Pressure effects on micellar size

Abstract

Abstract The micellar radius of four cationic surfactant solutions, at high electrolyte concentration, has been determined as a function of increasing pressure and at several temperatures by quasi-elastic light-scattering techniques. The effective size of micelles may increase, decrease, or remain constant until the solubility limit is exceeded and phase separation occurs at high pressures. If the hydrodynamic radius is modified by pressure, the micelles will shrink at the lower temperatures, grow at the higher temperatures and shrink, then grow at intermediate temperatures. The pressure effect is most pronounced for cetyltrimethylammonium bromide and becomes progressively weaker as the alkyl chain is shortened from n = 16 to n = 14 and n = 12, as the electrolyte concentration is reduced and as the Br− counterion is replaced with Cl−.