Micelle formation of a cationic surfactant in the presence of 1,n-alkanediol and the miscibility of alcohols in micelles

Micelle formation of dodecyltrimethylammonium bromide (DTAB) was examined in the presence of α,ω-alkanediols applying conductivity measurements. Octanediol and hexanediol promoted the formation of mixed micelles of DTAB and the alcohol, but butanediol interfered with micellization. Analysis of the critical micelle concentration (cmc) based on the lattice model for mixed solution with the Bragg–Williams approximation indicated an unfavorable interaction between alcohol and water and a favorable interaction between the alcohol and surfactant, with the exception of butanediol. The exchange energy between alcohol and water was 0.5kT higher for alkanediol (C2n(OH)2) than for the corresponding regular alcohol (CnOH), which is believed to have resulted from the smaller mixing entropy for the alkanediol than for the corresponding regular alcohol. It was inferred from the analysis that the cmc increase for C4(OH)2 was caused by favorable interaction with water but unfavorable interaction with the micellar surfactant.