Amines as microemulsion cosurfactants

A systematic study of the phase behavior of short straight-chain amine amphiphiles in oil and water mixtures reveals large differences between amine and corresponding alcohol systems. The primary amine head group is more hydrophilic than alcohol, nitrile, carboxylic acid, ketone, and aldehyde head groups. The hydrophilicity of the amine head group is about the same as the hydrophilicity of the triethylene glycol head group, but butylamine is a more effective amphiphile on a mass basis than triethylene glycol monobutyl ether. Addition of acid strongly increases amine hydrophilicity while addition of base decreases amine hydrophilicity. In microemulsions, the effective hydrophilicity of the amine/anionic surfactant combination is lower than expected, indicating that a specific ionic interaction between amine and anionic surfactant is occurring in the surfactant-rich film separating oil and water domains.