Journal of Colloid And Interface Science (v.303, #1)

Surface-enhanced Raman scattering (SERS) spectra of p-, m-, and o-nitroaniline (PNA, MNA, and ONA) adsorbed on gold nanoparticles were studied, respectively, in a gold colloidal solution and on dried gold-coated filter paper. Significant changes were found in the SERS spectra of p-, m-, and o-nitroaniline molecules adsorbed on the two substrates, indicating that the behavior of p-, m-, and o-nitroaniline adsorbed on gold nanoparticles coated on filter paper was different from that in gold aqueous colloids. Moreover, on the filter paper it was found that the SERS spectra of the PNA molecules changed with the coverage density of the gold nanoparticles, while the MNA and ONA did not evidently change. The analyses showed that the origins of these changes were the different adsorption behavior of molecules adsorbed on the gold nanoparticles and that the adsorption behavior of molecules was greatly affected by the surface characteristic of the substrate and the surface configuration of the adsorbate. In addition, the vibrational frequencies and Raman scattering intensities of the three nitroanilines were calculated by use of the density functional theory (DFT-B3LYP/6-31G(d)) method. The combination of SERS spectroscopy and DFT calculation is quite useful for studies of adsorption orientation of a molecule on a metal nanoparticle.Surface-enhanced Raman Scattering (SERS) spectra of p-, m-, and o-nitroaniline (PNA, MNA, and ONA) adsorbed on the gold nanoparticles were studied, respectively, in the gold colloidal solution and on the dried gold-coated filter paper, as is shown following for PNA. The Raman spectrum of solid PNA (a), the SERS spectra of PNA in the gold colloidal solution (b) and on the gold-coated filter paper (c).
Keywords: Adsorption behavior; Surface-enhanced Raman scattering (SERS); n-Nitroaniline; Gold nanoparticles;

Pure, phosphated, and phosphonated CaO samples were prepared and characterized by X-ray powder diffractometry, FTIR spectroscopy, scanning electron microscopy, and energy-dispersive X-ray microprobing. Surface acid–base properties were probed by in situ FTIR spectroscopy of adsorbed CO (at 85 K), CDCl3 (at RT), CO2 (at RT), and methyl butynol decomposition reactions (at 473 K). Results obtained have shown phosphate and, to a larger extent, phosphonate additives to enhance the strength of Lewis acid sites exposed on CaO surfaces, at the expense of the Lewis base site strength. The phosphonation has been found, moreover, to make CaO particles grow in a preferential direction and be less susceptible to rehydration. These findings may establish surface chemical attributes for the application of the methylene bisphosphonate (MBP) class of drugs to hamper acid-induced resorption of bone materials (osteoporosis).Phosphate and, to a larger extent, phosphonate additives enhance the strength of Lewis acid sites exposed on CaO surfaces, at the expense of the Lewis base site strength. Moreover, the phosphonation renders CaO particles less susceptible to rehydration and causes them to grow in a preferential direction.
Keywords: Calcium oxide; Phosphated calcium oxide; Phosphonated calcium oxide; X-ray diffractometry; Ex situ FTIR spectroscopy; Scanning electron microscopy; Energy dispersive X-ray emission; In situ FTIR of adsorbed probe molecules; CO adsorption; CO2 adsorption; CDCl3 adsorption; Methylbutynol decomposition; Surface acid–base properties; Particle morphology;

The preparation and anion exchange properties of 3-n-propyl(4-methylpyridinium) silsesquioxane chloride polymer are described. This new polymer was prepared by the sol-gel processing method and is designated as SiPic+Cl. It is insoluble in water and showed an anion exchange capacity of 1.46 × 10 −3 mol g −1 . The adsorption isotherms of ZnCl2, CdCl2 and HgCl2 were determined from aqueous solutions and the adsorption equilibria simulations fit the model of fixed bidentate centers with the absence of lateral interactions and energetic heterogeneity between them. The metal ions diffuse into the solid solution interface and are dominantly present as MCl2− 4 species for Zn(II), MCl2− 4 and MCl 3 species for Cd(II) and MCl 3 species for Hg(II).Scheme of HgCl2 adsorption on the anion exchanger solid polymer from an aqueous solution. For zinc and cadmium, ZnCl2− 4 and CdCl2− 4 species are adsorbed on the surface.
Keywords: 3-n-Propyl(4-methylpyridinium) silsesquioxane chloride; Ion exchanger; Adsorption of MCl2 (M = Zn, Cd and Hg); Adsorption isotherms; Adsorption equilibria simulation;

XPS and XAS studies of copper(II) sorbed onto a synthetic pyrite surface by Aude Naveau; Fanny Monteil-Rivera; Emmanuel Guillon; Jacques Dumonceau (25-31).
Compounds containing copper are likely candidates to delay iodide migration in environmental media through the formation of sparingly soluble phases. Preliminary experiments showed that iodide was neither sorbed onto chalcopyrite nor by a binary system pyrite/copper(II), although significant amounts of copper were present at the pyrite surface. In the present study, spectroscopic studies (XPS, XANES and EXAFS) were thus performed to determine the nature of sorbed copper species. Although introduced as Cu(II), copper was mainly present at the oxidation state (I) on the pyrite surface suggesting a heterogeneous reduction process. Moreover, copper appeared tetrahedrally coordinated to two sulfur and two oxygen atoms onto the pyrite surface, a chemical environment, which seemingly stabilized the metal and made it unreactive towards iodide.The nature of sorbed copper(II) species onto pyrite was investigated using a combination of macroscopic and spectroscopic studies.
Keywords: Pyrite; Copper; Sorption; Reduction; XPS; Absorption spectroscopy;

Immobilization of Keggin and Preyssler tungsten heteropolyacids on various functionalized silica by Aliakbar Tarlani; Mansour Abedini; Ali Nemati; Maryam Khabaz; Mostafa M. Amini (32-38).
The Keggin and Preyssler tungsten heteropolyacids, H3PW12O40 and H15P5W30O110, have been immobilized on the inner surface of mesoporous MCM-41, fume silica and silica-gel by means of chemical bonding to aminosilane groups. The materials were characterized by FT-IR spectroscopy, low-angle XRD and BET surface area analysis. The tendencies of heteropolyacids adsorption in solution on functionalized silicas have been investigated by UV–vis. Among the functionalized silica materials, MCM-41 showed the largest amine to silica and the least heteropolyacid to silica ratios. The BET surface area revealed that in all three cases the surface area decreased after grafting amine group and anchoring of the HPAs clusters. Low-angle XRD analysis showed that by introducing HPA into functionalized MCM-41 the intensity of the main reflection decreased significantly.The Keggin and Preyssler tungsten heteropolyacids, H3PW12O40 and H15P5W30O110, have been immobilized on the surface of mesoporous MCM-41, fume silica and silica-gel by means of chemical bonding to aminosilane groups.
Keywords: Heteropolyacid; Adsorption; MCM-41; Silica; Aminosilane; Immobilization;

Reason: This paper has been retracted because of ethical conflicts resulting from the actions of one of the co-authors.The first author Mr. Sukdeb Pal worked on kinetics, adsorption isotherms and other aspects of cyanuric acid adsorption in his previous institute, Hindustan Lever Research Centre, Mumbai 400099, for several months. Modification of acid-treated carbon by ammonia also formed a part of his work done at his previous institute. Mr. Pal used data obtained at that institute as shown in Fig 1(a) and (b) in this article without due authorization from that institute. Mr. Pal did not inform the corresponding author about this fact. Mr. Pal's previous institute claims that this action infringes professional ethics.To avoid any conflict of interest and to adhere to the ethical obligations the authors have requested the retraction of the article.

The effect of acid–base titration protocol and speed on pH measurement and surface charge calculation was studied on suspensions of γ-alumina, hematite, goethite, and silica, whose size and porosity have been well characterized. The titration protocol has an important effect on surface charge calculation as well as on acid–base constants obtained by fitting of the titration curves. Variations of pH versus time after addition of acid or base to the suspension were interpreted as diffusion processes. Resulting apparent diffusion coefficients depend on the nature of the oxide and on its porosity.
Keywords: Acid–base titration; Surface charge; Oxides; Titration kinetics; Surface acid–base constants; Surface complexation;

Influence of electrolytes on the dynamic surface tension of ionic surfactant solutions: Expanding and immobile interfaces by Krassimir D. Danov; Peter A. Kralchevsky; Kavssery P. Ananthapadmanabhan; Alex Lips (56-68).
Here, we derive analytical asymptotic expressions for the dynamic surface tension of ionic surfactant solutions in the general case of nonstationary interfacial expansion. Because the diffusion layer is much wider than the electric double layer, the equations contain a small parameter. The resulting perturbation problem is singular and it is solved by means of the method of matched asymptotic expansions. The derived general expression for the dynamic surface tension is simplified for the special case of immobile interface and for the maximum bubble pressure method (MBPM). The case of stationary interfacial expansion is also considered. The effective diffusivity of the ionic surfactant essentially depends on the concentrations of surfactant and nonamphiphilic salt. To test the theory, the derived equations are applied to calculate the surfactant adsorption from MBPM experimental data. The results excellently agree with the adsorption determined independently from equilibrium surface-tension isotherms. The derived theoretical expressions could find application for interpreting data obtained by MBPM and other experimental methods for investigating interfacial dynamics.To derive analytical expressions for the dynamic surface tension of ionic surfactant solutions, we accounted for the existence of two regions near the interface: a relatively narrow electric double layer and a much wider outer diffusion layer.
Keywords: Adsorption dynamics; Dynamic surface tension; Expanding interfaces; Ionic surfactants; Maximum bubble pressure method;

Isotherm sorption of Cd2+, Co2+, and Ni2+ onto high-yield kraft fibers by Tuan D. Duong; Kien L. Nguyen; Manh Hoang (69-74).
The sorption capacity of high-yield kraft fibers for Cd2+, Co2+, and Ni2+ increased with pH and concentration of the cations in the liquid phase. Within the concentration range for the experiments, which was less than 2 mM, the experimental results fitted the Langmuir, Freundlich, and Sips models with regression coefficient greater than 0.97. Of the three cations investigated, Ni2+ had the highest sorption affinity, followed by Cd2+ and Co2+. The effect of the hydrated radius on the sorption affinity was discussed. Thermodynamically, the sorption was spontaneous and exothermic in the temperature range 283–308 K.The sorption capacity of kraft fibers for Cd2+ increases with pH due to increased degree of ionization of lignocellulosic fiber components. The sorption capacity also increased with the Cd2+ concentration.
Keywords: Heavy metal; Sorption; Kraft fiber;

Various analytical expressions for solute adsorption kinetics within porous absorbents of defined geometry (planar sheet, cylinder, and sphere) are available in the literature. However, these expressions are limited for practical numerical evaluation because they are based on infinite series. An investigation of these expressions has been carried out and then accurate but simple expressions derived that enable rapid determination of effective diffusion coefficients for adsorption within geometrically categorical absorbents. These involve directly fitting calculated kinetic adsorption curves to experimental ones. A simple one point method is also proposed to estimate the effective diffusion coefficient for an adsorption process within these simple geometrical absorbents as an initial value for a best fit.Expressions for solute adsorption kinetics within absorbents of defined geometries (planar sheet, cylinder, and sphere) are derived, and enable determination of effective diffusion coefficients by directly fitting calculated kinetic adsorption curves to experimental ones.
Keywords: Kinetics of absorption; Adsorption from solution; Bipartite expression; Direct simulation; Diffusion coefficient; Sphere; Cylinder; Planar sheet;

Adsorption of Safranin-T from wastewater using waste materials— activated carbon and activated rice husks by Vinod K. Gupta; Alok Mittal; Rajeev Jain; Megha Mathur; Shalini Sikarwar (80-86).
Textile effluents are major industrial polluters because of high color content, about 15% unfixed dyes and salts. The present paper is aimed to investigate and develop cheap adsorption methods for color removal from wastewater using waste materials activated carbon and activated rice husk—as adsorbents. The method was employed for the removal of Safranin-T and the influence of various factors such as adsorbent dose, adsorbate concentration, particle size, temperature, contact time, and pH was studied. The adsorption of the dye over both the adsorbents was found to follow Langmuir and Freundlich adsorption isotherm models. Based on these models, different useful thermodynamic parameters have been evaluated for both the adsorption processes. The adsorption of Safranin-T over activated carbon and activated rice husks follows first-order kinetics and the rate constants for the adsorption processes decrease with increase in temperature.Effect of pH on the adsorption of Safranin-T over AC and ARH.
Keywords: Safranin-T; Adsorption; Activated carbon; Activated rice husk;

Nickel and lead sequestration in manganese oxide-coated montmorillonite by Thipnakarin Boonfueng; Lisa Axe; Ying Xu; Trevor A. Tyson (87-98).
Amorphous hydrous manganese oxide (HMO) is an important mineral in soils and sediments influencing the mobility and bioavailability of metal contaminants. In this study, nickel and lead sorption to discrete HMO and HMO-coated montmorillonite was investigated mechanistically. The effect of pH and concentration revealed that when normalized to the mass of oxide present, the HMO-coated montmorillonite behaved similarly to the discrete Mn oxide, where both ions sorbed onto HMO-coated montmorillonite as inner-sphere complexes. Ni coordinated to the vacancy sites in the Mn oxide structure, while Pb formed bidentate corner-sharing complexes. These coordination environments were observed not only as a function of loading, pH, and ionic strength, but also in long-term studies where sorption increased by as much as 100% (from 6 × 10 −4 to 1.2 × 10 −3   mol   Ni / g HMO-coated montmorillonite). In this slower sorption process, intraparticle diffusion, the internal surface sites along microporous walls appear to be no different than external ones. Best fit diffusivities ranged from 10−12 to 10 −13   cm 2 / s for Ni and 10−17 to 10 −20   cm 2 / s for Pb. The significant difference in the diffusivities for the two ions is consistent with site activation theory, where theoretical surface diffusivities were predicted and given their error were in agreement with experimental results. Mn oxides sequester heavy metals in the environment.Proposed Pb and Ni sorption configurations on hydrous manganese oxide (HMO) show: (a) Pb forms bidentate corner-sharing complexes with Pb–O at 2.30 Å and Pb–Mn at 3.56 Å; (b) Ni coordinates to the vacancy site of Mn oxide with Ni–O at 2.04 Å, Ni–Mn at 3.32 Å, and Ni–Mn at 3.49 Å.
Keywords: Ni; Pb; Sorption; XAS; Mn oxide; HMO; Mn oxide coating; Montmorillonite; Intraparticle surface diffusion;

Amine-functionalized adsorbents have attracted increasing interest in recent years for heavy metal removal. In this study, diethylenetriamine (DETA) was successfully grafted (through a relatively simple solution reaction) onto poly(glycidyl methacrylate) (PGMA) microgranules to obtain an adsorbent (PGMA-DETA) with a very high content of amine groups and the PGMA-DETA adsorbent was examined for copper ion removal in a series of batch adsorption experiments. It was found that the PGMA-DETA adsorbent achieved excellent adsorption performance in copper ion removal and the adsorption was most effective at pH > 3 in the pH range of 1–5 examined. X-ray photoelectron spectroscopy (XPS) revealed that there were different types of amine sites on the surfaces of the PGMA-DETA adsorbent but copper ion adsorption was mainly through forming surface complexes with the neutral amine groups on the adsorbent, resulting in better adsorption performance at a higher solution pH value. The adsorption isotherm data best obeyed the Langmuir–Freundlich model and the adsorption capacity reached 1.5 mmol/g in the case of pH 5 studied. The adsorption process was fast (with adsorption equilibrium time less than 1–4 h) and closely followed the pseudo-second-order kinetic model. Desorption of copper ions from the PGMA-DETA adsorbent was most effectively achieved in a 0.1 M dilute nitric acid solution, with 80% of the desorption being completed within the first 1 min. Consecutive adsorption–desorption experiments showed that the PGMA-DETA adsorbent can be reused almost without any loss in the adsorption capacity.Diethylenetriamine (DETA) was successfully grafted, through a simple solution reaction, onto poly(glycidyl methacrylate) (PGMA) to obtain adsorbents with a high content of amine groups for effective adsorption of copper ions.
Keywords: Poly(glycidyl methacrylate) granules; Diethylenetriamine; Surface grafting; Adsorption; Copper ion removal;

A novel dimensionless plot strategy is developed in which multiple, independently measured macroscopic variables characterizing the same microgel phase transition are reduced onto a zero-to-one scale and simultaneously plotted. This strategy allows for direct comparisons to be made between changes in these variables over the phase transition, generating graphical “fingerprints” characteristic of specific radial and chain functional group distributions. This method is applied to study the swollen state properties of pH-induced phase transitions in five poly(N-isopropylacrylamide)-based microgels with significantly different but well-understood ―COOH functional group distributions. Radial functional group distributions identified based on this method match the distributions observed via electron microscopy, while the impact of functional group clustering on the ionization-driven swelling response can be directly identified. Change ratio plots in which the percentage changes of two different variables are plotted as mutual functions are also applied to generate semi-quantitative diagnostic parameters for probing radial functional group distributions and gaining insights into the mechanisms of gel phase transitions.A novel dimensionless plot strategy in which multiple independent measurements of a volume phase transition are plotted on the same graph is used to generate graphical “fingerprints” of functional group distributions in thermosensitive microgels.
Keywords: Microgels; Soft colloids; Poly(N-isopropylacrylamide); Morphology; Functional group distributions; Analytical methods;

Friction and forces between cellulose model surfaces: A comparison by Johanna Stiernstedt; Niklas Nordgren; Lars Wågberg; Harry Brumer; Derek G. Gray; Mark W. Rutland (117-123).
Four different cellulose model surfaces, and one silica surface, have been studied by means of atomic force microscopy (AFM). The normal interactions have been found to consist of a longer range double layer force with a short range steric interaction, the nature of which is extensively discussed. Both the surface charge and range of the steric force depend on the type of cellulose substrate used, as does the magnitude of the adhesion. Studies of friction reveal that surface roughness is the determining factor for the friction coefficient, with which it increases monotonically. The absolute value, however, is determined by the surface chemistry. All studied cellulose surfaces show similar behavior in response to xyloglucan addition.Cellulose is an important substrate for papermaking and laundry applications. The forces and friction of a set of cellulose model surfaces have been investigated by AFM cellulose colloidal probe technique.
Keywords: AFM; Cellulose; Surface forces; Colloid probe; Xyloglucan; Nanotribology; Friction;

Selective deposition of metal (Au) and oxide (SiO2) nanoparticles with a size range of 10–30 nm on patterned silicon–silicon oxide substrate was performed using the electrospray method. Electrical charging characteristics of particles produced by the electrospray and patterned area created by contact charging of the electrical conductor with non- or semi-conductors were investigated. Colloidal droplets were electrosprayed and subsequently dried as individual nanoparticles which then were deposited on substrates, and observed using field emission-scanning electron microscopy. The number of elementary charge units on particles generated by the electrospray was 0.4–148, and patterned area created by contact charging contained sufficient negative charges to attract multiple charged particles. Locations where nanoparticles were (reversibly) deposited depended on voltage polarity applied to the spraying colloidal droplet and the substrate, and the existence of additional ions such as those from a stabilizer.Colloidal nanoparticles can be dispersed in the gas-phase and deposited selectively and reversibly on a patterned substrate, by “plus/minus” electrospray and contact charge of the substrate.
Keywords: Aerosol; Coating; Colloid; Contact charging; Deposition; Droplet; Electrostatic; Patterning; Substrate; Zeta potential;

Co–Pt alloy nanoparticles produced using a template of nanoparticle array by Jung H. Kim; Jeon Kim; Chang K. Kim; Chong S. Yoon (131-136).
A monolayer of Co–Pt alloy nanoparticles in the nanometer-size regime was fabricated using a nanotemplate approach. 1.7-nm-thick Co46Pt54 film was deposited onto a preexisting array of Ni seed particles embedded in a polyimide film. During subsequent annealing, the deposited Co46Pt54 film coalesced onto the seed particles to produce a monolayer of Co–Pt alloy particles. Deposition and annealing were repeated to increase both average particle size and volume fraction of the alloy particles. It was also shown that the annealing temperature was critical in controlling the particle size distribution and the final composition of the nanoparticles. This method of forming a single layer of vertically aligned nanoparticles can be easily extended to a large area as well as to produce a different combination of alloy particles on a polymer film.
Keywords: Metallic particle; Polyimide; Monolayer; Template;

Effect of cationic surfactant adsorption on the rheological and surface properties of bentonite dispersions by Ebru Günister; Sevim İşçi; Nevin Öztekin; F. Bedia Erim; Ö. Işık Ece; Nurfer Güngör (137-141).
In this study, the adsorption, bridging, and intercalation effects of a cationic surfactant, benzyldimethyltetradecyl ammonium chloride (BDTDACl), on bentonite clay suspensions was investigated. The adsorption, rheological behaviors, and colloidal properties of the clay dispersions were determined as a function surfactant concentration. Adsorption isotherms were obtained using the batch-equilibrium technique. The rheological behavior of the clay suspensions was obtained by shear stress-shear rate measurements within 0–350 s−1 shear rates. The structure of the composite particles was analyzed by using X-ray diffraction analysis and it was found that the expansions of basal d-spacings are less than 16.80 Å, suggesting a monolayer structure.Around 6 mmol/L surfactant addition gives the maximum flocculation, as after further addition the system begins defloculate.
Keywords: Bentonite; Cationic surfactant; Adsorption; Rheology; Zeta potential;

Nanocrystalline TiO2 powders were rapidly prepared by hydrolysis of Ti(OC4H9)4 under ultrasound irradiation. The influences of acids (HCl, HNO3, and H2SO4) and their corresponding salts (NaCl, KNO3, and Na2SO4) on the crystalline phase and morphology of products were investigated, respectively. Compared with NaCl and KNO3 that show no evident influence on the crystalline phase, HCl and HNO3 have a decisive influence on the crystalline phase of the products. However, both H2SO4 and Na2SO4 are favorable for the formation of anatase. By adjusting the concentration of SO2− 4 in the reaction medium, the contents of anatase and rutile phases in the TiO2 powders can be successfully controlled. The morphology of TiO2 crystallites are shown to be strongly related to the type of acid used in the reaction medium.
Keywords: TiO2; Nanocrystals; Crystalline phase; Morphology; Ultrasound irradiation;

A method to determine the fractal dimension of diesel soot agglomerates by Magín Lapuerta; Rosario Ballesteros; Francisco J. Martos (149-158).
Soot agglomerates emitted by diesel engines are composed of primary particle forming irregular clusters. Such irregularity can be quantified by the fractal dimension, whose determination depends on certain parameters not unanimously established, such as the prefactor of the power law relationship. Mean values of the fractal dimension of large collections of agglomerates are usually determined in literature by least-square regression fittings to the power law relationship. In this paper, an iterative method to determine the fractal dimension of individual agglomerates is proposed instead, thus making possible a better discrimination of effects. Functions depending on the fractal dimension and the number of primary particles are proposed for the prefactor and for the overlapping parameter (a measure of the overlap that the primary particles provoke among themselves when projected). Therefore, extreme cases (agglomerates forming a compact sphere and an aligned chain of primary particles) were taken as boundary conditions, for which a geometrical analysis has been performed. The method has been adjusted by comparison with cluster–cluster aggregation models taken from literature, and has proved to have good sensitivity and low loss of information. Some examples are shown from transmission electron microscopy (TEM) images of agglomerates obtained with thermophoretic sampling from the exhaust gas of a diesel engine under different operating conditions.An iterative method to determine the fractal dimension of every single agglomerate is proposed, thus making possible a better discrimination of effects. Functions depending on the fractal dimension and the number of primary particles are proposed for the prefactor and for the overlapping parameter. Extreme cases (agglomerates forming a sphere and an aligned chain) were taken as boundary conditions, for which a geometrical analysis has been performed. An abacus for the direct determination of the fractal dimension and apparent density from the image analysis is also presented.
Keywords: Diesel engines; Fractal dimension; Microscopy; Soot agglomerates;

Circular dichroism of crude oil and its derivatives. Role of permolecular structures by A.V. Potapov; S.F. Kolyakov; V.N. Krasheninnikov; B.S. Dumesh (159-163).
Petrols with different octane numbers, diesel fuel and solutions of crude oil in toluene have been studied by the methods of absorption spectroscopy, circular dichroism spectroscopy and correlation spectroscopy of scattered light. Circular dichroism signal was registered for crude oil solutions in the spectral ranges corresponding to the measured earlier resonance absorption of asphaltene solutions in toluene. We show that the optical activity of crude oil solutions is due to the aggregation of asphaltene molecules in one spectral range and is intensified with the aggregation of asphaltene molecules in another spectral range. Petrols have no optical activity. The optical activity registered for diesel fuel is possibly due to the aggregation of asphaltene molecules.
Keywords: Crude oil; Permolecular structures; Asphaltene; Circular dichroism; Optical activity; Petrol; Diesel fuel;

Calcium sulfate precipitation in the presence of water-soluble polymers by Maria G. Lioliou; Christakis A. Paraskeva; Petros G. Koutsoukos; Alkiviades C. Payatakes (164-170).
The effect of four different polymers on the precipitation of calcium sulfate was investigated in the present work. The degree of inhibition was estimated from measurements of the calcium ion activity and from specific solution conductivity measurements in the supersaturated solutions during the course of the precipitation process. The effects of polyacrylic acid (PAA, three different polymers with average molecular weight 2000, 50,000, and 240,000, respectively) and of a co-polymer of PAA with polystyrene sulfonic acid (PSA, average molecular weight < 20 , 000 ) were investigated with respect to their effect on the kinetics of spontaneous precipitation of calcium sulfate salts. The results of the kinetics experiments suggested that the spontaneous precipitation from supersaturated calcium sulfate solutions at 25 °C yielded exclusively calcium sulfate dihydrate (gypsum) both in the absence and in the presence of the polymeric additives. The induction times, preceding the formation of the solid increased in all cases in the presence of the polymeric additives. Polymer concentrations as low as 2.0 ppm increased induction time from practically zero to 10 min. The rates of precipitation were reduced according to the solutions content in the polymers added and precipitation was completely suppressed in the presence of 6.0 ppm of the polymers tested, depending on their molecular weight. The lower the molecular weight of PAA, the more efficient was the threshold inhibition and the stronger the reduction of the rates of spontaneous precipitation. PSA yielded the poorest inhibition efficiency in comparison with the PAA, possibly because of the relatively lower affinity of the sulfonate groups for the calcium ions of the surface of the solid forming. The kinetics results analysis assuming Langmuir-type adsorption of the polymeric molecules on the growing supercritical gypsum nuclei showed different affinity for the polymers tested in agreement with the respective inhibition efficiency, in the order: PAA1 > PAA2 > PSA > PAA3. The presence of the polymers in the supersaturated solutions resulted in modification of the precipitated gypsum crystals morphology.The presence of polyacrylic acid in supersaturated solutions retards the spontaneous precipitation of calcium sulfate dihydrate and causes changes of the morphology of the precipitated crystals.
Keywords: Calcium sulfate dihydrate; Gypsum; Spontaneous precipitation; Inhibition; Polyacrylic acid; Polystyrene sulfonate;

Colloidal interfacial interactions in a capillary channel under different chemical and flow conditions were studied using confocal microscopy. Fluorescent latex microspheres (1.1 μm) were employed as model colloids and the effects of ionic strength and flow conditions on colloidal retention at air–water interface (AWI) and contact line were examined in static and dynamic (flow) experiments. Colloids were preferentially attached to and accumulated at AWI, but their transport with bulk solution was non-negligible. Changing solution ionic strength in the range 1–100 mM had a marginal effect on colloidal accumulation, indicating forces other than electrostatic are involved. Flow through the open channel resembled Poiseuille flow with AWI acting as a non-stress-free boundary, which resulted in near stagnation of AWI and consequently promoted colloid accumulation. Retention on contact line was likely dominated by film-straining and was more significant in flow relative to static experiments due to hydrodynamic driving force. Modeling and dimensionless analysis of the flow behavior in the capillary channel clearly indicate the important role of apparent surface viscosity and surface tension in colloidal interfacial retention at the pore scale, providing insight that could improve understanding of colloid fate and transport in natural unsaturated porous media.Colloid interfacial retention was studied with a capillary channel. The behavior of colloids in static and flow experiments was visualized with a confocal microscope.
Keywords: Capillary channel; Colloid retention; Air–water interface; Contact line; Velocity profile;

Gravity-induced flocculation of Brownian particles in quiescent media under weak gravity by You-Im Chang; Tzu-Yen Huang; Teng-Hui Peng (185-194).
The main scope of the present paper is to study the rigorous problem of coupled gravity-induced/Brownian flocculation for the strong Brownian/weak gravity case, by solving the coupled Langevin type equations on determining the Brownian particles' collision trajectories. When comparing with the previous results, our numerical calculated flocculation rates are as good as those solutions obtained from using the singular perturbation expansion method to solve the steady state governing convective diffusion equation. Our solutions also confirm that the effect of Brownian diffusion can decrease the flocculation rates of colloidal particles under the condition of strong Brownian/weak gravity.The dimensionless interaction force diagram between two approaching particles. From this figure, it can be found that the relative magnitudes of ( F int ∗ ∗ ) max and − ( F int ∗ ∗ ) sec and the particle's N G value determine the particle flocculation behavior.
Keywords: Flocculation; Gravity; Brownian particles;

EXAFS study of U(VI) uptake by calcium silicate hydrates by M. Harfouche; E. Wieland; R. Dähn; T. Fujita; J. Tits; D. Kunz; M. Tsukamoto (195-204).
Among the different cement minerals, calcium silicate hydrates (C-S-H) are the prime candidates for heavy metal binding because of their abundance and appropriate structure. Immobilization processes of heavy metals by cementitious materials, and in particular C-S-H phases, thus play an important role in multibarrier concepts developed worldwide for the safe disposal of hazardous and radioactive wastes. In this study, the uptake of U(VI) by C-S-H has been investigated using X-ray absorption fine structure (XAFS) spectroscopy. C-S-H phases were synthesized using two different procedures: One is based on the mixing of CaO and SiO2 solids (“direct reaction” method); for the other one starting solutions of Ca and Si are used (“solution reaction” method). XAFS investigations were carried out on samples doped with U(VI). U(VI) was either sorbed onto previously precipitated C-S-H phases (sorption samples) or added during C-S-H synthesis (coprecipitation samples). The coordination environment of U(VI) in the sorption samples was found to be independent of the procedure used for C-S-H synthesis. A split equatorial oxygen shell (Oeq1: R = 2.23 – 2.27   Å ; Oeq2: R = 2.36 – 2.45   Å ), neighboring silicon atoms at short ( R = 3.07 – 3.11   Å ) and long ( R = 3.71 – 3.77   Å ) distances, and neighboring Ca atoms ( R = 3.77 – 3.81 and 4.15 – 4.29   Å ) were observed for all the samples. The structural parameters resemble those reported for uranophane. The coordination environment of U(VI) in the coprecipitation samples depends on the method used for C-S-H synthesis, and further, the spectra differ from those determined for the sorption samples. U―U backscattering contributions were observed in the samples prepared using the direct reaction method, whereas no split equatorial shell appeared in the samples prepared using the solution reaction method.The uptake of U(VI) by calcium silicate hydrates (C-S-H) has been investigated using X-ray absorption fine structure spectroscopy. C-S-H phases were synthesized using two different procedures. U(VI) was either sorbed onto previously precipitated C-S-H phases (sorption samples) or added during C-S-H synthesis (coprecipitation samples). The coordination environment of U(VI) in the sorption samples was found to resemble that of U(VI) in uranophane (see figure).
Keywords: C-S-H; Uranium; XAFS; Wavelet; Adsorption; Coprecipitation;

Luminescence techniques and characterization of the morphology of polymer latices by I. Soutar; L. Swanson; T. Annable; J.C. Padget; R. Satgurunathan (205-213).
Five poly(n-butyl methacrylate), PBMA, latex dispersions have been prepared, each incorporating a different fluorescent label, via a two-stage seeded emulsion polymerization. The resultant latices contain ca. 35% by weight total solids and are of 80 ( ± 10 ) nm diameter as determined by photon correlation spectrometry. Luminescence spectroscopic techniques, namely fluorescence (and phosphorescence) excited state lifetime measurements in addition to time-resolved anisotropy experiments have provided useful information regarding the morphology, microviscosity and water permeability of the resultant particles. A picture of the PBMA colloid emerges of an interior which is highly viscous and water impermeable in nature. Indeed, the environment is protective enough to sustain room temperature stabilized phosphorescence from both an acenaphthylene and 9-phenanthrylmethyl methacrylate labeled dispersion through simple nitrogen purging of the solutions. However, the current spectroscopic measurements should be viewed with the knowledge that each luminescent label may fashion its own distinctive microenvironment within the latex during polymerization.The first reported use of fluorescence time-resolved anisotropy measurements on labeled latex dispersions reveal highly viscous particle interiors. However, the labels may fashion their own local environment during polymerization.
Keywords: Poly(n-butyl methacrylate); Latices; Fluorescence; Phosphorescence; Time-resolved anisotropy measurements; Morphology; Polymer colloids;

Parsons–Zobel plots can in principle be used to estimate inner Helmholtz-layer capacitance values and electrochemical surface areas for mineral particles. Their application to aqueous suspensions of various minerals has been documented in the literature. For the experimental data used so far, the expected linear relationship between the overall and the diffuse-layer capacitances has been reported. The extracted values either have not been used at all subsequently in a surface complexation model to describe the mineral surface charge versus pH curves, or were found not to be suitable entirely for such purposes. In the latter case, the reported failure was not explained. In one part of the present paper, the Parsons–Zobel plot concept is tested with data generated from a surface complexation model, for which the interfacial structure closely corresponds to that assumed in the application of the Parsons–Zobel plot. From the analysis of the results it turns out that electrolyte binding and non-Nernstian surface potential–pH curves more or less strongly affect the outcome of Parsons–Zobel plots. Despite the fact that the analysis in this paper is restricted to iron(III) minerals only, it is concluded, in general, that the use of Parsons–Zobel plots with aqueous mineral suspensions to determine inner Helmholtz-layer capacitances for subsequent application to surface complexation models cannot be recommended, since the reasons for failure can be traced very nicely with applications to model-generated data. Such application requires the determination of further parameters, and it was found that low electrolyte binding and Nernstian slopes should be imposed. Of these two issues, the more important is electrolyte binding. For the surface complexation models, an inner Helmholtz-layer capacitance and weak electrolyte binding were required for a good fit to experimental data. The values of the electrolyte binding constants required to achieve this end are in conflict with the assumptions of the Parsons–Zobel plot (absence of specific adsorption). However, these parameters would not necessarily cause specific adsorption in terms of a classical colloid chemistry definition (i.e., would not shift isoelectric points). The electrochemical surface areas were found to be in good agreement with the value used to generate the data. Based on this, there is a potential for using the approach to determine surface areas in situ from titration curves. Consequently, in a second part of the paper, Parsons–Zobel plots are applied to experimental data with the objective of determining electrochemical surface areas in situ. Application to various sets of published experimental titration data for hydrous ferric oxide yielded consistently very large electrochemical surface areas for fresh samples. This can be explained by very small particles and/or inclusion of substantial amounts of water in the suspended particles. As would be expected, the electrochemical surface area for aged ferrihydrite was found to be substantially lower.The Parsons—Zobel plot applied to model-generated data is used to elucidate the failure of this approach to obtain “reasonable” surface complexation parameters.
Keywords: Surface charge; Mineral suspensions; Surface complexation model; Parsons–Zobel plot; Specific adsorption; Nonspecific adsorption; Electrolyte binding; Specific surface area;

Surface-enhanced Raman scattering (SERS) spectra of single-walled carbon nanotubes (SWCNTs) on metal-coated filter paper are reported for the first time. Experimental results show that the metal-coated filter paper is very effective and active. The SERS spectrum not only shows that all Raman bands of SWCNTs in normal Raman scattering have been generally enhanced, but also shows many new bands, which characterize the structure of SWCNTs and the interaction between SWCNTs and silver/gold nanoparticles, arising from symmetry lowering and selection rule relaxing of SWCNTs induced by the silver/gold surface. In our case, it is difficult to separate the contributions of the electromagnetic and chemical mechanisms to the great enhancement of the Raman signal. The analysis shows that the SERS spectra of SWCNTs on the metal-coated filter paper provide convenience for probing the sample molecules with fine structures related to defects of SWCNTs, the diameter of SWCNTs, and the SERS mechanism of SWCNTs deposited on metal-coated filter paper. Moreover, this can be used as a probe technique for monitoring the synthesis quality of SWCNTs with significant higher sensitivity than other methods, which has promise of being a new technique for monitoring synthesis quality of SWCNTs.The Raman spectrum of SWCNTs (a) and the SERS of SWCNTs on the silver-coated filter paper (b).
Keywords: Single-walled carbon nanotubes; Surface-enhanced Raman spectroscopy; Filter paper;

STM study of glycine on TiO2(110) single crystal surfaces by Tingzhu Qiu; Mark A. Barteau (229-235).
The adsorption of glycine (NH2CH2COOH) was examined by scanning tunneling microscopy (STM) on TiO2(110) surfaces at room temperature. A ( 2 × 1 ) ordered overlayer was observed on the TiO2(110)-( 1 × 1 ) surface. The adsorption of acetic acid and propanoic acid was also investigated on this surface and their STM images were quite similar to that of glycine. Since acetate and propanoate are formed by dissociative adsorption of these acids on TiO2(110), it is proposed that glycine adsorbs in the same way to form a glycinate. The amino group in the glycinate adlayer structurally analogous to those formed from aliphatic carboxylic acids would be extended away from the surface and potentially free to participate in additional reactions. The underlying structure of the TiO2 surface is important in determining the structure of the glycinate adlayer; no ordering of these adsorbates was observed on the TiO2(110)-( 1 × 2 ) surface. ( 2 × 1 ) glycinate overlayer forms on the TiO2(110)-( 1 × 1 ) surface.
Keywords: Scanning tunneling microscopy; Glycine; TiO2(110) surface;

Metallomicellar catalysis: Hydrolysis of phosphate monoester and phosphodiester by Cu(II), Zn(II) complexes of pyridyl ligands in CTAB micellar solution by Fubin Jiang; Liya Huang; Xiangguang Meng; Juan Du; Xiaoqi Yu; Yufen Zhao; Xiancheng Zeng (236-242).
The catalytic hydrolysis of bis(p-nitrophenyl) phosphate (BNPP) and p-nitrophenyl phosphate (NPP) by metallomicelles composed of Cu(II) or Zn(II) complexes of bispyridine-containing alkanol ligands in CTAB micellar solution was investigated at 30 °C. The experimental results indicate that the complexes with a 1:1 ratio of ligands to metal ions for ligands 1 (1,7-bis(6-hydroxymethyl-2-pyridyl)-2,6-dioxaheptane) and 3 (1,4-bis[(6-hydroxymethyl-2-pyridyl)-2-oxapropyl]benzene) and a 1:2 ratio of ligands to metal ions for ligand 2 (1,14-bis(6-hydroxymethyl-2-pyridyl)-2,13-dioxatetradecane) in CATB micellar solution are the active species for the catalytic hydrolysis of BNPP and NPP, respectively. The ternary complex kinetic model for metallomicellar catalysis was employed to obtain the relative kinetic and thermodynamic parameters, which demonstrated the catalytic mechanism for the hydrolysis of BNPP and NPP by metallomicelles.A possible mechanism for the hydrolysis of phosphoester by metallomicelles.
Keywords: Metallomicelle; Catalysis; Phosphodiester; Phosphate monoester;

EPS biofouling in membrane filtration: An analytic modeling study by Albert S. Kim; Huaiqun Chen; Rong Yuan (243-249).
Biofouling is theoretically investigated by modeling solute transport within a biofilm, defined in this study as a swarm of solid biocolloids surrounded by liquid-like exopolymeric substances (EPS). A mathematical approach is employed to map the biofilm to an equivalent, simple spherical cell using a self-consistent method. It is found that the physical presence of EPS and their reaction with solute ions reduce the mass transfer coefficient, which significantly contributes to permeate flux decline in reverse osmosis and nanofiltration membrane processes.Biofouling in reverse osmosis and nanofiltration is theoretically investigated by modeling solute transport within a biofilm, which is defined as a swarm of solid biocolloids surrounded by liquid-like, exopolymeric substances (EPS).
Keywords: Diffusive tortuosity factor; Biofouling; Biofilm; Biocolloids; Extracellular polymeric substances (EPS); Back-diffusion;

Transparent thin (ca. 100 nm) films of silica–surfactant mesostructured materials were deposited on borosilicate glass plates and soda-lime glass tubes from aqueous solutions containing tetraethoxysilane, alkyltrimethylammonium chloride, ammonia, and methanol. By calcination in air, the films became mesoporous (BET surface area of 700–900 m2 g−1) with pore diameter 2.0–2.8 nm.Transparent films with a thickness of ca. 100 nm were deposited on glass substrates from aqueous solutions containing tetraethoxysilane, alkyltrimethylammonium chloride, methanol, and ammonia.
Keywords: Supramolecular template; Mesoporous silica; Deposition; Transparent film; Pore size;

Arrangement of tris(phthalocyaninato) gadolinium triple-decker complexes with multi-octyloxy groups on water surface by Yanli Chen; Ying Zhang; Peihua Zhu; Yingju Fan; Yongzhong Bian; Xiyou Li; Jianzhuang Jiang (256-263).
A series of five carefully designed tris(phthalocyaninato) gadolinium triple-decker complexes [Pc(R)8]Gd[Pc(R′)8]Gd[Pc(R″)8] ( R = R ′ = R ″ = H ; R = R ′ = H , R ″ = OC 8 H 17 ; R = R ″ = H , R ′ = OC 8 H 17 ; R = H, R ′ = R ″ = OC 8 H 17 ; R = R ′ = R ″ = OC 8 H 17 ) (15) were prepared and the film forming properties on water surface were systematically investigated. The limited mean molecular area obtained by π – A isotherms revealed an “edge-on” conformation for all these compounds. UV–vis absorption spectra showed red-shifted Q bands, indicating the formation of J aggregates and effective intermolecular interaction in solid film. Phthalocyanine rings were found to take tilted orientation with respect to the normal of substrate according to the polarized absorption spectroscopic measurements. Low angle X-ray diffraction results provide direct evidence and therefore clearly clarify the point, for the first time, that unsymmetrical triple-decker molecules pack on the water surface with the unsubstituted phthalocyanine ring set close to the water surface and the substituted phthalocyanine ligand with octyloxy groups lies on the top.
Keywords: Sandwich compounds; Phthalocyanine; LB film; Arrangement;

Are the mixtures of homologous surfactants ideal? by Pablo C. Schulz; José L. Rodríguez; Rossana M. Minardi; María B. Sierra; Marcela A. Morini (264-271).
The interaction between homologous surfactants in mixed micelles was studied by the Regular Solution Theory of mixed micelles. The interaction is independent of the nature of the polar head groups and attractive and the interaction parameter β M depends linearly on the difference in chain length Δ n C . The interaction becomes ideal at Δ n C = 0.75 ± 0.06 . Above Δ n C ≈ 5 , the dependence remains linear but the slope increased 2.7 times. The phenomenon is explained as the effect of the reduction of the hydrocarbon/water micelle interface and a better packing of the chains in the micelle core, caused by the inclusion of a shorter homologous surfactants. This reduction can be more effective when Δ n C ⩾ 5 .The interaction between homologous surfactants in mixed micelles is not ideal as commonly supposed in the theoretical treatments. The nonideality (represented by the interaction parameter β M ) is independent of the polar head nature, but depends on the difference in chain length ( Δ n C ) between the two components. β M is negative for Δ n C > 0.75 and becomes more attractive for Δ n C ⩾ 5 . This behavior is explained on the basis of a better packing in the micelle core and a reduction in the water/hydrocarbon contact.
Keywords: Mixed micelles; Homologous surfactants; Critical micelle concentration; Cationic surfactants; Alkyltrimethylammonium bromides;

We have studied numerically the dynamics of the microphase separation of a water–oil–surfactant system. We developed an efficient and accurate numerical method for solving the two-dimensional time-dependent Ginzburg–Landau model with two order parameters. The numerical method is based on a conservative, second-order accurate, and implicit finite-difference scheme. The nonlinear discrete equations were solved by using a nonlinear multigrid method. There is, at most, a first-order time step constraint for stability. We demonstrated numerically the convergence of our scheme and presented simulations of phase separation to show the efficiency and accuracy of the new algorithm.The surfactant concentration diffuses to the bulk region and accumulates at the interfacial region of the droplet.
Keywords: Nonlinear multigrid method; Surfactant; Phase separation; Ginzburg–Landau model;

Tunable sustained release properties of “onion-like” phospholipids multilamellar vesicles by Christiane Morkos Douaihy; Vonda Koka; Christophe Mingotaud; Fabienne Gauffre (280-287).
“Onion-type” multilamellar micro-vesicles of phospholipids (spherulites) were doped with different amounts of a cationic cosurfactant ((-)N-dodecyl-N-methylephedrinium bromide) for the purpose of controlling the sustained release of anionic drugs. Three weak acid probes (methyl red, chlorophenol red, and ibuprofen) were encapsulated in the vesicles as drug models. The kinetics and rate of release were studied by absorption spectroscopy and HPLC. The effect of probe charge (pH above and below p K a of the probes), of cosurfactant concentration and of added salt was investigated. It was found that, above p K a (i.e., when the probes are anionic), the release can be almost totally inhibited by doping the vesicles with 2.4 wt% of cationic cosurfactant. The release properties can even be finely tuned by controlling the amounts of the cosurfactant. Salt and pH effects demonstrate the role of electrostatic interactions in sustaining the release.Doping “onion-like” phospholipids vesicles with dodecylephedrinium bromide (a cationic surfactant) enables to tune the release of anionic probes (e.g., ibuprofen). The kinetics of release was investigated in various pH, salt, and concentration conditions.
Keywords: Tunable release; Encapsulation; Multilamellar vesicles; Spherulites; Onions; Phospholipids; Drug release kinetics; Electrostatic control; Cationic surfactant; Lamellar phase;

The bounded electrophoretic motion of a cylindrical particle in a circular cylindrical microchannel is explored for two cases: (1) the particle is located on the centerline of a channel (concentrically), with a symmetric wall boundary condition since gap width is constant throughout; and (2) the particle is at an eccentric location in the channel, with an asymmetric boundary condition set by the walls. The objective is to determine the effect of different boundary conditions, geometries, and physical properties on the velocity and orientation of the cylinder with respect to the boundary. A theoretical model for the motion of the cylinder is presented and the problem is solved numerically. The steady-state simulations show that the velocity of the cylinder is reduced at small gap widths for the concentric case, but the velocity is increased at small gap widths for the eccentric case. When the cylinder is angled with respect to the horizontal in the symmetric case or is near the boundary in the asymmetric case, vertical and rotational components of velocity are predicted. In such cases, transient simulations are appropriate for most accurately representing particle motion. Two such simulations are included herein and show both horizontal and vertical translation plus rotation of the particle as a function of time.Asymmetric electric field contours and fluid velocity streamlines around a cylindrical particle in a cylindrical channel, resulting in electrophoretic translation and rotation of the particle.
Keywords: Bounded electrophoresis; Cylindrical particle; Transient simulation; Eccentrically-located particle; Concentrically-located particle;

Effects of system parameters on making aluminum alloy lotus by Zhiguang Guo; Feng Zhou; Jingcheng Hao; Weimin Liu (298-305).
In the present article, stable biomimetic superhydrophobic surfaces on aluminum alloy are obtained by wet chemical etching following modification with crosslinked silicone elastomer, perfluorononane (C9F20), and perfluoropolyether (PFPE), respectively. The formation and structure of superhydrophobic surfaces were characterized by means of scanning electron microscopy (SEM), water contact angle measurement, Fourier transform infrared spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The effects of surface roughness resulted from the etching time, and the concentration of NaOH aqueous solution on the superhydrophobicity of the surfaces have been discussed in detail. The optimal surface roughness of starting material is about 0.05–0.5 μm and the resulting surface roughness should be controlled between 2.7 and 5.8 μm in order to realize the superhydrophobicity on aluminum alloy; if the concentration of NaOH aqueous solution is about 4 wt%, the best treatment time is between 2 and 4 h to form a surface roughness changing from 2.7 to 5.8 μm. The trapped air with the binary structure plays a key role in fabricating superhydrophobic surface on aluminum alloy. In other words, the unusual structure on the surface, which has a binary structure consisted of microprotrusions and nanoparticles, plays a very vital role in constructing of the stable biomimetic superhydrophobic surface on aluminum alloy.The relationships between water contact angles and the resulting surface roughness treated with 1 M aqueous solution for 2 h and then modified with PDMSVT or C9F20, respectively, showing the resulting surface roughness is vital for forming superhydrophobicity.
Keywords: Aluminum alloy; Lotus effect; Superhydrophobicity; Surface roughness; System parameters; Contact angle;

Thinning of drying latex films due to surfactant by Venkata R. Gundabala; Alexander F. Routh (306-314).
Lateral non-uniformities in surfactant distribution in drying latex films induce surface tension gradients at the film surface and lead to film thinning through surfactant spreading. Here we investigate the influence of the surfactant driven to the air–water interface, during the early stages of latex film drying, on the film thinning process which could possibly lead to film rupture. A film height evolution equation is coupled with conservation equations for particles and surfactant, within the lubrication approximation, and solved numerically, to obtain the film height, particle volume fraction, and surfactant concentration profiles. Parametric analysis identifies the effect of drying rate, dispersion viscosity and initial particle volume fraction on film thinning and reveals the conditions under which films could rupture. The results from surface profilometry conform qualitatively to the model predictions.
Keywords: Latex films; Surfactant; Film thinning; Rupture;

Stable oxide nanoparticle clusters obtained by complexation by J.-F. Berret; A. Sehgal; M. Morvan; O. Sandre; A. Vacher; M. Airiau (315-318).
We report on the electrostatic complexation between polyelectrolyte-neutral copolymers and oppositely charged 6-nm crystalline nanoparticles. For two different dispersions of oxide nanoparticles, the electrostatic complexation gives rise to the formation of stable nanoparticle clusters in the range 20–100 nm. It is found that inside the clusters, the particles are “pasted” together by the polyelectrolyte blocks adsorbed on their surface. Cryo-transmission electronic microscopy allows visualization of the clusters and determination of the probability distribution functions in size and in aggregation number. The comparison between light scattering and cryo-microscopy results suggests the existence of a polymer brush around the clusters.

Measurements of the advancing contact angle (θ) were carried out for aqueous solution of cetyltrimethylammonium bromide (CTAB) and p-(1,1,3,3-tetramethylbutyl) phenoxypoly(ethylene glycol), Triton X-100 (TX100) mixtures on polytetrafluoroethylene (PTFE). The obtained results indicate that the wettability of PTFE depends on the concentration and composition of the surfactants mixture. There is a minimum of the dependence between contact angle and composition of the mixtures for PTFE for each concentration at a monomer mole fraction of CTAB, α, equal 0.2, which points to the synergism in the wettability of PTFE. In contrast to Zisman, there is no linear dependence between cos θ and the surface tension of aqueous solution of CTAB and TX100 mixtures for all studied systems, but a linear dependence exists between the adhesional tension and surface tension for PTFE in the whole concentration range, the slope of which is −1, that suggests that the surface excess of the surfactant concentration at the PTFE–solution interface is the same as that at the solution–air interface for a given bulk concentration. It was also found that the work of adhesion of aqueous solution of surfactants to PTFE surface did not depend on the type of surfactant and its concentration. It means that the interactions across PTFE–solution interface were constant for the systems studied, and they were largely Lifshitz–van de Waals type. On the basis of the surface tension of PTFE and the Young equation and thermodynamic analysis of the adhesion work of aqueous solution of surfactant to the polymer surface it was found that in the case of PTFE the changes of the contact angle as a function of the mixture of nonionic and cationic surfactants concentration resulted only from changes of the polar component of solution surface tension.
Keywords: Polytetrafluoroethylene; Cetyltrimethylammonium bromide; Triton X-100; Wettability; Adhesion work; Contact angle;

The effect of the layer structure on the activity of immobilized enzymes in ultrathin films by Luciano Caseli; David S. dos Santos; Mauricio Foschini; Débora Gonçalves; Osvaldo N. Oliveira (326-331).
The molecular engineering capability of the layer-by-layer (LbL) method for fabricating thin films has been exploited in order to immobilize glucose oxidase (GOD) in films with alternating layers of chitosan. Chitosan was proven a good scaffolding material, as GOD molecules preserved their catalytic activity towards glucose oxidation. Using electrochemical measurements, we showed that chitosan/GOD LbL films can be used to detect glucose with a limit of detection of 0.2 mmol l−1 and an activity of 40.5 μA mmol−1 L μg−1, which is highly sensitive when compared to other sensors in previous reports in the literature. The highest sensitivity of the LbL film was achieved when only the top layer contained GOD, thus indicating that GOD in inner layers did not contribute to glucose oxidation, probably because it hampers analyte diffusion and electron transport through the deposited layers. This may be explained by the dense packing of GOD molecules in the LbL films with chitosan, as inferred from estimates of the amount of GOD adsorbed per layer using a quartz crystal microbalance.
Keywords: Layer-by-layer; Enzyme; Glucose oxidase; Catalytic activity;

by Arthur Hubbard (332).