Some Colloid-Chemical Aspects of the Small Particles Contact Interactions

Abstract

Depending on the character of the particles’ interaction, two main types of the particle contacts (and, respectively, two types of disperse structures) can be considered, namely, coagulational and phase contacts [1–3]. In coagulational contacts, disperse phase particle adhesion is limited to simple “touching”, either directly or by means of a residual layer of dispersion msdium, mainly due to molecular van der Waals forces. These contacts are not strong (e.g., 10^-9 – 10^-7 N) and are mechanically reversible, predetermining the viscoelastic properties of the corresponding thixotropic systems. A phase contact, on the other hand, is the result of bridging of particles (by displacing the dispersion medium from an area much bigger than the sizes of elementary cell) due to the same valence bonding as in the bulk of the given phase. These contacts are relatively strong (e.g., 10^-6 N and higher) and, generally speaking, are mechanically irreversible. Elastic-brittle or elastic-plastic behavior is typical for these structures. Phase contacts determine the material’s quality during use. In contrast, properties of coagulational contacts (and corresponding systems) are important during numerous steps of the material production and forming, especially when easy mobility is required. In diluted systems (sols), interactions of particles (energy of adhesion in contact being compared with the kT value) predetermines aggregative stability of a system.