Nonionic surfactant systems above the PIT Part I. Phase behaviour

Abstract

Just above the PIT for long nonionic amphiphiles C_mEO_n, the surfactant phase region (microemulsion area) and the water-poor domain tend to constitute a single oneisotropic phase region. According to the chemical nature of the oil (the third component), this phase domain coalescence takes place either directly toward the oil corner or for much larger surfactant/oil ratios, and give rise to typical phase diagram outlooks. Therefore, for intermediate water/surfactant ratio, a gap of solubility exists respectively for low or large oil contents, i. e. the molecular structures can be stable only in dilute or in concentrated solutions. The results are discussed in terms of the length/bulkiness and free volume of the oil molecules. We have also noted the absence of direct correlation between water solubilization and binary apolar phase behaviour.