Lyophilic structural-mechanical barrier

Often one relates this type of stabilization to the so-called steric factor [48-51], the notion of which was introduced much later than Rehbinder s concept of lyophilic structural-mechanical barrier. Steric factor primarily reflects configurational elasticity of tails and loops of adsorbed macromolecules as well as osmotic effects. Steric factor represents only an entropic ( generally speaking, small) contribution to the elastic resistance of film, and by itself can not account for the strong stabilization. 

REHBINDER S LYOPHILIC STRUCTURAL-MECHANICAL BARRIER AS A FACTOR OF STRONG COLLOID STABILITY... 

There are a number of experimental methods that can be used to evaluate these two factors of a lyophilic structural-mechanical barrier separately. We will briefly review these methods in the succeeding text and then focus on specific experimental data that have been collected by employing these methods. 

In Rehbinder s concept of the stability of emulsions and other disperse systems, the focus is on the lyophilic structural-mechanical barrier as a factor responsible for the strong stabilization of disperse systems. This barrier is manifested with the interfacial surfactant adsorption layer formed predominantly with high molecular weight substances (the so-called protective colloids). This barrier on the one hand promotes the formation of a system with substantial mechanical strength that is capable of resisting coalescence and the rupture of the droplets and, on the other hand, is lyophilic with reference to the dispersion medium. The lyophilic nature of the barrier is characterized by a low value of the interfacial energy, o, on the side facing the dispersion medium. One can thus... 

Shchukin, E. D., Amelina, E. A., and V. N. Izmaylova. 2003. The lyophilic structure-mechanical barrier as a factor of dispersion strong stabilization. In Role of Interfaces in Environmental Protection, S. Barany (Ed.), pp. 81-90. Amsterdam, the Netherlands Kluwer Academic Publishers. 

The term structural-mechanical barrier was for the first time introduced by P. A. Rehbinder [2,46-48]. This is a strong factor of stabilization of colloidal systems related to the formation of interfacial adsorption layers of low and high molecular weight surfactants which lyophilize interfaces. The structure and mechanical properties of such adsorption layers are able to ensure very high stability of dispersion medium interlayers between dispersed particles. 

When present at high concentration, polymeric surfactant, due to its high adsorption, may form a dense lyophilizing adsorption layer at the particle surface. Under these conditions the same polymer acts as a stabilizer of colloid dispersion, stabilizing the latter by means of structural-mechanical barrier (Chapter VII). 

It is worth emphasizing here that while the structural-rheological properties (i.e., mechanical strength) of the interfacial adsorption layer play a determining role in the stability of the system toward coalescence, they alone may not be sufficient for complete stabilization. The prevention of coagulation also requires that the structural-mechanical barrier formed is lyophilic (hydrophilic) with respect to the surrounding polar liquid. The latter can be achieved by the introduction of common surfactants, for example, sodium dodecyl sulfate (SDS). 

Professor Shchukin also performed general editing of the manuscript utilizing his experience in lecturing this course and paying special attention to the presentation of the concepts and applications of physical-chemical mechanics of disperse systems and materials, properties of the structure-rheological barrier as a factor of strong stabilization, some features of lyophilic colloidal systems and other research areas, explored by Russian scientific schools and less known abroad. 

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