SWELLING OF ALKYLAMMONIUM MONTMORILLONITES

Simultaneous vapor-phase adsorption isotherms and X-ray diffraction analysis of the c spacings for a series of n-alkylammonium bentonites supplied data from which a swelling mechanism is proposed. Adsorbates included methanol, ethanol, 1-propanol, water vapor, and n-heptane. The roles of the polar and nonpolar nature of the adsorbates were examined, and a two-step mechanism of swelling is suggested: first, adsorption of polar groups onto the silicate surface, and, second, displacement of the alkylammonium chain from the surface and solvation of the hydrocarbon chain by nonpolar species. The effect of adsorbing mixtures of polar and nonpolar adsorbates substantiates the proposed mechanism.