The nature of lyophobic coating and the adsorption of organic molecules and water on modified silicas

The protective properties of lyophobic layers of various natures chemically grafted to a silica carrier were comparatively studied. The modifiers were silanes with the compositions CF3(CH2)(2)Si(CH3)(2)Cl (CF3), C8H17Si(CH3)(2)Cl (C8H17), and ClSi(CH3)(2)[OSi(CH3)(2)](2)Cl (OMS). The differences between the surface properties of chemically modified silicas observed in adsorption, chromatographic, and IR spectroscopic measurements were shown to be related to a nonuniform electron density distribution in CF3 grafted radicals and the special features of the structure of CF3 and OMS grafted layers caused by the possibility of interaction between the terminal groups of these radicals and the surface of the carrier. Modified silicas possessed low surface energy and were superhydrophobic materials. The sample with grafted octyl groups C8H17 had the highest stability with respect to water.