Chemical relaxation and equilibrium studies of association in aqueous solutions of bolaform detergents. 3. Docosane-1,22-bis(trimethylammonium bromide)

Abstract

Micelle formation in aqueous solutions of docosane- 1,22-bis(trimethylammonium bromide), referred to as C 22Me 6, has been investigated by means of conductivity, emf (concentration cell and bromide ion and detergent ion specific electrodes), density, light scattering, and fluorescence, as well as chemical relaxation (p-jump, T-jump, shock tube, ultrasonic absorption). The CMC, micelle ionization degree, micelle aggregation number, and volume change upon micellization have been found to be 2.8 × 10 −3 M, 0.38, 14, and 6 ± 2 cm 3/mole, respectively. The slope of the plot log CMC vs number m of carbon atoms in the alkyl chain of bolaforms of the C m Me 6 type as well as several other results reveal that these bolaforms behave like detergents with two charged groups on the first carbon of the alkyl chain. The main conclusion of the equilibrium studies is that the bolaform alkyl chain may be somewhat folded both in aqueous solution and in the micellized state. This conclusion is supported by the results of chemical relaxation studies which reveal for C 22Me 6 solutions relaxation times orders of magnitude smaller than those of the singly charged homolog. Upper limit values for the rate constants k − and k + for the dissociation and association of a bolaform to and from a micelle have been found to be 7 × 10 6 sec −1 and 2 × 10 9 M −1 sec −1. These values are not compatible with an extended conformation of the micellized bolaform alkyl chain.