Equilibrium studies of soluble films of short-chain monocarboxylic fatty acids at the organoliquid-vapour phase boundary
The behaviour of acetic, propionic and butyric acids in solutions of benzene, carbon tetrachloride and cyclohexane at the solution-vapour phase boundary has been investigated at 30°. Surface tensions and vapour pressures of the solutions are determined, and the Gibbs adsorption equation used to calculate surface excesses Γ(N)2. The amounts of the individual components at the interface are computed by well-known methods. The results are consistent with a monolayer model of adsorbed phase with the acid molecules assuming a parallel orientation. Adsorption of acid increases with chain length for benzene and carbon tetrachloride solutions but is the reverse for cyclohexane solutions. The occurrence of a mixed monolayer is observed for all the systems, and a monolayer of acid alone is formed only from pure acid.