научный журнал по химии Коллоидный журнал ISSN: 0023-2912

AHMAD RABIEE, HABIBOLLAH BAHARVAND, HAJAR JAMSHIDI — 2013 г.

Particle formation in polymerization of styrene induced within two stratified layers of a monomer and water containing an initiator was studied in the absence of emulsifiers and stirring. A polymerization-induced decrease of interfacial surface tension was observed. The particle size distribution was characterized by dynamic light scattering during polymerization. The results confirm particle nucleation through spontaneous emulsification process.

GENXIANG LUO, GUOZHI LIU — 2013 г.

In this paper, we suggest an analytical solution to Poisson–Boltzmann equation for the calculation of potential distributions between two identical plates with high constant surface potential. Our expression fits well to the exact values of the potential between two parallel plates. Numerical results indicate that this analytical solution provides accurate description for the dimensionless distance 2. The suggested solution can be successfully applied in calculating the potential for identical plates with high or moderate surface potentials. A simple analytical expression for the energy of interactions between two identical plates with constantly high surface potential is also given. The solutions in analytical, exact and numerical forms become indistinguishable when y0 3, x 4 and y0 = 2.0, x 3, respectively. When y0 = 2.0, x 1.2, the approximate solution is in close agreement with the exact solution.

FENG FU, LOU-JUN GAO, QING-BO WEI, YAN-LING LUO, YAN-WEI SONG — 2013 г.

Polyacrylamide grafted poly(vinyl alcohol)/polyvinylpyrrolidone (PAM-g-PVA/PVP) semi-interpenetrating network (semi-IPN) hydrogels were designed and prepared via a simple free radical polymerization reaction process initiated by a PVA-(NH4)2Ce(NO3)6 redox system. The structure of the PAM-g-PVA/PVP semi-IPNs was characterized by a Fourier transform infrared spectroscopy. The morphologies of PAM-g-PVA/PVP hydrogels and PAM-g-PVA/PVP/Ag nanocomposite hydrogels were examined by scanning electron microscopy and transmission electron microscopy (TEM). The experimental results indicated that the PAM, PVA or PVP chains can efficiently act as stabilizing agents for Ag nanoparticles. TEM investigation of sample morphology showed the presence of nearly spherical-, square- or rectangular-shaped Ag nanoparticles with diameters ranging from 10 to 60 nm. The characteristic surface plasmon resonance band appeared at 390–400 nm as a result of the immobilization of Ag nanoparticles within the hydrogel matrices. The self-assembly of Ag nanoparticles and the swelling behavior of the resulting nanocomposites can be controlled and modulated by altering the mole fraction of PVP in the PAM-g-PVA/PVP semi-IPNs.

ANATOLY FILIPPOV, MANJU AGARWAL, SERGEY VASIN, SUNIL DATTA — 2013 г.

Using cell model initiated by Happel, the filtration problem across a membrane composed of an aggregate of parallel circular cylinders subject to a uniform transverse magnetic field is studied. The system is simulated by a single cylinder enveloped by a concentric cylindrical enveloping surface with axial flow. The analysis leads to the evaluation of the permeability parameter. The results are then graphically presented and discussed. The effect of magnetic field is seen to increase the permeability.

БАКЕЕВ Н.Ф., ВОЛКОВ А.В., ВОЛЫНСКИЙ А.Л., ДЕМЕНТЬЕВ А.И., ЗЕЗИН С.Б., МОСКВИНА М.А., ПОЛЯНСКАЯ В.В., ТУНЯН А.А. — 2013 г.

Разработан метод получения (с использованием явления крейзинга) гибридных пленочных механически прочных полипропиленовых композиций с нанофазой аморфной двуокиси титана (до 30 мас. %). Морфология композиции в целом представляет собой взаимопроникающую сетку, в которой неорганический компонент (TiO2) распределен в нанопористой структуре полипропиленовой матрицы. Структура и состав аморфной двуокиси титана выглядят как ансамбль наночастиц TiO2 размером 1 нм (20 мас. %) в рыхлой сетке оксополимеров титана (80 мас. %), содержащей 30 мас. % боковых OC3H7- и ОН-групп, связанных с атомами титана.

HONGXIU SUN, JUNJI LIU, LEI ZHANG — 2013 г.

The diffusion-controlled adsorption kinetics of micellar surfactant C12E7 (heptaethylene glycol monododecyl ether) solutions was studied theoretically and experimentally. The corrected diffusion equation, which was used to describe the diffusion of the monomers in the micellar solutions, was solved under the initial and boundary conditions by means of Laplace transformation. The dynamic surface adsorption t) as a function of surface lifetime t, monomer diffusion coefficient D and the demicellization constant was derived. The dynamic surface tensions (t) of aqueous submicellar and micellar solutions were measured via maximal bubble pressure method. By analyzing the experimental data, the determined demicellization constant of C12E7 at 25°C was between 100 116 s-1.

JIRI SKVARLA, SANDOR BARANY — 2013 г.

The effect of cationic and anionic surfactants, as well as cationic and anionic polyelectrolytes (PE), their binary mixtures on the electrokinetic potential of monodisperse carboxylated polystyrene (PS) particles as a function of the reagents dose, pH, the charge density (CD) of polymers, the surfactant/PE and binary PE mixture composition, and sequence of components addition to the suspension has been studied. It has been shown that addition of increasing amount of anionic surfactant/polyelectrolytes increases the absolute value of the negative zeta-potential of PS particles; this increase is stronger the CD of the PE and pH of the system are higher. Adsorption of cationic surfactant/polyelectrolytes leads to a significant decrease in the negative -potential and to overcharging the particles; changes in the -potential are more pronounced for PE samples with higher CD and for suspensions with lower pH values. In mixtures of cationic and anionic PE, in a wide range of mixture composition, the -potential of particles is determined by the adsorbed amount of the anionic polymer independently of the CD of PEs and the sequence of addition of the mixture components. The isoelectric point of the surface is reached at the adsorbed amount of positive charges of PE that is approximately equal to the surface CD of particles. The laws observed were explained by features of macromolecules conformation in adsorbed mixed PE layers. Considerations about the role of coulombic and non-coulombic forces in the mechanism of anionic/cationic PE adsorption are presented.

JIRI SKVARLA, SANDOR BARANY — 2013 г.

The effect pH, ionic strength (KCl concentration), weakly and medium charged anionic and cationic polyelectrolytes (PEs) as well as their binary mixtures on the electrokinetic potential of silica particles as a function of the polyelectrolyte/mixture dose, its composition, charge density (CD) of the PE, and way of adding the polymers to the suspension has been studied. It has been shown that addition of increasing amount of anionic PEs increases the absolute value of the negative zeta-potential of particles at pH > pH isoelectric point (IEP = 2.5); this increase is stronger the charge density of the polyelectrolyte is higher. Adsorption of cationic polyelectrolytes at these pH values gives a significant decrease in the negative -potential and overcharging the particles; changes in the -potential are more pronounced for PE samples with higher CD. In mixtures of cationic and anionic PE at pH > pHIEP, the -potential of particles is determined by the adsorbed amount of the anionic polymer independently of the CD of PEs, the mixture composition and the sequence of addition of the mixture components. Unexpectedly, the -potential of silica at pH = 2.1, i.e.

KHARATYAN E., MASALOVA I. — 2013 г.

Water-in-oil, high internal phase emulsion made of super-cooled aqueous solution containing a mixture of inorganic salts and stabilized with non-ionic surfactant (sorbitan monooleate) alone was investigated. It was not possible to produce a highly concentrated emulsion (with aqueous phase fraction = 94 wt %), stabilized with surface-treated silica, solely: we were able to form an emulsion with a maximal aqueous phase mass fraction of 85 wt % (emulsion inverts/breaks above this concentration). The inversion point is dependent on the silica particle concentration, presence of salt in the aqueous phase, and does not depend on the pH of the dispersed phase. All emulsions stabilized by the nanoparticles solely were unstable to shear. So, the rheological properties and stability of the emulsions containing super-cooled dispersed phase, with regards to crystallization, were determined for an emulsion stabilized by non-ionic surfactant only. The results were compared to the properties obtained for emulsions stabilized by surface treated (relatively hydrophobic) silica nanoparticles as a co-surfactant to sorbitan monooleate. The influence of the particle concentration, type of silica surface treatment, particle/surfactant ratio on emulsification and emulsion rheological properties was studied. The presence of the particles as a co-stabilizer increases the stability of all emulsions. Also, it was found that the particle/surfactant ratio is important since the most stable emulsions are those where particles dominate over the surfactant, when the surfactants role is to create bridging flocculation of the particles. The combination of the two types of hydrophobic silica particles as co-surfactants is: one that resides at the water/oil interface and provides a steric boundary and another that remains in the oil phase creating a 3D-network throughout the oil phase, which is even more beneficiary in terms of the emulsion stability.

KARAKASHEV STOYAN I., NGUYEN ANH V., ROUMEN TSEKOV — 2013 г.

The present work is trying to explain a discrepancy between experimental observations of the drainage of foam films from aqueous solutions of sodium dodecylsulfate and the theoretical DLVO-accomplished Reynolds model. It is shown that, due to overlap of the film adsorption layers, an adsorption component of the disjoining pressure is important for the present system. The pre-exponential factor of this adsorption component was obtained by fitting to the experimental drainage curves. It corresponds to a slight repulsion, which reduces not only the thinning velocity as observed experimentally but corrects also the film equilibrium thickness.

KHARATYAN E., MASALOVA I., TSHILUMBU N.N. — 2013 г.

The water-in-oil high internal phase emulsions were the subject of the study. The emulsions consisted of a super-cooled aqueous solution of inorganic salt as a dispersed phase and industrial grade oil as a continuous phase. The influence of the industrial grade oil type on a water-in-oil high internal phase emulsion stability was investigated. The stability of emulsions was considered in terms of the crystallization of the dispersed phase droplets (that are super-cooled aqueous salt solution) during ageing. The oils were divided into groups: one that highlighted the effect of oil/aqueous phase interfacial tension and another that investigated the effect of oil viscosity on the emulsion rheological properties and shelf-life. For a given set of experimental conditions the influence of oil viscosity for the emulsion stability as well as the oil/aqueous interfacial tension plays an important role. Within the frames of our experiment it was found that there are oil types characterized by optimal parameters: oil/aqueous phase interfacial tension being in the region of 19–24 mN/m and viscosity close to 3 mPa s; such oils produced the most stable high internal phase emulsions. It was assumed that the oil with optimal parameters kept the critical micelle concentration and surfactant diffusion rate at optimal levels allowing the formation of a strong emulsifier layer at the interface and at the same time creating enough emulsifier micelles in the inter-droplet layer to prevent the droplet crystallization.

ANATOLY FILIPPOV, ASHISH TIWARI, ELENA SHERYSHEVA, MANOJ KUMAR YADAV, PRAMOD KUMAR YADAV, SATYA DEO, SERGEY VASIN — 2013 г.

This paper concerns the hydrodynamic permeability of biporous medium built up by porous cylindrical particles located in another porous medium by using cell model technique. It is continuation of the previous work of authors where biporous membrane was built up by porous spherical particles embedded in accompanying porous medium. Four known boundary conditions, namely, Happels, Kuwabaras, Kvashnins and Cunningham/Mehta-Morses, are considered on the outer surface of the cell. The variation of hydrodynamic permeability of biporous medium (membrane) with viscosity ratio, Brinkman constants, and solid fraction are presented and discussed graphically. Comparison of the resulting hydrodynamic permeability is undertaken. Some previous results for dimensionless hydrodynamic permeability have been verified.

HONGLAN CAI, HUIHONG LU, XUEQIN AN — 2013 г.

The kinetics of the cycloaddition of nitrosobenzene with 2,3-dimethyl-1,3-butadiene in solutions of anionic sodium di(2-ethyl-1-hexyl) sulphosuccinate (AOT) and cationic cetyltrimethylammonium bromide was investigated. The significant acceleration of the reaction rate by a factor of 5 compared to that in a pure ethylene glycol was observed. Isobaric activation parameters were determined, and the activation energy Ea was shown to decrease upon increasing AOT concentration in solutions with low surfactant concentrations.

JIANZHONG LOU, JINCHENG WANG, SIHAO CHEN, XINGYU DONG — 2013 г.

With polylactic acid (PLA) as shell and capsaicin as core substances, microcapsules were prepared based on solvent evaporation method. The orthogonal test was used to analyze the effects of the process conditions such as polyvinyl alcohol and PLA concentrations, stirring rate, and oil/water ratio on the particle size of the microencapsulated capsaicin (MC) agents. The chemical composition, morphology and size distribution of the microcapsules prepared by the most satisfactory conditions were analyzed by Fourier transform infrared spectroscopy, laser light scattering, and scanning electron microscopy. The MC agents had a mean diameter of 3 5 . The thermal properties of the MC agents were measured by differential scanning calorimetry and thermogravimetric analysis. It was demonstrated that the thermal stability of the MC agents was changed or even improved by the encapsulated PLA over the surface, when compared with similar parameters of the uncovered capsaicin. The in vitro release profile suggested that the microcapsules could be a suitable material for controlled release of capsaicin.P

AFTAB ASLAM PARWAZ KHAN, AL-YOUBI ABDULRAHMAN O., ANISH KHAN, ASIRI ABDULLAH M., DILEEP KUMAR, MALIK ABDUL RUB, NAVED AZUM, RAHMAN MOHAMMED M. — 2013 г.

Herein we report on the study of the interactions between alkanediyl- -type cationic dimeric (gemini) surfactant and the nonionic Triton X-100 in aqueous medium. The critical micelle concentrations of binary mixtures were determined by fluorometric study. Using the regular solution theory for the analysis of the experimental data, the attractive nature of interactions and synergistic behavior of gemini surfactant and Triton X-100 mixture were demonstrated. The micelle aggregation number was measured using steady state fluorescence quenching method. The micropolarity, binding constant and dielectric constant of mixed systems were determined from the ratio of peaks intensity (I1/I3) in the pyrene fluorescence emission spectrum.

ANATOLY FILIPPOV, MANOJ KUMAR YADAV, PRAMOD KUMAR YADAV, SATYA DEO — 2013 г.

This paper concerns the slow viscous flow of an incompressible fluid past a swarm of identically oriented porous deformed spheroidal particles, using particle-in-cell method. The Brinkmans equation in the porous region and the Stokes equation for clear fluid region in their stream function formulations are used. Explicit expressions are investigated for both the inside and outside flow fields to the first order in a small parameter characterizing the deformation. The flow through the porous oblate spheroid is considered as the particular case of the porous deformed spheroid. The hydrodynamic drag force experienced by a porous oblate spheroid and permeability of a membrane built up by porous oblate spheroids having parallel axis are evaluated. The dependence of the hydrodynamic drag force and the hydrodynamic permeability on particle volume fraction, deformation parameter and viscosity of porous fluid are also discussed. Four known boundary conditions on the hypothetical surface are considered and compared: Happels, Kuwabaras, Kvashnins and Cunninghams (Mehta–Morses condition). Some previous results for hydrodynamic drag force and hydrodynamic permeability have been verified. The model suggested can be used for evaluation of changing hydrodynamic permeability of a membrane under applying unidirectional loading in pressure-driven processes (reverse osmosis, nano-, ultra- and microfiltration).

JIN-CHUL KIM, MI SUN LEE — 2013 г.

Photo-responsive microspheres were prepared by dispersing hydrophobically modified poly(vinyl alcohol)-epoxypropoxy coumarin conjugates (HmPVA-EPC) in an aqueous phase. These conjugates were prepared by subsequent covalent attachment of decanoyl chloride (DC) to PVA, and then EPC to HmPVA. The air/water interfacial activities of HmPVA-EPC were higher than unmodified PVA, due to the hydrophobicity of DC moiety. Under a cyclic irradiation by 365 and 254 nm light, the degree of photo-dimerization of EPC residues of HmPVA-EPC was as high as that of free EPC. The obtained HmPVA and HmPVA-EPC were immobilized into submicron-sized microspheres. The degree of Nile Red release from HmPVA-EPC microspheres was more than 75% within 24 h that was higher than the value of 40% for HmPVA microspheres. This difference is most likely due to the less compact packing of HmPVA-EPC in the microspheres due to the smaller number of hydrophobic DC residues. The dye release from HmPVA-EPC microspherses was inhibited by the irradiation with 365 nm light, possibly due to the photo-induced cross-linking of the polymer.

GUANGHONG HE, LIPING XU, WEIJUN LIU — 2013 г.

In this study, temperature-sensitive amphiphilic core-shell nanoparticles of N-isopropylacrylamide (NIPAM) were prepared via interfacial in situ polymerization of styrene (S) and NIPAM. Oil soluble cumene hydroperoxide (CHPO) oxidizer and water soluble reductant iron(II) sulfate (FS), polyurethane and hexadecane were used as interfacial initiation pair, surfactant and co-stabilizer, respectively. Radicals are produced and initiate polymerization only when the CHPO and FS are present at oil/water interface. FT-IR and 1H NMR spectroscopy confirmed the co-polymerization of these monomers. The core-shell structure with a diameter 150 nm was corroborated by TEM and FESEM. DSC analysis showed the existence of two glass transition temperatures of the resulting particles. Salt-tuned phase separation behavior of poly(S-co-NIPAM) core-shell particles has been studied by dynamic light scattering. The lower critical solution temperature of the core-shell particles decreased linearly as a function of NaCl concentration that was attributed to the “salt out effect”. The variation of particle diameter showed a sigmoidal plot as a function of temperature regardless of the salt concentration.

AMINUL ISLAM MD., MUHIBUR RAHMAN M. — 2013 г.

Soluble colloidal MnO2 was prepared by the reduction of KMnO4 by three reducing agents as MnSO4, Na2S2O3 and HCOOH in neutral aqueous solutions at 25°C. Under suitable conditions, these solutions were dark brown in color and found to remain stable and transparent for several weeks. The obtained colloid was characterized by spectrophotometric and coagulation methods. The spectral behavior of soluble colloidal MnO2 was studied. The max was 390 nm when MnO2 was prepared by the reduction of KMnO4 by MnSO4. Both the max and the molar extinction coefficient depended on the method of preparation of colloidal MnO2. The formation of MnO2 was confirmed by the determination of the oxidation state of Mn-species in MnO2. The behavior of as-prepared colloidal solution obeys Beer Lambert law, if the concentrations of the colloidal particles are assumed to be equal to [MnO ]0. Both spectral analysis and that using Rayleighs law confirmed the existence of colloidal MnO2. The observed coagulating efficiency depends not only on the concentration of electrolyte but also on the charge carried by the cation of the electrolyte. Stability of the colloidal particles in the aqueous solutions is determined by the negative charge on the surface of the colloidal particles.

ALI A., BEHERA K., BHUSHAN V., MALIK N.A. — 2013 г.

Thermodynamic properties of sodium dodecyl sulfate (SDS) in micellar aqueous solutions of L-serine and L-threonine were determined by fluorescence spectroscopy and dynamic light scattering techniques. The values of Gibbs free energy, enthalpy and entropy of the process of micelle formation were calculated using the critical micelle concentration and degree of dissociation. Changes in critical micelle concentration of SDS with the addition of amino acids were examined by both conductivity and pyrene I1/I3 ratio methods at different temperatures. The pyrene fluorescence spectra were used to study the change of micropolarity produced by the interaction of SDS with amino acids. The aggregation behavior of SDS was explained in terms of structural changes in mixed solutions. The data on dynamic light scattering suggest that size of SDS micelles was influenced by the presence of amino acids.