Ionization of monolayers of fatty acids from C 14 to C 18

Abstract

The force-area and potential-area characteristics of monolayers of the C 14-C 18 saturated fatty acids have been studied on 0.01 M NaCl substrates as a function of pH. The contraction observed for partly ionized films is explained in terms of an increased head-group attraction rather than an increased interaction between the paraffin chains resulting from a rearrangement of the molecules. The expansion occurring at high degrees of ionization is attributed to repulsion between the charged head groups. When the pH is greater than 10, minute traces of alkaline earth impurity exert a profound influence on the physical properties of stearic acid monolayers. These impurities can be effectively sequestered by the prior spreading and removal of several fatty acid monolayers.