Chemical relaxation and equilibrium studies of association in aqueous solutions of bolaform detergents. 2. Hexadecane-1,16-bis(trimethylammonium bromide) and dodecane-1,12-bis(tributylammonium bromide)

Abstract

The self association of dodecane-1,12-bis(tributylammonium bromide) and of hexadecane-1,16-bis(trimethylammonium bromide) (C 12Bu 6 and C 16Me 6, respectively) has been investigated by means of density, conductivity, emf, T-jump, and ultrasonic absorption. The results of conductivity and emf indicate no micelle formation in solutions of C 12Bu 6 up to concentrations of 5 × 10 −2 M. On the contrary conductivity, emf, and ultrasonic absorption studies reveal that C 16Me 6 forms micelles with an ionization degree close to 0.5 and a CMC of about 4.5 × 10 −2 M. These results are the first ones which clearly show micelle formation by bolaform detergents of the C m H 2 m+1 N(R) 3Br − type. The density data indicate that the volume change upon micellization is smaller than 1.5 cm 3/mole, which suggests a deep penetration of water into C 16Me 6 micelles. Some results, most notably the ultrasonic absorption ones, suggest a folding of the bolaform alkyl chain in the micellized as well as in the molecularly dispersed state. Nevertheless, the study of an alkane-α,ω-bis(trimethylammonium bromide) with an alkyl chain containing more than 16 carbon atoms appears necessary before a definite conclusion can be reached about the bolaform alkyl chain conformation.