Interlamellar Liquid Sorption on Hydrophobic Silicates

Abstract

AbstractA particular advantage of adsorption measurements on layer silicates is that the adsorption between the silicate layers can be followed by X‐ray measurements. — When the external and internal surface of the silicate montmorillonite is modified by increasing amounts of hexadecylpyridinium cations, the surface character changes from hydrophilicity to hydrophobicity. The changes are evaluated from the excess adsorption isotherms for methanol‐benzene mixtures. The volume Vs of the adsorption phase derived from the isotherms is compared with the free interlayer volume Vf from X‐ray measurements. — On sodium montmorillonite methanol is preferentially adsorbed and the volume increase observed by X‐ray measurements coincides with Vs. If the sodium cations are progressively displaced by hexadecylpyridinium ions the azeotropic point of the type IV isotherms is shifted to lower mole fractions of methanol. The methanol molecules are increasingly displaced from the adsorption phase by benzene molecules. Vf becomes strikingly larger than Vs. — It is concluded that the adsorption layer is not homogeneous in the interlayer space: the methanol molecules are adsorbed on the silicate layers and the benzene molecules are in the vicinity of the hexadecylpyridinium ions. In addition to this adsorption layer the remaining volume is filled with methanol‐benzene mixtures having a composition different from the adsorbed phase and more similar to the bulk phase.