A. E. Kharlov

Non-Newtonian behavior of concentrated emulsions stabilized with globular protein in the presence of nonionic surfactant

Changes in the rheological properties of a model concentrated oil-in-water emulsion stabilized with globular protein (bovine serum albumin) upon the addition of nonionic surfactant polyoxyethylene (20) sorbitan monooleate (Tween 80) are studied. Non-Newtonian behavior is typical of the emulsions in question; moreover, they are characterized by the existence of yield stress. At stresses above the yield stress, the viscosity drops not immediately but after the intermediate Newtonian region at the flow curve. For all systems studied, the total flow curve is exhibited with the minimum Newtonian viscosity that is adequately described by the Cross formula. An increase in the Tween 80 concentration leads to a decrease in the viscosity of emulsion. Two threshold phenomena on the concentration dependences of rheological properties are revealed: at low concentration of added nonionic surfactant, the yield stress drops abruptly, whereas the viscosity lowers considerably with an increase in surfactant concentration to 1 × 10−3 mol/l and the emulsion becomes unstable. The effects observed can be explained by the gradual displacement of high-molecular-weight stabilizer from interfacial layers and its replacement by nonionic surfactant.

Peculiarities of the surface crystallization of sodium chloride on mucin films

It is established that the two-dimensional crystallization of sodium chloride on the surface of a biopolymer film (film of a glycoprotein, mucin), which is used as a template, gives rise to the formation of crystals with unusual morphology—in particular, dendrites. This type of crystallization is observed in two cases—namely, when drying a film formed from a salt-containing mucin dispersion and when drying a salt solution droplet on the surface of a dry mucin film obtained from a salt-free mucin dispersion. Mechanisms leading to unusual salt crystallization are discussed, and the role of specific interactions of sodium chloride with mucin is shown.

Viscoelasticity of concentrated emulsions stabilized by bovine serum albumin in the presence of a nonionic surfactant

Viscoelastic properties of highly concentrated toluene-in-water emulsions stabilized by mixtures of bovine serum albumin and a nonionic surfactant, polyoxyethylene(20)sorbitan monooleate, are studied by a dynamic method in a wide frequency range. It is shown that an increase in the relative content of the surfactant results in a suppression of the system elasticity and a decrease in the relaxation time. A direct correlation is found between the dynamic and steady rheological characteristics of the systems under examination. The latter fact confirms indirectly that the viscoelasticity of the emulsions is due to the presence of the high-molecular-mass component in interfacial layers.

Black foam films stabilized with the mixtures of bovine serum albumin and nonionic surfactant tween 80

Stable black films are prepared for the first time from aqueous solutions of Tween 80-bovine serum albumin mixtures. Conditions for their formation and stabilization factors are studied in a Scheludko-Exerowa cell by microinterferometry. It is found that such films are formed when saturated surface layers consist of surfactant-protein 1: 1 complexes, Tween 80 molecules, or their mixtures. A possible mechanism for the thinning of liquid layers and the stabilization of black films is discussed.

Mixed monolayers of bovine serum albumin with a nonionic surfactant (Tween 80)

Mixed monolayers of bovine serum albumin (BSA) with a nonionic surfactant (Tween 80) are obtained by spreading solutions containing both components over the surface of a subphase (water with pH 6) over a wide range of solution compositions. According to compression-expansion isotherms, the mixed monolayers are of the condensed type when the BSA concentrations in the solution are far higher than or equal to the surfactant concentration. Such monolayers mostly consist of BSA-Tween 80 (1: 1) complexes. In contrast, a BSA monolayer is of the expanded type. When Tween 80 in the solution prevails over Tween 80, the monolayers become unstable. The results of this work pertain to the monitoring of the properties of protein-surfactant mixtures and design of Langmuir-Blodgett (LB) films.

Monolayer Parameters of Gelatin Chemically Modified with N-Hydroxysuccinimide Ester of Caprylic Acid

The behavior of gelatin chemically modified with N-hydroxysuccinimide ester of caprylic acid at the aqueous (NH4)2SO4 solution–air interface is studied. The compression isotherms of gelatin monolayers whose pattern is dependent on the degree of gelatin modification are obtained. It is established that the area corresponding to the beginning of isotherm rise, two-dimensional pressure of completely compressed monolayer, and the modulus of monolayer surface elasticity increase with the degree of gelatin hydrophobization. The surface (“adsorption”) activity of gelatin with the modification degree of 85% is approximately threefold higher than for the initial gelatin.

Preparation of miniemulsions of plant extracts

The composition and technology for the preparation of a combined water solution of hydrophobic plant extracts, eucalymine and estifan are developed. The concentration of surfactants (Tween 20 and 80) and soya lecithin that is optimal for obtaining stable miniemulsion systems is determined. The sizes and zeta potential of the obtained dispersed nanoscale particles are established.

Adsorption modification of solid surfaces with aqueous solutions of fullerene C 60 derivatives containing maleimide and dipeptide addends

The regularities of the adsorption modification of different solid surfaces with aqueous solutions of amino-acid derivatives of fullerene C60 (ADF) that contain the maleimide and dipeptide addends were studied by the methods of wetting and Quartz Crystal Microbalance (QCM). It was found that, despite the absence of surface activity at the solution-air interface, ADFs are well adsorbed at the solution-solid interface. On high-energy surfaces with different charges in aqueous media, at neutral pH, the studied ADF act as ionic surfactants with polar groups charged opposite to the solid surface. The modification of polymers with AFD solutions results in the hydrophilization of their surfaces as in the case of classical low-molecular surfactants.

Imidazoline derivatives as promising cationic emulsifiers for styrene heterophase polymerization

The colloidochemical properties of new cationic surfactants synthesized from fatty acids of palm oil and diethylenetriamine are first studied. It is found that, at solution pH below 6.0, the examined surfactants exist mainly as salts formed from protonated surfactant molecules and residues of strong acids, e.g., hydrochloric acid. In the pH range above 7.0, the protonated and nonprotonated forms of the surfactants are at equilibrium, which shifts to the nonprotonated form with an increase in pH. The analysis of interfacial tension isotherms shows that the minimum values of the interfacial tension are achieved at pH 7.0 when the concentrations of the protonated and nonprotonated forms of surfactant molecules are equal. New cationic surfactants are used as emulsifiers in emulsion polymerization of styrene. It is found that stable polystyrene latexes with narrow particle size distributions and high positive ζ potentials (as high as +68.4 mV) can be obtained at styrene concentration in an initial emulsion of 25 vol % and surfactant concentration in an aqueous phase of 2 wt %. A hydrogen peroxide-iron(II) salt redox system is used as an initiator of polymerization at component concentrations equal to 5 and 0.05 wt % of the monomer, respectively.

Influence of the Molecular‐Mass Distribution of Gelatins Modified with a LIKI‐1 Tanning Agent on the Rheological Parameters of Interphase Adsorption Layers at the Interfase of an Aqueous Solution of Gelatin–Metaxylene

The influence of the interaction of gelatin with a protected formaldehyde tanning agent on the rheological parameters of interphase adsorption layers formed at the interface of a 0.1% aqueous solution of gelatin–metaxylene has been investigated as a function of the mass‐molecular distribution of initial gelatins. It has been shown that the chemical modification of gelatin with tanning agents weakens the process of gel formation in the interphase layer directly with the depth of the tanning process. This dependence is the most pronounced for gelatin with a high content of fractions with a molecular mass of more than 285 kDa.