V. N. Izmailova

Development of the Rehbinder’s concept on structure-mechanical barrier in stability of dispersions stabilized with proteins

Abstract The structure-mechanical barrier as the factor of dispersions stability was introduced by academician Rehbinder. Peculiarities of the display of structure mechanical barrier in stability of foams and emulsions and, respectively, thin liquid films, when protein interfacial layers with specific rheological behaviour (especially, elasticity) are formed at surfaces, are considered to deeper insight the Rehbinder’s concept. Proteins are surface active substances with surface activity determined by details of their molecular structure. Adsorption of proteins at interfaces leads to the formation of quasi-two-dimensional solid-like structures, correlating, in these conditions, with infinite rise in dispersion stability. The quantitative judgement on structure mechanical barrier was obtained as the evaluation of the energies (forces) balance of molecular attraction and repulsion of elastic origin. Lifetime of dispersions is determined as the rupture probability of thin liquid films and stabilizing interfacial layers. The contribution of failure of protein adsorption layers in coalescence processes is analyzed. Kinetic parameters of drops coalescence in emulsions and individual drops at the flat interface of a macroscopic liquid phase allow to distinguish the systems stable due to Rehbinder’s structure mechanical barrier from unstable dispersions. Experimental results for fluid interfaces together with published data on repulsion between solid surfaces coated with protein on distances of twice the thickness of the protein adsorption layer, corroborate the universal character of structure mechanical barrier.

Properties of emulsion films made from binary aqueous mixtures of gelatin–surfactant: the effect of concentration and pH

Abstract The surface properties of the aqueous systems of gelatin and surfactants (anion and cation-active) with different component concentrations and pH at the organic interfaces were studied. The thermodynamic (interface tension) and rheological (yield shearing stress, viscosity) parameters of the bilateral emulsion films and interfacial adsorption layers stabilized by the gelatin–surfactant complexes organized in the volume were determined. The range of formation of the stable emulsion films was found. It was shown that the thermodynamic and rheological properties of the films and layers are extreme when gelatin macromolecules form complexes with the surfactant. These complexes make the interface structure thinner and have stronger then structures formed with free gelatin.

NMR method in the study of the interfacial adsorption layer of gelatin

Abstract The interfacial adsorption layers of gelatin at a benzene/gelatin solution in D 2 O interface were studied by NMR using the oil-in-water emulsions prepared by ultrasonic dispersion in conditions where the gelatin macromolecules are in a coiled conformation. The intensities of the proton signals from the gelatin decreased and the NMR spectral lines broadened upon the formation of interfacial adsorption layers of gelatin ( T > 3.13 K). The result is similar to that of collagen-like helices and gels of gelatin and shows that the fraction of mobile gelatin segments in interfacial adsorption layers decreases virtually to zero. The presence of two different signals in the NMR spectrum suggests that benzene is solubilized by gelatin macromolecules and constitutes one component of the interfacial adsorption layer of gelatin.

Rheological parameters of protein interfacial layers as a criterion of the transition from stable emulsions to microemulsions

Proteins are considered as surface active substances. On the basis of experimentally measured rheological parameters of interfacial layers, protein accumulation at an interface between two immiscible liquids, isotherms of interfacial tension, accounting theoretical ideas elaborated for multicomponent systems, the formation of interfacial layers was referred to phase transition. The property of proteins to stabilise emulsions supposedly is connected with the formation of middle phases of lamellar structure. The correlation between elastic properties of interfacial layers and a phase transition of the middle phase upon addition of salts or lipids has been shown. Lipids being added as cosurfactants lead to the transition from lamellar to other structures, which does not provide emulsion stabilisation.

Properties of Interfacial Layers in Multicomponent Systems Containing Gelatin

The review is devoted to the analysis of the effect of the addition of various surfactants on the composition, structure, and the properties of the interfacial adsorption layers (IALs) formed at equilibrium in the aqueous gelatin solution–hydrocarbon system. Associates of variable compositions that are determined by the component ratio and the concentration of added surfactant are formed due to the interaction between gelatin and surfactant. The formation of associates is equivalent to the modification of gelatin. The properties of the IALs of modified gelatins are discussed on the basis of our own results and published data on the interfacial tension, the mass accumulation of surface-active components at the interfaces during the IAL formation, the IAL rheological properties and the stability of emulsion films varied with the conditions of IAL formation (the nature of low-molecular-weight surfactant, component concentrations, pH of aqueous phase, and temperature). It was concluded that modified gelatins can be considered as new surfactants governing the dynamics of the formation and fracture mechanism of the IALs and the stability of emulsion films. The properties of the IALs of modified gelatins are compared with those of IALs formed by gelatin and low-molecular-weight surfactants under the conditions when associates are formed directly at the interface due to the use of oil-soluble surfactants.

Solubilization of oleophilic compounds in gelatin solutions containing surfactant

Abstract Solubilization of benzene (C6H6) and Sudan ‘Yellow’ (SY) in solutions of gelatin modified with ionic surfactants sodium dodecylsulfate (SDS) or cetylpyridinium chloride (CPC) has been investigated by refractometry and photocolorimetry. Biopolymer gelatin modified with low-molecular-mass surfactant can be regarded as a new surfactant whose properties are defined by the degree of its binding with gelatin. The mixtures of gelatin with SDS or CPC in a specific range of component ratios were found to exhibit synergism in solubilization of oleophilic compounds in the temperature range 295–318 K. The solubilizing capacity and volume of hydrophobic areas in the gelatin–surfactant complex were shown to attain their largest values at the isoelectric point. The thermodynamic parameters of solubilization (ΔG, ΔH, ΔS) were determined. The process is accompanied by a slightly negative change in the Gibbs energy and favored largely by an increase in entropy.

Properties of Spreaded Collagen I Monolayers on the Surface of Aqueous tert-Butanol and n-Hexanol Solutions

Properties of the monolayers of collagen isolated from the sclera of pigs eye are studied at the air–water interface with increasing tert-butanol or n-hexanol concentrations in a subphase. In the case of aqueous n-hexanol solutions, its adsorption on the subphase surface results in the formation of mixed monolayer whose properties depend on n-hexanol concentration in the subphase and the ratio between the number of alcohol and collagen molecules in the monolayer. At higher n-hexanol surface concentration, the phase separation of the monolayer into the domains of the condensed phase of alcohol and fibrous collagen occurs. A decrease in water activity in the presence of tert-butanol leads to a drastic reduction of collagen surface activity. This effect can be explained by both the constrained collagen spreading on the surface of tert-BuOH solutions and adsorption of alcohol molecules on collagen resulting in macromolecule hydrophilization. Alcohol critical concentrations are disclosed above which collagen monolayers are not formed.

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.

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.

Structure and Rheology of Foam and Emulsion Films of Gelatin-Surfactant

The natural polypeptide gelatin has the clearly defined surface activity, emulsifying, stabilizing properties and film-forming ability. To change its properties the gelatin macromolecules can be modified by the low-molecular-mass surfactants.