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

The structure-mechanical barrier as the factor of dispersions stability was introduced by academician Rehbinder. Peculiarities of the display of struc ture mechanical barrier in stability of foams and emulsions and, respective ly, thin liquid films, when protein interfacial layers with specific rheolo gical behaviour (especially, elasticity) are formed at surfaces, are consid ered 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 q uasi-two-dimensional solid-like structures, correlating, in these condition s, with infinite rise in dispersion stability. The quantitative judgement o n structure mechanical barrier was obtained as the evaluation of the energi es (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 failur e of protein adsorption layers in coalescence processes is analyzed. Kineti c parameters of drops coalescence in emulsions and individual drops at the flat interface of a macroscopic liquid phase allow to distinguish the syste ms stable due to Rehbinder's structure mechanical barrier from unstable dis persions. 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 uni versal character of structure mechanical barrier. (C) 1999 Elsevier Science B.V. All rights reserved.