Evidence for secondary minimum coagulation in a silica hydrosol obtained by dynamic light scattering

The coagulation kinetics of four different samples of a silica hydrosol differing in particle diameters (45, 101, 180, and 515 nm) were examined with the aid of photon correlation spectroscopy. The rate constants for rapid and slow coagulation were determined in the presence of LiCl and CsCl. The data analysis followed a method given by Versmold and Härtl. The stability ratio for a definite particle size at various electrolyte concentrations could be derived from the rate constants. The smallest particles were shown to be the most stable. This points to a coagulation in the secondary potential energy minimum, which could be proved by calculations of the stability ratio.