Gelation of Montmorillonite

THE combination of optical and elastic studies on sols of Wyoming bentonite containing the smallest particle sizes (15–20 mµ equivalent spherical diameter) have led to the conclusion that the gelation of this system is due to the formation of a fibrillar network in which the plates are aggregated end-to-end in the form of flat, ribbon-like filaments. The growth of these aggregates is indicated in Fig. 1, which shows the increase in the dissymmetry coefficient of the scattered light, and hence an increase in the size of the scattering unit, with increasing particle concentration. The values of the dissymmetry coefficient at infinite dilution correspond to rectangular plates of mean semi-perimeter 300 mµ, while the limiting values of the coefficient at the higher concentrations correspond to long flat filaments of mean width 100 mµ. On account of the irregularity in the particle size and shape, and the probability of incomplete aggregation, these estimates agree as well as can be expected with the mean values of 338 mµ and 150 mµ obtained from electron micrographs of the particles in our sols. The filamentary nature of these aggregates is confirmed by the angular intensity distribution of the scattered light, which fits closely to the theoretical curve.