Some new aspects of and conclusions on theory of stability of colloids and their experimental verification

Abstract

This paper considers three aspects of colloid stability theory: phase stability, the stability of disperse composition and aggregative stability in relation to the merits of a direct operational determination of the disjoining pressure. Four components of the disjoining pressure are treated: the dispersion, ion/electrostatic, adsorption and structural terms. The simplest and most general way to derive the second and third components of disjoining pressure is to use the Gibbs-Duhem equation generalized by inclusion of terms corresponding to the electric work of charging the particle interface. The theory of the adsorption component of disjoining pressure explains the stability of free films of some binary solutions demonstrated experimentally by Sheludko and Ekerova. With regard to other aspects of colloid stability we note that flow-ultramicroscopic measurements of the concentration of colloid particles are free from the shortcomings of other methods. This makes accessible the kinetics of slow coagulation of sols ( e.g., gold sols) and reveals the role of disaggregation here and in the establishment of aggregative quasi-equilibrium. The measurements of molecular attraction between crossed metal wires as a function of gap width are presented.