Clustering of Liquid Molecules on Solid Surfaces

The strong self-association of DMSO, FA, DMFA, H2O controls their adsorption by swelling systems, for instance, by vermiculite, a mica-type layer silicate. Using this type of porous adsorbents the influence of the interlayer charges has to be reduced by replacing the interlayer cations by alkylammonium ions. In equilibrium with the liquids (DMSO, FA, DMFA, H2O, EtOH) the silicate layers are prized apart until distinct cavities for the sorption of the liquids are created. Their volumes are independent on the chain length of the alkylammonium ions.—The mutual influence between the clustered liquid molecules and the alkyl chain arrangements determines the interlayer structure. Therefore, substitution of alkylammonium ions by trimethyl alkylammonium ions not only changes the type of the liquid clusters but also the alkyl chain arrangement. Dimethyl dialkylammonium ions impede the formation of liquid clusters because of the strong van-der-Waals interactions between the chains, and only allow incorporating isolated guest molecules.—The surface excess isotherms describing competitive adsorption of DMSO and H2O show substantially linear sections. The DMSO/H2O ratio in the adsorbed phase is constant through most of the mole-fraction range of DMSO in solution (mole fractions DMSO from x1 = 0.15 to 0.95). DMSO is preferentially adsorbed, the ratio DMSO/H2O being 4–5.