Effects of hydrophobic chain length on temperature dependence of monolayer behavior of Ester-type tartaric geminis

Abstract

Ester-type tartaric gemini amphiphiles bearing two carboxyl groups and two hydrophobic alkanoyl groups were prepared from L-tartaric acid, and the pressure-area (π-A) isotherms for a series of symmetric tartaric gemini amphiphiles were measured by the conventional film-balance technique. The effects of the length of the hydrophobic alkanoyl chains and of the subphase temperature (Tsub) on the π-A isotherms for these compounds were examined. As the length of the hydrophobic alkyl chain increased, a more tightly packed monolayer was formed at the air-water interface. The melting temperature (Tm) of the monolayer on the water surface was evaluated from the subphase temperature (Tsub) dependence of the monolayer static elasticity εs, based on a π-A isotherm. A clear relationship between Tm and hydrophobic carbon number (n) was observed for 2D monolayers of tartaric geminis on water surfaces, as well as for fatty acids and/or 3D solids. Copyright ©2011 by Japan Oil Chemists' Society.