Selective adsorption of methyl esters on n-fatty acids at the silica/benzene and silica/carbon tetrachloride interface. Part 3.—Infrared studies and the structure of the solid surface

Abstract

A cell for studying the infrared absorption spectrum of species adsorbed at the solid/liquid interface is described. It has been used to study the spectra of a series of methyl esters of n-fatty acids at the silica/C₆H₆ and silica/CCl₄ interfaces. The results show that independent of whether the solid surface carries only isolated surface silanol groups or these and H-bonded silanol groups it is only the former species which act as adsorption centres. From each solvent the adsorbed molecules are held by H-bonding between the ester's carbonyl group and the surface silanol group. The absorption band of the perturbed surface silanol group is at 3450 cm^–1, suggesting that the H-bonding is of a localised form and does not include a contribution from solvent molecules.