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(dimethylalk ylammonium 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 vani shes at s = 10 and 12, for which micelles are present at all compositi ons 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 exist ence of a lamellar phase and of a cylindrical phase with the surfactan t 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.