Abstract
Conductivities, densities and ultrasonic speeds measurements of hexadecyltrimethylammonium bromide (HTAB) in aqueous solutions of glycine (Gly) and glycylglycine (Gly-Gly) have been made at various temperatures. The critical micelle concentration (CMC), the degree of ionization (beta) of the micelles, standard free energy, enthalpy, and entropy of the micellization process (Delta G (m) (A degrees) , Delta H (m) (A degrees) , and Delta S (m) (A degrees) ) for the present systems were estimated at different temperatures. The CMC values of HTAB in aqueous Gly and Gly-Gly were also evaluated by density and ultrasonic speed measurements. Apparent molar volumes, (V (I center dot)), apparent molar volumes at infinite dilution, (V (I center dot) (A degrees) ), apparent molar compressibilities, (K (I center dot)), of HTAB in the pre- and post-micellar regions, and volume change on micellization (Delta V (I center dot) (m) ) were also estimated. Large positive values of T Delta S (m) (A degrees) and small negative values of Delta H (m) (A degrees) suggest that micellization process is driven primarily by entropy increase. The increase in Delta V (I center dot) (m) and K (I center dot) with rise in temperature is indicative of less compact micellar structure of HTAB in presence of amino acid additives. These data suggest that amino acids are solubilised probably in the palisade layer of the micelle.