Surface and interfacial properties of octanoic acid-octylamine mixtures inisooctane-water systems: Influence of acid : amine molar ratio and aqueousphase pH

Surface tensions (ST), distribution ratios, and interfacial tensions (IFT) for octanoic acid-octylamine mixtures, dissolved either in water or in isoo ctane-water systems, have been investigated. Distribution ratios were obtai ned by determining the concentration of octanoic acid and octylamine using FTIR spectroscopy and latent variable regression. The dependence of the mea sured parameters on the molar ratio between octanoic acid and octylamine, a nd on the aqueous phase pH, was also studied. The results showed that the s imultaneous presence of protonated octylamine and dissociated octanoic acid had a significant effect on ST as compared to when either of the component s was present alone. The effect was largest for solutions of equimolar comp osition. IFT was significantly lower in systems containing the octanoic aci d:octylamine mixture as compared to systems containing only one of the comp onents. The dependence of IFT on pH was only significant for the mixed syst ems. In these systems a minimum in IFT was found around pH 7, and the varia tion in IFT with pH corresponded roughly to changes in the distribution rat ios with pH. (C) 2001 Academic Press.