Journal of Colloid And Interface Science (v.334, #1)

Elastic layer-structured metal organic frameworks (ELMs) by Hirofumi Kanoh; Atsushi Kondo; Hiroshi Noguchi; Hiroshi Kajiro; Aya Tohdoh; Yoshiyuki Hattori; Wei-Chun Xu; Mamoru Inoue; Tsutomu Sugiura; Kazuhiro Morita; Hideki Tanaka; Tomonori Ohba; Katsumi Kaneko (1-7).
Elastic layer-structured MOFs (ELMs) have a novel feature of a flexible structure and a reversible expansion/shrinkage behavior and usefulness in applicability to CO2 separation and CH4 storage.Elastic layer-structured metal organic frameworks (ELMs) having flexible two-dimensional structure show a gate phenomenon in sorption/desorption of simple gas molecules. The gate phenomenon is accompanied by expansion/shrinkage of the layers. The gas sorption/desorption is not based on a physical adsorption, but on a chemical reaction, which includes high cooperativity. The cooperative reaction could be analyzed thermodynamically. The gate phenomenon showed advantages in separation of CO2 from mixed gases and in storage of CH4 owing to easy release of absorbed molecules.
Keywords: Metal organic framework (MOF); Clathrate; CO2 separation; CH4 storage;

ZnO colloids initiated copolymerization of N-vinylcarbazole (NVK) and methyl acrylate (MA). A nanocomposite consisting of the ZnO nanocrystals and copolymer was obtained.This study designs a polymerization, in which ZnO colloids are used to initiate a copolymerization of N-vinylcarbazole and methyl acrylate, to synthesize functional composites for fabricating photoelectric devices. It is proved that a block copolymer is synthesized and a nanocomposite consisting of the ZnO and copolymer is obtained simultaneously. As a result, the ZnO nanocrystals are finely dispersed in the polymer matrix. A film-device is prepared from the obtained nanocomposite which has good film-forming ability and measured about photocurrents under illumination.
Keywords: PVK; ZnO nanocrystals; Nanocrystals-initiated polymerization; Copolymer; Nanocomposite; Photoconductive; One-step synthesis;

A novel dispersion polymerization system, with a polymerizable dimethylaminomethacrylate methyl chloride as stabilizer was developed. Much lower amount of stabilizer (0.025 wt%) was required to prepare monodisperse, stable and cation-charged PS particles.A novel dispersion polymerization system, with a methanol/water (MeOH/H2O) mixture as reaction medium and a polymerizable dimethylaminomethacrylate methyl chloride (DMC) as stabilizer was developed. By monitoring the polymerization evolution and observing the morphological changes of the polystyrene (PS) particles by SEM, it was found that this system had the following unique features: (1) a much lower amount of DMC (0.025 mass% based on styrene as opposed to 5 mass% for a routine system) was required to prepare monodisperse and stable PS particles; (2) the rate of polymerization was fast and the conversion was very high; (3) the monodisperse particles with average diameters of approximately 200–1600 nm could be directly obtained. These features were explained by a synergistic interaction between water and the quarternary ammonium cations. Combined with XPS, ion-exchange/conductometric titration, FTIR and 1H NMR analysis, a plausible polymerization mechanism through which the particles were stabilized by the PS-PDMC copolymer formed in situ was proposed.
Keywords: Dispersion polymerization; Cation charged; Polystyrene; Microspheres;

Uniform discotic wax particles via electrospray emulsification by Andres F. Mejia; Peng He; Dawei Luo; Manuel Marquez; Zhengdong Cheng (22-28).
We present a novel colloidal discotic system: the formation and self-assembling of wax microdisks with a narrow size distribution. Uniform wax emulsions are first fabricated by electrospraying of melt α-eicosene. The size of the emulsions can be flexibly tailored by varying the flow rate of the discontinuous phase, its electric conductivity, and the applied voltage. The process of entrainment of wax droplets, vital for obtaining uniform emulsions, is facilitated by the reduction of air–water surface tension and the density of the continuous phase. Then uniform wax discotic particles are produced via phase transition, during which the formation of a layered structure of the rotator phase of wax converts the droplets, one by one, into oblate particles. The time span for the conversion from spherical emulsions to disk particles is linearly dependent on the size of droplets in the emulsion, indicating the growth of a rotator phase from surface to the center is the limiting step in the shape transition. Using polarized light microscopy, the self-assembling of wax disks is observed by increasing disk concentration and inducing depletion attraction among disks, where several phases, such as isotropic, condensed, columnar stacking, and self-assembly of columnar rods are present sequentially during solvent evaporation of a suspension drop.
Keywords: Colloidal disks; Rods; α-Eicosene; Phase transition; Electrospray; Density match; Surface tension match;

Microwave-assisted polyol synthesis of aluminium- and indium-doped ZnO nanocrystals by Elin Hammarberg; Anna Prodi-Schwab; Claus Feldmann (29-36).
Non-agglomerated and redispersible ZnO:Al (AZO) and ZnO:In (IZO) are prepared via a polyol-mediated synthesis as nanoscale transparent conductive oxides. Chemical, electrical and optical properties are investigated in detail.Microwave heating is applied to prepare suspensions of ZnO:In (IZO) and ZnO:Al (AZO) nanocrystals in diethylene glycol as a high-boiling multidentate alcohol (so-called polyol). Both n-doped zinc oxides are realized with high yields and in suspensions with solid contents up to 10 wt-%. These suspensions are colloidally stable for months. According to dynamic light scattering, scanning electron microscopy, transmission electron microscopy, X-ray diffraction patterns and Brunauer–Emmett–Teller analysis as-prepared particles turn out to be single crystalline with an average diameter of 10–15 nm, a near monodisperse size distribution, and a low degree of agglomeration. As-prepared samples exhibit high resistivities due to the adhesion of DEG as a stabilizer on the particle surface. Subsequent to specific thermal post-treatment resistivities of 2.0 × 10−1 and 5.7 × 10−1  Ωcm are obtained for IZO and AZO powders, respectively. As a proof of the concept, thin layers are deposited on glass plates using a simple solvent evaporation technique. Post-treated layers exhibit a visible transmittance of about 80% and resistivities of 2.1 × 10−1  Ωcm (IZO) and 2.6 × 10−1  Ωcm (AZO). The bandgap of post-treated powders and thin layers is calculated to 3.2 and 3.3 eV, respectively.
Keywords: Polyol; Synthesis; Transparent conductive oxides; Zinc oxide; Nanomaterial;

Comparative structure analysis of non-polar organic ferrofluids stabilized by saturated mono-carboxylic acids by M.V. Avdeev; D. Bica; L. Vékás; V.L. Aksenov; A.V. Feoktystov; O. Marinica; L. Rosta; V.M. Garamus; R. Willumeit (37-41).
Magnetization analysis and SANS show a difference in stabilized magnetite size between new types of ferrofluids (stabilization by LA, MA, PA, SA) and classical sample (stabilization by OA).The structure of ferrofluids (magnetite in decahydronaphtalene) stabilized with saturated mono-carboxylic acids of different chain lengths (lauric, myristic, palmitic and stearic acids) is studied by means of magnetization analysis and small-angle neutron scattering. It is shown that in case of saturated acid surfactants, magnetite nanoparticles are dispersed in the carrier approximately with the same size distribution whose mean value and width are significantly less as compared to the classical stabilization with non-saturated oleic acid. The found thickness of the surfactant shell around magnetite is analyzed with respect to stabilizing properties of mono-carboxylic acids.
Keywords: Magnetic fluids; Magnetic nanoparticles; Magnetite; Mono-carboxylic acids; Fatty acids; Stabilization;

Synthesis of acrylic copolymers consisting of multiple amine pendants for dispersing pigment by Yu-Min Chen; Ru-Siou Hsu; Hsiao-Chu Lin; Shinn-Jen Chang; Shih-Chun Chen; Jiang-Jen Lin (42-49).
A new copolymer is effective for pigment dispersion in organic medium, which can be cured into film and directly observed for the pigment shape and size distribution.A class of acrylic copolymers with narrow molecular weight distribution from butyl methacrylate and glycidyl methacrylate comonomers via atom transfer radical polymerization was synthesized. Various types of polarities including hydroxyl-amines, glycols, and carboxylic acids were then grafted onto the oxirane side groups. The resultant comb-like copolymers with different polar pendants were tested for homogenizing a representative Yellow pigment in 1,6-hexanediol diacrylate medium. Specifically, the polyacrylates with 1,3-diamine pendants (7–10 multiplicity on each polymer strain) enabled to homogeneously disperse the pigment than the analogous copolymers with hydroxyl or carboxylic acid groups. Ultimately, the pigment dispersion with an average size of ca. 20 nm in diameter, high transmittance and low viscosity was achieved. Furthermore, the pigment dispersion was allowed to UV-cure into a film, and for the first time, the primary structures of the pigment particles (ca. 50 nm in diameter) were observed by transmission electronic microscope.
Keywords: ATRP; Acrylic copolymer; Dispersion; Pigment; UV-cured; Nanoparticles;

Novel TEG supported Cu–Ni bimetallic catalyst was synthesized and utilized in the direct synthesis of DMC to illustrate the superior properties of TEG as a catalyst support.Novel Cu–Ni bimetallic catalysts supported on thermally expanded graphite (TEG) were prepared as an example to show the particular characteristics of TEG as a carbon support material. The structures of TEG and the synthesized Cu–Ni/TEG catalysts were characterized using BET, FTIR, TG, SEM, TEM, XRD and TPR techniques. The catalytic activities of the prepared catalysts were investigated by performing micro-reaction in the direct synthesis of dimethyl carbonate (DMC) from CH3OH and CO2. The experimental results indicated that the prepared Cu–Ni/TEG catalysts exhibited highly catalytic activity. Under the optimal catalytic conditions at 100 °C and under 1.2 MPa, the highest conversion of CH3OH of 4.97% and high selectivity of DMC of 89.3% can be achieved. The highly catalytic activity of Cu–Ni/TEG in DMC synthesis can be attributed to the synergetic effects of metal Cu, Ni and Cu–Ni alloy in the activation of CH3OH and CO2 and the particular characteristics of TEG as a carbon support material.
Keywords: Thermally expanded graphite (TEG); Support; Bimetallic catalyst; Dimethyl carbonate; Catalysis;

Hydrothermal preparation and photocatalytic activity of mesoporous Au–TiO2 nanocomposite microspheres by Jiaguo Yu; Lin Yue; Shengwei Liu; Baibiao Huang; Xiaoyang Zhang (58-64).
Mesoporous Au–TiO2 nanocomposite microspheres were prepared by a simple hydrothermal method and their photocatalytic activity was obviously higher than that of pure TiO2 microspheres and Degussa P25.Au–TiO2 nanocomposite microspheres were prepared by hydrothermal treatment of precipitates of tetrabutyl titanate (Ti(OC4H9)4) in a mixed solution of water, ethanol and Au colloid particles at 180 °C for 7 h. The as-prepared products were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, nitrogen sorption, UV–visible diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy and photoluminescence spectroscopy. The photocatalytic activity was evaluated by photocatalytic oxidation decomposition of formaldehyde in air. The results showed that the presence of nanosized Au particles slightly depressed the grain growth of anatase, resulting in smaller crystallite size and greater specific surface areas. Moreover, the absorbance and photoluminescence of anatase TiO2 was modified by those added Au nanoparticles and an appropriate Au amount in Au–TiO2 nanocomposite microspheres led to increase of band gap, decrease of photoluminescence intensity and prolongation of life of photo-generated electrons and holes. The photocatalytic activity of Au–TiO2 nanocomposite microspheres was obviously higher than that of pure TiO2 microspheres and Degussa P25. When the atomic percentage ratio of Au to Ti was below 0.00425, the apparent reaction rate constants increased. When the atomic percentage ratio of Au to Ti reached 0.00425, the sample displayed the highest photocatalytic activity.
Keywords: TiO2; Au; Nanocomposite; Microspheres; Photocatalytic activity;

Simulation and experimental study of intercalation of urea in kaolinite by Gábor Rutkai; Éva Makó; Tamás Kristóf (65-69).
Representative simulation snapshots of the kaolinite/urea intercalate taken at the identified stable basal spacings.Experimental measurements and molecular simulations were used to describe the characteristics of the kaolinite/urea intercalation compound. The intercalation compound was synthesized by a mechanochemical method and examined by X-ray diffraction and thermogravimetry. Additionally, a series of NpT (constant particle number–pressure–temperature) simulations was performed to identify thermodynamically stable basal spacings. From the simulations the most probable molecular orientations were determined for single and double layered arrangements of urea molecules that develop between the layers of kaolinite.
Keywords: Kaolinite; Intercalation; Urea; Molecular simulation; Mechanochemical treatment;

Drops impacting inclined fibers by Keyvan Piroird; Christophe Clanet; Élise Lorenceau; David Quéré (70-74).
Drop impacting an inclined fiber. Although the impact speed is too high to fully stop the drop, the fiber inclination generates a partial capture of the impacting liquid.Mats of fibers are often used to capture liquid drops, such as in filters or in fog’s nets. It is desired to optimize the efficiency of capture, in particular in the limit of drops larger than the fibers, for which filters remain highly permeable. Here we show that the efficiency of capture is dramatically increased by tilting the fibers: then, the velocity V * below which a drop is fully captured is made much larger; moreover, the tilt maximizes the liquid volume left on the fiber when the impact velocity exceeds V *.
Keywords: Impact; Wetting; Filtration; Fibers; Drops;

Effect of surfactant surface coverage on formation of solid lipid nanoparticles (SLN) by T. Helgason; T.S. Awad; K. Kristbergsson; D.J. McClements; J. Weiss (75-81).
Particle size changes in tripalmitin emulsions cooled to 10 °C to induce formation of solid lipid nanoparticles (SLN) as a function of surfactant surface coverage. At sufficiently high surface coverage, particles remain un-aggregated. At low surface coverage, particles have substantially different crystal structures resulting in rapid aggregation.The effect of surfactant surface coverage on formation and stability of Tween 20 stabilized tripalmitin solid lipid nanoparticles (SLN) was investigated. A lipid phase (10% w/w tripalmitin) and an aqueous phase (2% w/w Tween 20, 10 mM phosphate buffer, pH 7) were heated to 75 °C and then homogenized using a microfluidizer. The resulting oil-in-water emulsion was kept at a temperature (37 °C) above the crystallization temperature of the tripalmitin to prevent solidification of emulsion droplets, and additional surfactant at various concentrations (0–5% w/w Tween 20) was added. Droplets were then cooled to 5 °C to initiate crystallization and stored at 20 °C for 24 h. Particle size and/or aggregation were examined visually and by light scattering, and crystallization behavior was examined by differential scanning calorimetry (DSC). Excess Tween 20 concentration remaining in the aqueous phase was measured by surface tensiometry. Emulsion droplets after homogenization had a mean particle diameter of 134.1 ± 2.0 nm and a polydispersity index of 0.08 ± 0.01. After cooling to 5 °C at low Tween 20 concentrations, SLN dispersions rapidly gelled due to aggregation of particles driven by hydrophobic attraction between insufficiently covered lipid crystal surfaces. Upon addition of 1–5% w/w Tween 20, SLN dispersions became increasingly stable. At low added Tween 20 concentration (<1% w/w) the SLN formed gels but only increased slightly at higher surfactant concentrations (>1% w/w). The Tween 20 concentration in the aqueous phase decreased after tripalmitin crystallization suggesting additional surfactant adsorption onto solid surfaces. At higher Tween 20 concentrations, SLN had increasingly complex crystal structures as evidenced by the appearance of additional thermal transition peaks in the DSC. The results suggest that surfactant coverage at the interface may influence crystal structure and stability of solid lipid nanoparticles via surface-mediated crystal growth.
Keywords: Gelation; Solid lipid nanoparticles; Surfactants; Crystallization;

Ripening of a draining foam bubble by N. Louvet; F. Rouyer; O. Pitois (82-86).
Influence of films swelling under drainage condition on the ripening of a foam bubble.A forced Ostwald ripening experiment is performed on a single foam bubble. The bubble size is followed as the system is wetted with a constant liquid flow rate delivered from one of the bubble Plateau borders. Obtained ripening velocities cannot be described with a model based on a constant film thickness assumption. Within these well-controlled experimental conditions, the film thickness is measured and found to depend on the imposed liquid flow rate. It is shown that the bubble growth rate is well predicted as the films thickness evolution is explicitly introduced in the ripening model. Finally, it is suggested that existing results for the coarsening of draining foams could be understood following the approach validated on the bubble scale.
Keywords: Drainage; Bubble; Film permeability; Coarsening; Foam; Plateau border;

Biocompatible microemulsions of dicephalic aldonamide-type surfactants: Formulation, structure and temperature influence by Kazimiera A. Wilk; Katarzyna Zielińska; Agnieszka Hamerska-Dudra; Adam Jezierski (87-95).
Pseudoternary phase diagrams of N-dodecyl-N,N-bis[(3-d-aldonylamido)propyl]amines C12-DX (gluconyl GA or lactobionyl LA)/iso-butanol/hydrophilic (diethylene glycol monoethyl ether DGME) or hydrophobic (iso-octane) oils/water were studied at 25, 40, 55 °C by EPR and DLS.The temperature effects upon microemulsion systems composed of dicephalic N-dodecyl-N,N-bis[(3-d-aldonylamido)propyl]amines C12-DX (gluconyl GA or lactobionyl LA)/iso-butanol/hydrophilic (diethylene glycol monoethyl ether) or hydrophobic (iso-octane) oils/water were investigated by evaluating isotropic area magnitudes in the pseudoternary phase diagrams, as well as droplet characteristics by electron paramagnetic resonance (EPR) and dynamic light scattering (DLS) spectroscopies at 25, 40 and 55 °C. We concluded that in the examined systems a cosurfactant, such as middle-chain alcohol, was needed to obtain large mesophase isotropic areas. The phase behavior and structure of the examined systems were temperature insensitive but they were intimately determined by the nature of the C12-DX and the polarity of the oil phase. By adjusting the nature of the oil, as well as the surfactant hydrophilicity, the performed isotropic systems containing low amounts of nonaggressive surfactant could be formulated successfully. Interfacial properties and the dynamic structure of the surfactant/cosurfactant monolayer were studied by the spin probe technique using the 16-doxylstearic acid methyl ester (16-DSE) as the appropriate probe. The polarity of the interface was not affected by temperature but the interface rigidity was dependent upon the nature of the surfactant and oil as well as on temperature. The size of the dispersed domains, evaluated by dynamic light scattering (DLS), was found to be a function of temperature, surfactant content and type of additives. The investigated o/w microemulsions (i.e., ranging from 3.0 to 8.8 nm) constituted promising templates for a variety of syntheses of nanostructures with small size and high-capacity solubilizing media.
Keywords: o/w and w/o microemulsions; Temperature-insensitive phase diagram; Nonionic saccharide surfactants; EPR;

Transport of carboxymethyl cellulose stabilized ZVI nanoparticles in four porous media was investigated and interpreted via classical CDE and filtration theory.Carboxymethyl cellulose (CMC) can facilitate in situ delivery of zero-valent iron (ZVI) nanoparticles in contaminated aquifer. This work investigated transport of CMC-stabilized ZVI nanoparticles (CMC-Fe) using column breakthrough experiments and model simulations. The nanoparticles (18.1 ± 2.5 nm) were transportable through four saturated model porous media: coarse and fine glass beads, clean sand, and sandy soil. The transport data were interpreted using both classical filtration theory and a modified convection–dispersion equation with a first-order removal rate law. At full breakthrough, a constant concentration plateau (C e /C 0) was reached, ranging from 0.99 for the glass beads to 0.69 for the soil. While Brownian diffusion was the predominant mechanism for particle removal in all cases, gravitational sedimentation also played an important role, accounting for 30% of the overall single-collector contact efficiency for the coarse glass beads and 6.7% for the soil. The attachment efficiency for CMC-Fe was found to be 1–2 orders of magnitude lower than reported for ZVI nanoparticles stabilized with other commercial polymers. The particle removal and travel distance are strongly dependent on interstitial flow velocity, but only modestly affected by up to 40 mM of calcium. Simulation results indicate that once delivered, 99% of the nanoparticles will be removed by the soil matrix within 16 cm at a groundwater flow velocity of 0.1 m/day, but may travel over 146 m at flow velocity of 61 m/day.
Keywords: Chlorinated solvents; Fate and transport; Groundwater remediation; Nanoparticle; Zero-valent iron; ZVI;

A cauliflower-like gold structure for superhydrophobicity by Hong-Xuan Ren; Xing-Jiu Huang; Oktay Yarimaga; Yang-Kyu Choi; Ning Gu (103-107).
A hierarchical cauliflower-like structure was produced by a two-step route that involves RSA process and electrochemical growth for superhydrophobicity.We present a two-step route to produce a hierarchical cauliflower-like gold structure that involves the adsorption of gold nanoparticles described by the random sequential adsorption (RSA) model, followed by the electrochemical growth on the surfaces of the primary gold nanoparicles. The structure was confirmed using scanning electron microscopy (SEM), energy dispersive spectrometer analysis (EDS), and X-ray diffraction (XRD). After fluoroalkylsilane modification, the cauliflower-like structured surface exhibits a high contact angle and a low sliding angle.
Keywords: Superhydrophobic; Electrodeposition; RSA; Cauliflower-like structure;

Facile synthesis of polyaniline “sunflowers” with arrays of oriented nanorods by Taoqing Wang; Wenbin Zhong; Xutao Ning; Yongxin Wang; Wantai Yang (108-112).
Polyaniline (PANI) “sunflowers” made of arrays of oriented nanorods were synthesized by chemical oxidative polymerization of aniline in the presence of cetyltrimethylammonium bromide (CTAB).Polyaniline (PANI) “sunflowers” made of arrays of oriented nanorods were synthesized by chemical oxidative polymerization of aniline in the presence of cetyltrimethylammonium bromide (CTAB) and suitable concentration of HNO3 at about 0 °C (ice bath). The reaction conditions, such as the concentration of reagents and reaction temperature were systematically investigated and controlled on the preparation of PANI “sunflowers”. The results also suggest that HNO3 probably plays a key role in forming PANI “sunflowers”. A possible forming mechanism of the PANI nanostructures is offered.
Keywords: Polyaniline; Oriented arrays; Nanorods; Cetyltrimethylammonium bromide (CTAB); Hierarchical nanostructures;