalline linneite (Co3S4) nanotubes constructed with nanoparticles have been firstly fabricated using 1D Co(CO3)0.35Cl0.20(OH)1.10 nanowires as the sacrificial templates under hydrothermal conditions. The samples are characterized by means of XRD and TEM. The formation mechanism of the Co3S4 nanotubes can be explained by the nanoscale Kirkendall effect, which results from the difference in diffusion rates between cobalt source and hydrogen sulfide. This simple synthetic route is expected to prepare other nanomaterials with the tubular structures.Hydrothermal fabrication and characterization of polycrystalline linneite (Co3S4) nanotubes based on the Kirkendall effect.
Keywords: Hydrothermal; Linneite; Nanotubes; Kirkendall effect;

RBM band shift-evidenced dispersion mechanism of single-wall carbon nanotube bundles with NaDDBS by Shigenori Utsumi; Mamiko Kanamaru; Hiroaki Honda; Hirofumi Kanoh; Hideki Tanaka; Takahiro Ohkubo; Hideki Sakai; Masahiko Abe; Katsumi Kaneko (276-284).
The dispersion process of single-wall carbon nanotube (SWNT) by using sodium dodecylbenzene sulfonate (NaDDBS) was studied by means of surface tension measurements, ultraviolet–visible (UV–Vis) spectroscopy, scanning electron microscopy (SEM), and transmission electron spectroscopy (TEM). The critical micelle concentration (CMC) and the concentration where the surface tension begins to drop increase by the presence of SWNT. The isotherm of NaDDBS amount adsorbed on SWNT shows the plateau region at 0.2–6 mM and the saturated region above 40 mM. The external surface of SWNT bundle is fully covered with adsorbed NaDDBS at the plateau region, showing that SWNTs can be dispersed with the bundle form. On the other hand, SWNTs are dispersed in individual tubes at the saturated region, where the adsorption amount corresponds to coating of individual tube surfaces with NaDDBS. This dispersion state was confirmed by SEM and TEM observations. The effect of the dispersion state of SWNTs on radial breathing mode in Raman spectrum gave inherent peak shifts, being the in situ evidences on the step-wise dispersion mechanism of the SWNT bundle to the individual tubes.
Keywords: Single-wall carbon nanotube; Bundle structure; NaDDBS; Dispersion; Surface tension; Adsorption isotherm; Raman spectroscopy; Radial breathing mode;

Observation of characteristic IR band assignable to dimerized copper ions in montmorillonite by Masashi Tanaka; Atsushi Itadani; Takahiro Abe; Hideki Taguchi; Mahiko Nagao (285-288).
Copper ion-exchanged montmorillonite clays, which had been prepared by ion exchange in an aqueous solution of CuCl2 at a temperature above 323 K, exhibited the characteristic IR band in the region 3360–3310 cm−1. No such bands were observed for the samples prepared by using different ion-exchange solutions and at different temperatures. From the spectroscopic observations, it was revealed that the ion-exchanged copper ions (Cu2+) are in the form of dimerized species by bridging two hydroxyls, [ Cu 2 + < ( OH − ) 2 > Cu 2 + ], in montmorillonite.It was revealed that the dimerized Cu2+ ions bridging two hydroxyls are formed in montmorillonite by ion exchange in an aqueous solution of CuCl2 at a temperature above 323 K.
Keywords: Montmorillonite; Dimerized copper ions; Monovalent copper ion;

by Arthur Hubbard (289).