Thermodynamic properties of aqueous micellar solutions of some new acetylated gluco-cationic surfactants

Abstract

Thermodynamic properties of the aqueous solutions of a newly synthesized homologous series of N-[2-(2,3,4,6-tetra- O-acetyl-β- d-glucopyranosyl)ethyl]- N, N-dimethyl- N-alkylammonium bromides with hydrophobic tails of 8, 12 and 16 carbon atoms, determined as a function of concentration by means of direct methods, are here reported for the first time. Dilution enthalpies, densities and sound velocities were measured at 298 K, allowing for the determination of apparent and partial molar enthalpies, volumes and compressibilities. Changes in thermodynamic quantities upon micellization were derived using a pseudo-phase transition approach. The trends of apparent and partial molar enthalpies versus m confirm the increase in global hydrophobicity of the molecule, already suggested by the value of the cmc of C 12AGCB, lower than that of DTAB, and show that, also in the case of surfactants with a bulky substitution on the polar head, the group contribution of the –CH 2– is additive both in the plateau (−1.3 kJ mol −1 group −1) and in the micellization enthalpy changes (−1.5 kJ mol −1 group −1). The determination of apparent molar volumes and compressibilities presents some experimental problems, due to the strong tendency of this class of surfactants to adsorb on the glass surfaces. Even so, the group contribution of the methylene group results as being additive and comparable to that of other cationic and anionic surfactants. From the comparison with DTAB, the volume of (2,3,4,6-tetra- O-acetyl-β- d-glucopyranosyl)ethyl group results as 291 cm 3 mol −1.