Behavior of hexadecyltrimethylammonium bromide and Triton X-100 mixture in the bulk phase of aqueous solution in the presence of methanol and propanol

Measurements of density, dynamic viscosity and specific conductivity of the aqueous solutions of p-(1,1,3,3-tetramethylbutyl)phenoxypoly(ethylene glycol) (Triton X-100 or TX-100) and hexadecyltrimethylammonium bromide (CTAB) with methanol or propanol were made. The surfactant mixture concentration ranged from 1 × 10− 6 to 3 × 10− 2 M and the mole fraction of alcohol changed from 0 to 1. From the obtained results the critical aggregation concentration (CAC) of alcohol and the critical micelle concentration (CMC) of surfactant mixture were determined. It proved that the short-chain alcohols considerably affect the CMC of surfactants, but surfactants only slightly affect the CAC of alcohols. Moreover, surfactants form micelles only in the range of alcohol concentration below its CAC. Methanol can be treated only as a cosolvent while propanol depending on its concentration range acts as both a cosurfactant and cosolvent. The apparent and partial molar volumes of alcohol, water and surfactant mixture were determined from the commonly known equations. It appeared that these volumes can be also predicted on the basis of the bond lengths and angles between atoms in the molecules as well as the average distance between molecules by approximating the volume of certain functional groups by cages. The composition of mixed TX-100 + CTAB micelles was determined from the Rosen's theory of regular solutions. The standard Gibbs free energy of micellization and aggregation was also evaluated. The specific conductivity changes for the studied solutions with methanol or propanol were compared.