Adsorption of mixed cationic–non-ionic surfactants at the air/water interface

Abstract

Specular neutron reflection, in combination with hydrogen/deuterium isotopic substitution, has been used to investigate the adsorption of the mixed cationic–non-ionic surfactants hexadecyltrimethyl ammonium bromide, C₁₆TAB,–hexaethylene glycol monododecyl ether, C₁₂E₆, at the air/water interface. Measurements were made at surfactant concentrations from below to above the critical micellar concentration, c.m.c., of the mixtures. For the C₁₆TAB–C₁₂E₆ mixture, ideal mixing is observed at concentrations above the c.m.c. of the mixture whereas, below the c.m.c., departure from ideal mixing can be observed. The effects of temperature on the adsorption of the C₁₆TAB–C₁₂E₆ mixture at the air/water interface are described. The total adsorption decreases with increasing temperature and the surface becomes richer in the non-ionic component of the mixture.