Journal of Colloid And Interface Science (v.345, #1)

Cover 1 (OFC).

Ionic liquids, ILs, carrying long-chain alkyl groups are surface active, SAILs. We investigated the micellar properties of the SAIL 1-hexadecyl-3-methylimidazolium chloride, C16MeImCl, and compared the data with 1-hexadecylpyridinium chloride, C16PyCl, and benzyl (3-hexadecanoylaminoethyl)dimethylammonium chloride, C15AEtBzMe2Cl. The properties compared include critical micelle concentration, cmc; thermodynamic parameters of micellization; empirical polarity and water concentrations in the interfacial regions. In the temperature range from 15 to 75 °C, the order of cmc in H2O and in D2O is C16PyCl > C16MeImCl > C15AEtBzMe2Cl. The enthalpies of micellization, Δ H mic ° , were calculated indirectly from by use of the van’t Hoff treatment; directly by isothermal titration calorimetry, ITC. Calculation of the degree of counter-ion dissociation, α mic, from conductivity measurements, by use of Evans equation requires knowledge of the aggregation numbers, N agg, at different temperatures. We have introduced a reliable method for carrying out this calculation, based on the volume and length of the monomer, and the dependence of N agg on temperature. The N agg calculated for C16PyCl and C16MeImCl were corroborated by light scattering measurements. Conductivity- and ITC-based Δ H mic ° do not agree; reasons for this discrepancy are discussed. Micelle formation is entropy driven: at all studied temperatures for C16MeImCl; only up to 65 °C for C16PyCl; and up to 55 °C for C15AEtBzMe2Cl. All these data can be rationalized by considering hydrogen-bonding between the head-ions of the monomers in the micellar aggregate. The empirical polarities and concentrations of interfacial water were found to be independent of the nature of the head-group.
Keywords: Surface active ionic liquids; Conductivity of cationic micelles; Isothermal titration calorimetry of cationic micelles; Light scattering; Polarity of interfacial water; 1-Hexadecyl-3-methylimidazolium chloride; 1-Hexadecylpyridinium chloride; Benzyl (3-hexadecanoyl-aminoethyl)dimethylammonium chloride;

Adsorption of Pd(II) complexes from chloride solutions obtained by leaching chlorinated spent automotive catalysts on ion exchange resin Diaion WA21J by Shaobo Shen; Tonglin Pan; Xinqiang Liu; Lei Yuan; Yongjian Zhang; Jinchao Wang; Zhanchen Guo (12-18).
Based on DKR isotherm, the apparent adsorption energies for Pd(II) were between −15.43 and −23.57 kJ/mol at 18–40 °C. Thus, chemical adsorption was main adsorption mechanism.It was found that Rh, Pd and Pt contained in the spent ceramic automotive catalysts could be effectively extracted by dry chlorination with chlorine. In order to concentrate Pd(II) contained in the chloride solution obtained from the dry chlorination process, thermodynamic and kinetics studies for adsorption of Pd(II) complexes from the chloride solutions on anionic exchange resin Diaion WA21J were carried out. It was found that Pd, Pt, Rh, Al, Fe, Si, Zn and Pb from the chloride solution could be adsorbed on the resin. The isothermal adsorption of Pd(II) was found to fit Freundlich, Langmuir and Dubinin–Kaganer–Radushkevich models under the adsorption conditions. The adsorption of Pd(II) on the resin was favorable according to the values of 1/n and RL from Freundlich and Langmuir adsorption isotherms, respectively. The maximum monolayer adsorption capacities Q max based on Langmuir adsorption isotherms were 5.70, 4.84 and 4.05 mg/g and the corresponding value Xm based on Dubinin–Kaganer–Radushkevich were 5.55, 4.69 and 4.01 mg/g at temperatures 18 °C, 28 °C and 40 °C, respectively. The apparent adsorption energies (Ead ) based on Dubinin–Kaganer–Radushkevich isotherm were −15.43, −16.22 and −23.57 kJ/mol for the temperatures 18 °C, 28 °C and 40 °C, respectively. Chemical adsorption was a main mechanism involved in the adsorption process. Pd(II) adsorption on the resin could be accelerated by increasing the adsorption temperature. The adsorption of Pd(II) from the chloride solution on the resin underwent pseudo-first order kinetic process and the apparent adsorption activation energy Ea was 15.0 kJ/mol. The intra-particle diffusion was a main rate controlling step in the Pd(II) adsorption process under the adsorption conditions.
Keywords: Adsorption; Pd(II); Chloride solution; Ion exchange resin; Diaion WA21J; Adsorption thermodynamics; Adsorption kinetics;

The disorder region of self-assembled monolayers after indentation at high temperature is larger than that at low temperature.The interface and nanoindentation mechanisms of alkanethiol self-assembled monolayers (SAMs) chemisorbed on a gold surface are investigated using molecular dynamics simulation. The mechanisms include the nanoindentation depths, the workpiece temperatures, the numbers of SAM layers, the length of united-atoms per chain, and the shapes of the indenters. The simulation results show that the disorder and the plastic mobility of SAM chains increased with increasing indentation depth. The relaxation force and the plastic energy almost linearly increased with increasing indentation depth. The disorder region after indentation at high temperature is larger than that at low temperature. The adhesive force shows a dependence on temperature during indentation. The potential energy decreases with increasing number of SAM layers. The structural morphologies of the SAMs were not affected at the third layers for SAM film with four layers. The maximum load quickly decreases for film with two SAM layers. The structures of the SAM can be easily tilted and bent when the united-atoms per chain length is long. The SAM atoms become more disorderly and the elastic recovery is smaller when the SAM length of the united-atoms per chain is long after indentation.
Keywords: Nanoindentation; Self-assembled monolayers; Molecular dynamics; Size effect; Thermal effect;

Preparation of Span 80/oil/water highly concentrated emulsions: Influence of composition and formation variables and scale-up by Mabel Capdevila; Alicia Maestro; Montserrat Porras; José M. Gutiérrez (27-33).
Diameter of HIPRE droplets depends not only on surfactant–oil ratio, SO, but also on mixing rate, ω, and an interaction of both formulation and preparation variables is observed.The influence of composition and preparation variables on the properties of W/O highly concentrated emulsions obtained in the system Span 80/oil/water was studied. Emulsions prepared with decane, dodecane and hexadecane were analysed. Stability of emulsions was found to depend on the oil as follows: stability of hexadecane emulsions > dodecane > decane. It was attributed to the lower solubility of water in the oil with longer chain. Experimental design tools were used to study the influence of composition and preparation variables and scale-up on the droplet size and polydispersity of emulsions formed. The most important factor was found to be the surfactant–oil ratio, SO, as more surfactant could stabilize more interface, but other preparation variables, like mixing rate, ω, were also found to influence the droplet size and polydispersity. The proper scale-up variables were found not to correspond to the dimensionless variables commonly used in scale-up studies, but total addition time, tt , and angular mixing velocity, ω, seemed to be the proper ones.
Keywords: Highly concentrated emulsion; HIPRE; Scale-up; Experimental design;

Smectite flocculation structure modified by Al13 macro-molecules – As revealed by the transmission X-ray microscopy (TXM) by Marek S. Żbik; Wayde N. Martens; Ray L. Frost; Yen-Fang Song; Yi-Ming Chen; Jian-Hua Chen (34-40).
TEM micrographs of Ca2+ smectite flakes shown significant roughness at the platelet surface 200 nm extended in the Na+ and ∼50 nm in Ca2+ exchangeable forms.The aggregate structure which occurs in aqueous smectitic suspensions is responsible for poor water clarification, difficulties in sludge dewatering and the unusual rheological behaviour of smectite rich soils. These macroscopic properties are dictated by the 3D structural arrangement of smectite finest fraction within flocculated aggregates. Here, we report results from a relatively new technique, transmission X-ray microscopy (TXM), which makes it possible to investigate the internal structure and 3D tomographic reconstruction of the smectite clay aggregates modified by Al13 Keggin macro-molecule [Al13(O)4(OH)24(H2O)12]7+. Three different treatment methods were shown resulted in three different micro-structural environments of the resulting flocculation. In case of smectite sample prepared in Methods 1 and 3 particles fall into the primary minimum where Van der Waals forces act between FF oriented smectite flakes and aggregates become approach irreversible flocculation. In case of sample prepared using Method 2, particles contacting by edges (EE) and edge to face (EF) orientation fell into secondary minimum and weak flocculation resulted in severe gelation and formation of the micelle-like texture in fringe superstructure, which was first time observed in smectite based gel.
Keywords: Transmission X-ray microscopy; Keggin flocculation; Smectite gelation; Gel;

ZnO nanoparticle-containing emulsions for transparent, hydrophobic UV-absorbent films by Britta Tigges; Martin Möller; Oliver Weichold (41-45).
The preparation of highly transparent, multifunctional coatings exhibiting both water repellency and UV protection from aqueous, mixed emulsions containing zinc oxide nanoparticles is presented.A simple method for the preparation of thin, zinc oxide nanoparticle-containing films showing high UV absorption, high transmittance in the visible range (>88%), and water repellence with contact angles of 120° is presented. The films are coated from an emulsion containing the hydrophobic polymer and the nanoparticles. This emulsion was prepared by mixing commercial o/w emulsions used for hydrophobic coatings on textiles with ZnO nanoparticle-containing o/w emulsions. The latter were designed so that the mixed coating formulation could be prepared without breaking. Preparation and properties of the o/w emulsions as well as the final films are elaborated. The performance of hydrophobic and hydrophilic ZnO nanoparticles during preparation and in the final film is evaluated.
Keywords: ZnO nanoparticles; UV-absorbent films; Emulsions; Water repellency; Transparent films;

The plasticized zein films prepared from aqueous dispersion (pseudolatex) are compact, smooth and can be used for moisture resistant film coating of sustained-release tablets containing very water soluble drug.Zein is an alcohol soluble protein of corn origin that exhibits hydrophobic properties. Pseudolatexes are colloidal dispersions containing spherical solid or semisolid particles less than 1 μm in diameter and can be prepared from any existing thermoplastic water-insoluble polymer. The novel plasticized film-coating pseudolatex of zein was studied in formulation of sustained-release tablets containing very water-soluble drug. Film formation of plasticized aqueous dispersion was compared with film forming properties of plasticized organic solvent system (ethanol) of zein. The water vapor permeability (WVP), water uptake and erosion, and moisture sorption were evaluated with free films. The tablets containing metoprolol tartrate as a model drug were used in pan-coating experiments. Aqueous film coatings plasticized with PEG 400 exhibited very low water uptake. No significant difference in WVP, moisture sorption and erosion were found between aqueous films and organic solvent-based films of zein plasticized with PEG 400. The atomic force microscopy (AFM) images on microstructure of films showed that colloidal particle size of zein in the aqueous films was smaller than that observed in the solvent-based films. In addition, the aqueous-based films were more compact and smoother than the respective solvent-based films. The aqueous zein-coated tablets containing very water-soluble drug (metoprolol tartrate) exhibited clear sustained-release dissolution profiles in vitro, while the respective solvent-based film-coated tablets showed much faster drug release. Furthermore, aqueous zein-coated tablets had lower water absorption at high humidity conditions. In conclusion, the plasticized aqueous dispersion (pseudolatex) of zein can be used for moisture resistant film coating of sustained-release tablets containing very water-soluble drug.
Keywords: Zein; Aqueous film-coating; Pseudolatex; Film formation; Very water-soluble drug; Sustained release tablet;

Self-similar assemblies of globular whey proteins at the air–water interface: Effect of the structure by Najet Mahmoudi; Cédric Gaillard; François Boué; Monique A.V. Axelos; Alain Riaublanc (54-63).
Whey globular proteins self-assemble in fractal aggregates with density structure depending on the electrostatic interactions. When spread at the air–water interface, these aggregates show a power-law scaling behavior in the semi-dilute surface concentration regime, with an exponent ranging from 5 to 9 depending on the electrostatic interactions and the aggregation state.We investigated the structure of heat-induced assemblies of whey globular proteins using small angle neutron scattering (SANS), static and dynamic light scattering (SLS and DLS), and cryogenic transmission electron microscopy (Cryo-TEM). Whey protein molecules self-assemble in fractal aggregates with a structure density depending on the electrostatic interactions. We determined the static and dynamic properties of interfacial layer formed by the protein assemblies, upon adsorption and spreading at the air–water interface using surface film balance and interfacial dilatational rheology. Upon spreading, all whey protein systems show a power-law scaling behavior of the surface pressure versus concentration in the semi-dilute surface concentration regime, with an exponent ranging from 5.5 to 9 depending on the electrostatic interactions and the aggregation state. The dilatational modulus derived from surface pressure isotherms shows a main peak at 6–8 mN/m, generally considered to be the onset of a conformational change in the monolayer, and a second peak or a shoulder at 15 mN/m. Long-time adsorption kinetics give similar results for both the native whey proteins and the corresponding self-similar assemblies, with a systematic effect of the ionic strength.
Keywords: Whey globular proteins; Fractal aggregation; SANS; Cryo-TEM; Air–water interface; Interfacial rheology;

Conceptual scheme for the synthesis of functionalized core–shell iron–gold nanoparticles and assessment of magnetic properties and cell toxicity.Core–shell iron–gold (Fe@Au) nanoparticles were synthesized by a facile reverse micelle procedure and the effect of water to surfactant molar ratio (w) on the size, size distribution and magnetic properties of the nanoparticles was studied. MTT assay was utilized to evaluate the cell toxicity of the nanoparticles. To functionalize the particles for MRI imaging and targeted drug delivery, the particles were coated by polyglycerol through capping with thiol followed by polymerization of glycidol. The characteristics of the particles were examined by X-ray diffraction (XRD), transmission electron microscopy (TEM), vibrating sample magnetometere (VSM), UV–visible spectroscopy, and Fourier transform infrared spectroscopy (FT-IR). It was found that the size and size distribution of the nanoparticles increase by increasing the water to surfactant molar ratio (w). The particles were spherical in shape with a thin layer of gold. Complementary growth of the gold shell on the iron core was noticed. Meanwhile, two types of agglomeration including magnetic beads and magnetic colloidal nanocrystals clusters were observed dependent on the w-value. The magnetic measurement studies revealed the superparamagnetic behavior of the nanoparticles. MTT assay result indicated the synthesized nanoparticles are nontoxic that will be useful for biomedical applications.
Keywords: Superparamagnetic nanoparticles; Iron–gold; Cell toxicity; MTT assay; Polyglycerol;

Electrokinetic phenomena in wavy channels by Alexander E. Malevich; Vladimir V. Mityushev; Pierre M. Adler (72-87).
Electroosmotic flows are studied in wavy channels by expanding the solution into a double series for a binary dilute electrolyte.Electroosmotic flows are studied in wavy channels by expanding the solution into a double series in terms of the dimensionless amplitudes and of the dimensionless zeta potential for a binary dilute electrolyte. The expansion technique by means of formal calculations is described. Some examples are illustrated and discussed for two- and three-dimensional channels. The importance of the varicose or sinuous character of the channels as well as the role of high frequency roughness are demonstrated. These features may be used for practical purposes in order to amplify or diminish coupling effects in an algebraic way.
Keywords: Electroosmotic; Zeta potential; Rough channels; Formal expansion;

Calcium carbonate–hydrolyzed soy protein complexation in the presence of citric acid by Latha-Selvi Canabady-Rochelle; Christian Sanchez; Michel Mellema; Sylvie Banon (88-95).
The addition of soy proteins in a solution of calcium carbonate dissolved in citric acid induces calcium–soy protein complexation, preventing from CaCO3 recrystallisation.The influence of hydrolyzed soy proteins on calcium carbonate stabilization was studied in citric acid solution. Calcium–soy proteins interactions were characterized using a calcium ion selective electrode, turbidity, and Isothermal Titration Calorimetry. Once the meta-stable phase was reached or just after soy protein addition, spray-drying was performed and SEM, XRD, and XPS analysis were carried out on spray-dried powders. In citric acid solution calcite crystals were eroded giving rise to smaller amorphous particles. In the presence of soy proteins, complexation exothermic in nature occurred with the mineral phase, which prevented CaCO3 from recrystallisation and kept the system in an amorphous state. SEM performed on spray-dried powder showed that soy proteins were swollen in presence of mineral phase and resulted in a decrease of calcium concentration at the extreme surface of the studied powders as demonstrated by XPS.
Keywords: Calcium carbonate; Soy protein; Complexation; Amorphous phase; ITC; SEM; XPS;

Attenuated total reflectance Fourier transform infrared spectroscopy (ATr-FTIR) was applied to study the effect of calcium ions and sodium silicate on the adsorption of an anionic flotation collector on magnetite.Previous studies have shown that agglomeration of the magnetite concentrate after reverse flotation of apatite is negatively affected by the collector species adsorbed on the surface of magnetite. In this work, the effect of ionic strength, calcium ions and sodium silicate on the unwanted adsorption of a model anionic flotation collector on synthetic magnetite was studied in situ using attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). The amount of collector adsorbed was found to increase with increasing ionic strength at pH 8.5 providing evidence to the contribution of electrostatic forces to the adsorption of the collector. Adding sodium silicate to the system resulted in a threefold decrease in the amount of collector adsorbed compared to when no sodium silicate was added, confirming the depressing activity of sodium silicate on magnetite. Calcium ions were shown to increase the adsorption of both the collector and sodium silicate on magnetite. The depressing effect of sodium silicate on collector adsorption was completely suppressed in the presence of calcium ions under the conditions studied. Furthermore, the amount of collector adsorbed on magnetite from the silicate-collector solution increased 14 times upon addition of calcium ions suggesting that calcium ions in the process water may increase undesired adsorption of the collector on the iron oxide.
Keywords: Magnetite; Flotation collector; Calcium; Silicate; Adsorption; ATR-FTIR;

A fairly homogeneous Ag film was formed at the toluene–water interface by adding benzenethiol into poly(ethylenimine) (PEI)-stabilized Ag sol produced by heating a PEI-containing AgNO3 solution.A one-pot, size-controlled preparation of amine-functionalized silver nanoparticles is possible using poly(ethylenimine) (PEI) as a reducing and a stabilizing agent simultaneously. The PEI-stabilized Ag nanoparticles thus prepared in aqueous phase can further be assembled into 2-dimensional (2-D) arrays at the water–toluene interface by heating. By the addition of benzenethiol (BT) into the toluene, a more robust 2-D film is formed, not only at the interface but also on the inner surface of the sampling bottle. The latter Ag film can also be formed, through brief contact with the mixture, on glass slides and even on dielectric beads and cotton fabrics. These Ag-coated films are highly surface-enhanced Raman scattering (SERS) active and also exhibit a very intense SERS spectrum of 4-aminobenzenethiol (4-ABT) or 4-nitrobenzenethiol (4-NBT) via a place-exchange reaction that takes place between BT and 4-ABT or 4-NBT. In addition, the Ag-coated fabrics would be used as antibacterial gauzes for the treatment of burned skin and also as antistatic mats for the ready dissipation of electrical energy buildup. The present electroless deposition method of Ag is thus expected to serve as a technique in high demand in various fields.
Keywords: Silver nanoparticles; Poly(ethylenimine); Water–toluene interface; Surface-enhanced Raman scattering (SERS); 2-Dimensional film;

Exfoliation of α-hydroxides of nickel and cobalt in water by C. Nethravathi; B. Viswanath; Mency Sebastian; Michael Rajamathi (109-115).
p-Aminobenzote intercalated α-hydroxides of nickel and cobalt exfoliate in water when the pH of the medium is ∼7.p-Aminobenzoate ion intercalated α-hydroxides of nickel/cobalt were synthesized by precipitation using ammonia (pH = ∼12). Aqueous colloidal suspension of α-hydroxide of nickel/cobalt was obtained on washing the precipitate as the pH was reduced to ∼7. The development of partial positive charge on the amine end of the intercalated anion causes repulsion between the layers leading to exfoliation and colloidal suspension of monolayers in water. While the layers could be restacked from the colloidal suspension in the presence of other anions in the case of α-cobalt hydroxide, the exfoliation could not be reversed easily in the case of the nickel analog.
Keywords: α-Hydroxides of nickel/cobalt; Intercalation; Exfoliation;

Micro–nano hierarchically structured nylon 6,6 surfaces with unique wettability by Liang Zhang; Xiaoyan Zhang; Zhen Dai; Junjie Wu; Ning Zhao; Jian Xu (116-119).
Nylon 6,6 surface was covered with hierarchical particles after phase separation. The surface showed superhydrophilicity. After modification, a nearly conformal morphology was generated and the surface was superhydrophobicity.A micro–nano hierarchically structured nylon 6,6 surface was easily fabricated by phase separation. Nylon 6,6 plate was swelled by formic acid and then immersed in a coagulate bath to precipitate. Micro particles with nano protrusions were generated and linked together covering over the surface. After dried up, the as-formed surface showed superhydrophilic ability. Inspired by lotus only employing 2-tier structure and ordinary plant wax to maintain superhydrophobicity, paraffin wax, a low surface energy material, was used to modify the hierarchically structured nylon 6,6 surface. The resultant surface had water contact angle (CA) of 155.2 ± 1.3° and a low sliding angle. The whole process was carried on under ambient condition and only need a few minutes.
Keywords: Nylon; Phase separation; Polyamide; Superhydrophilic; Superhydrophobic;

Variations in mechanical and thermal properties of mesoporous alumina thin films due to porosity and ordered pore structure by Tae-Jung Ha; Hyung-Ho Park; Eul Son Kang; Sangwoo Shin; Hyung Hee Cho (120-124).
As well as porosity, pore structure has a great effect on mechanical strength and thermal conductivity. Ordered pore structure can enhance the mechanical and thermo-isolating properties of these mesoporous films.Ordered mesoporous aluminum oxide films with porosity ranging between 5% and 37% were synthesized by evaporation-induced self-assembly (EISA) using surfactant templating. To investigate the effects of mesoporous structure on thermal properties, changes in pore structure including pore size, pore distribution, and porosity were monitored as a function of surfactant concentration (Pluronic P-123, poly(ethylene oxide)20–poly(propylene oxide)70–poly(ethylene oxide)20). The ordered mesoporous alumina films were then examined to determine how their morphology influences their thermal properties. These alumina films had a body-centered cubic pore structure or a random-oriented pore structure, depending on the surfactant concentration used, and superior thermal properties were obtained by controlling porosity and pore structure. Therefore, the ordered mesoporous alumina films synthesized in this study can be used as high-temperature thermo-isolating materials.
Keywords: Mesoporous Al2O3 film; Pluronic P-123; Porosity; Ordered pore structure;

Synthesis and photocatalytic properties of hierarchical metal nanoparticles/ZnO thin films hetero nanostructures assisted by diblock copolymer inverse micellar nanotemplates by Yoon Hee Jang; Saji Thomas Kochuveedu; Min-Ah Cha; Yu Jin Jang; Ji Yong Lee; Jieun Lee; Juyon Lee; Jooyong Kim; Du Yeol Ryu; Dong Ha Kim (125-130).
Metal dot-on-ZnO thin film type hierarchical nanostructures with enhanced photocatalytic activities compared with pure ZnO thin films were fabricated based on sequential sol–gel chemistry and templating diblock copolymer inverse micelles.Metal dot-on-ZnO type hierarchical nanostructures composed of ordered arrays of noble metal nanoparticles with controlled areal density, prepared from poly(styrene-block-vinyl pyridine) diblock copolymer inverse micelles loaded with metal precursors, on sol–gel process based ∼48 nm thick ZnO thin films exhibit enhanced photocatalytic activities compared with pure ZnO thin films in terms of photodegradation of methylene blue.
Keywords: Hierarchical nanostructures; ZnO thin film; Self-assembly; Block copolymer micelle; Sol–gel;