Structure Effect on Miscibility of Butanol and Dodecyltrimethylammonium Chloride in Adsorbed Film

Miscibility of components in the adsorbed film for the n-butanol (NBA)-dodecyltrimethylammonium chloride (DTAC) and tert-butyl alcohol (TBA)-DTAC mixtures were investigated by measuring surface tension of the aqueous solutions. The experimental results were analyzed thermodynamically. Diagrams of the excess Gibbs energy in the adsorbed film gH,E vs the composition in the adsorbed film XH2 were obtained from the phase diagrams of adsorption. The gH,E values of the NBA-DTAC system are more negative than those of the TBA-DTAC system. It is concluded that the molecular interaction between NBA and DTAC is stronger than that between TBA and DTAC. With respect to the mean molar area in the adsorbed film A vs XH2 curve at a fixed surface tension gamma, the criterion of ideal mixing is demonstrated to be a straight line connecting the pure values. The A vs XH2 curves are convex downward in both systems and the deviation from the straight line is attributed to the dependence of gH,E on gamma. Copyright 1998 Academic Press.