Binary phase equilibria of three α-methyl-substituted sodium alkanoate surfactants

Abstract

In this work, we continue our study of methyl-substituted surfactants and present the aqueous binary phase diagrams of racemic sodium 2-methyloctanoate, -nonanoate, and -dodecanoate, respectively. All systems have very low Krafft temperatures within the solution phase, between 1 and 4 °C. The phase sequences of the two shorter surfactants are very similar to those of the unsubstituted sodium octanoate, although with somewhat different range of existence for the phases formed. The sodium 2-methyldodecanoate system is different from the unsubstituted sodium dodecanoate system, as the former seems to lack a hexagonal phase. The surfactant systems were delineated using 2H NMR splittings and crossed polarizers, and combined with SAXS for determination of phase structure.