Self-association of an α,ω-type (bolaform) surfactant: Phase diagram, self—diffusion, and NMR studies of eicosane-1,20-bis(triethylammonium bromide)

Abstract

The binary phase diagram (temperature vs composition) of the cationic bolaform (α,ω-type) surfactant eicosane-1,20-bis (triethylammonium bromide) has been determined by polarizing microscopy and water deuteron NMR methods. The surfactant is easily soluble in water giving an extended isotropic solution phase followed by a normal hexagonal liquid crystalline phase (E) at higher surfactant concentrations. On increasing the temperature the liquid crystalline phase extends to the surfactant-rich side. The 2H NMR quadrupolar splitting values in the E phase are found to increase at first with increasing surfactant concentration, then to decrease and go through zero splitting; then the splitting values increase again sharply with increasing surfactant concentration. The micellar phase has a very low capacity to solubilize hydrophobic substances. The narrow 1H and 14N NMR bandwidths as well as the NMR self-diffusion data for water and surfactant indicate the formation of small, closely spherical miceless in the entire isotropic micellar solution phase.