Variation of contact angle and structure with molecular length and surface density in adsorbed films of fatty acids

Abstract

Films of fatty acids from 12 to 22 carbons were prepared by adsorption on glass microscope slides from cetane solutions. Variations in density were achieved (1) by using a range of concentrations with a fixed short time of immersion and (2) by subsequent immersion in cetane of the most dense films.Electron diffraction patterns showed an increasing average tilt of the molecules relative to the surface normal with decreasing length of the molecules but no apparent change in tilt with variations in surface density. The contact angles exhibited by drops of cetane on the films decreased markedly from a maximum of 43-44[deg] when the density of the adsorbed molecules on the surface was decreased, but were independent of the variations in tilt and length of the molecules.