J. L. Del Castillo

Micellization of decyldimethylbenzylammonium chloride at various temperatures studied by densitometry and conductivity

Abstract The critical micelle concentration (cmc), ionization degree of micellization, β , and standard free energy of micellization, Δ G 0 m , of decylbenzyldimethylammonium chloride in aqueous solution at 15, 25, 35, 45 and 55°C have been estimated from conductivity data. A shallow minimum of the cmc value appears at around 35°C. The apparent molar volumes of the monomeric and micellized surfactant were estimated from density data measured at 15, 25 and 35°C. It is suggested that release of water molecules from the hydration shell of the counter-ions may be an important contribution to the observed apparent expansion of the surfactant upon micellization.

Micellar behavior of tetradecyldimethylbenzylammonium chloride in water-alcohol mixtures.

The effect of butanol and benzyl alcohol on the critical micelle concentration and the degree of ionization of micelles of tetradecyldimethylbenzylammonium chloride has been studied conductometrically in the temperature range of 5 to 40 degrees C at 5 degrees C intervals. The results indicate that some self-association process of benzyl alcohol in the aqueous phase commences when its concentration amounts to ca 0.05 m. By applying the theoretical treatment suggested by Motomura for binary surfactant systems, the molar fraction of alcohol in the micelle and the standard free energy of solubilization were estimated from the dependence of cmc on temperature and alcohol concentration. For comparative purposes the micellar properties of tetradecyltrimethylammonium bromide in water-alcohol systems at 25 degrees C have also been studied.

Apparent molar volumes of benzyltrimethylammonium bromide and its homologs in aqueous solution at 15, 25, and 35° C

Apparent molar volumes at infinite dilution of benzyltrimethylammonium bromide and its butyl and hexyl homologs at 15, 25, and 35°C and of dibenzyldimethylammonium bromide at 25°C in aqueous solution were estimated from density measurements. The additivity rule for the contribution of the methylene groups to the apparent molar volumes was found to be obeyed within a broad range of homologs, which covers the parent salt and the dodecyldimethylbenzylammonium bromide. The volumetric contribution of the phenylene (–C6H4–) group was estimated to be 61 cm3-mol−1 at 25°C. A value of −16.9 ± 0.3 cm3-mol−1 was suggested for the volumetric contribution of the N+ fragment to the apparent molar volume of alkylbenzyldimethylammonium salts.