ALKANEDIYL-ALPHA,OMEGA-BIS(DIMETHYLALKYLAMMONIUM BROMIDE) SURFACTANTS .1. EFFECT OF THE SPACER CHAIN-LENGTH ON THE CRITICAL MICELLE CONCENTRATION AND MICELLE IONIZATION DEGREE

The critical micelle concentration (cmc) and micelle ionization degree (alpha) of the title surfactants, C(s)H2s-alpha,omega-((CH3)2N+C(m)H2m+1Br-)2, in aqueous solution have been investigated as a function of the numbers s and m of carbon atoms of the alkanediyl spacer and of the alkyl chain, respectively. The cmc of the surfactant series with m = 12 and 16 has been found to go through a maximum of small amplitude for s = 5 +/- 1, irrespective of the length of the alkyl side chain. At constant s, log cmc decreases linearly upon increasing m with the same slope as monoquaternary ammonium surfactants. The changes of alpha with s and m are qualitatively similar to those found for monoquaternary ammonium surfactants with one or two alkyl chains, previously investigated. The changes of cmc have been interpreted in terms of conformation changes of the surfactant ion and of progressive penetration of the spacer in the micelle hydrophobic core upon increasing s.