ALKANEDIYL-ALPHA,OMEGA-BIS(DIMETHYLALKYLAMMONIUM BROMIDE) SURFACTANTS .2. STRUCTURE OF THE LYOTROPIC MESOPHASES IN THE PRESENCE OF WATER

The mesomorphic behavior of the alkanediyl-alpha,omega-bis(dimethylalkylammonium bromide) surfactants, referred to as m-s-m (where s is the number of carbon atoms in the polymethylene chains connecting the two CmH2m+1N+(CH3)2Br- moieties), has been investigated by DSC, polarizing optical microscopy, and X-ray diffraction. The concentration range of the lyotropic mesophases decreases as s increases and completely vanishes at s = 10 and 12, for which micelles are present at all compositions up to 90 wt % of surfactant. Lyotropic mesophases again occur for s = 16. In this respect, the 12-s-12 surfactants behave very similarly to the two-chain/one-headgroup 12-s/2. The detailed investigation of the lyotropic behavior of the 12-8-12 homologue has revealed the existence of a lamellar phase and of a cylindrical phase with the surfactant alkyl chains inside the cylinders. The structural parameters of the two phases have been determined, showing the connecting octamethylene chains to lie consistently within the interfaces.