The ionic dopant additives have different mechanisms of their influence upon MnO2 electrocrystallisation process and depending on dopants added the following polymorphs are stabilised: α-MnO2 (hollandite, I4/m) -NH + 4 ; γ-MnO2 (ramsdellite, P bnm) -Co 2+ , Fe 2+ ; layered polymorph δ-MnO2 (birnessite, C2/m) -Cr 3+ . The defect states of intergrowth method in ramsdellite matrix and twinning, OH groups studied by X-ray diffraction and the Fourier transform infrared mtehod, respectively, indicate their high content in case of Fe 2+ and Co 2+ -doped manganese dioxide. CVA oxygen reduction reaction peaks were established after experiments in alkaline electrolytes and dioxygen (argon, air) atmosphere. Activity of doped samples studied is comparable with other published data. Both doped with Co 2+ and Fe 2+ samples display maximal currents and some distinctive features in oxygen reduction reaction.
Pickering emulsion Nanoparticles Hydrophobic silica Emulsions Cream Emulsifiers are necessary components for preparation of important food and cosmetic emulsions. Among them prevalence was gained by solid emulsifiers, so-called Pickering's emulsifiers, and the phenomenon has received the name of Pickering's stabilization. The conditions of food and cosmetic emulsions' stabilization due to Pickering's effect on a number of model systems were studied checking possibilities of theoretical prediction of conditions of the most effective emulsions' stabilization. The model food and cosmetic emulsions with solid nanoparticles of silica, which received by heat treatment of the hydrophobic silicon dioxide at the different conditions have been considered. The subject of research was conditions of emulsions' stabilization by Pickering's nanoparticles. Searching for new emulsifier was made due to such reasons: emulsifier has to be cheap (as it gives essential contribution to the general cost value of finished goods at insignificant their concentration), available, harmless and, certainly, effectively stabilize emulsion's systems, reducing liquid-liquid interphase boundary energy. We have chosen the modified silicon dioxide which is inexpensive, available material, that is manufactured in Ukraine (Orisil M-200) and which was previously thermally processed for the purpose of decrease of hydrophobic groups' part on the surface and increase its stabilizing action. Degree of hydrophobicity of surface was determined by differential thermal and thermogravimetric analysis, and emulsifier was got from initial hydrophobic silica in the muffle furnace at certain temperature. Determination of the sizes of emulsifier's initial sample and after calcining was carried out by the dynamic light scattering method (Malvern Zetasizer Nano ZS). It was established that the optimum temperature and time, at which emulsifier with the best stability action is formed, are as follows: 600°C and 1 hour, respectively.
Keywords:Pickering Nanoparticles Silica Carbon Modeling Corresponding author:Oleksii Muratov E-mail: alzr@nuft.edu.ua DOI: 10.24263/2304-974X-2017-6-3-12 Introduction. The aim of this work is to predict and study the conditions for the stabilization of food and cosmetic emulsions with the Pickering effect establishing the possibility of mathematical modeling of conditions for the most effective stabilization of emulsions.Materials and methods. It was studied a model emulsions with injected solid nanoparticles based on water and triglycerides of carboxylic acids such as Glyceryl tributyrate (C4), Glyceryl tricaprylate (C6), and Glyceryl trioleate, linseed oil (a mixture of triglycerides of acids: 9-11% of palmitic and stearic, 13-29% of oleic, 15-30% of linoleic, 44-61% of linolenic acids) and their ethyl esters with a similar composition, and perfume oil. Calculations of surface tension and stability for the model systems of food and cosmetic emulsions were carried out by means of MathCAD-2000 software by Binks method.Results and discussion. It was calculated free energy values of a spherical nanoparticle (in k B T units, T = 298 K) which occupies position at the water / oil interface (tributyrin, tricaprylin, triolein, linseed oil and their ethyl esters, perfume oil). The stability of a particle is characterized by the energy barrier, from the side of one of the liquids. In connection with the fact that the energy wells are parabolas, it was collected information on the magnitude of the barriers and the position of the minimum when the particle is moved from the minimum with the z m coordinate into water (z = -1) and into oil (z = 1). The best energy well parameters of this solid emulsifier were about 2830 (in linseed oil and in their ethers), 4010 (perfume oil), 400 (triolein) and 150 k B T (tributyrin). It was shown that a nanoparticle consisting of 50% hydrophilic silica possesses the best stabilizing properties.Conclusions. The principal possibility of theoretical prediction of the conditions for the stabilization of food and cosmetic emulsions by the Pickering effect is shown. Stabilizing particles, which corresponds to optimal selection of the nanoparticle material, are consisting of 50% hydrophilic silica.
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