Smectic and cubic mesophases of alkylammonium poly(vinylsulfonate)s

The thermotropic liquid crystal behavior of n-alkylammonium, N,N-dimethyl-n -alkylammonium, and quaternary N,N-dimethyl-N-cyanopropyl-n-alkylammonium p oly(vinylsulfonate)s was investigated using differential scanning calorimet ry, polarizing optical microscopy, and X-ray diffraction. All the hexadecyl and octadecyl derivatives exhibit a smectic B phase at low temperature and a smectic A phase at high temperature. The dodecyl and tetradecyl derivati ves of the first two series exhibit a smectic A phase at all temperatures e xplored, from ambient up to thermal degradation. The dodecyl and tetradecyl derivatives of the third series show a smectic B phase at high temperature and, quite interestingly, an Ia3d body-centered-cubic phase at low tempera ture. The structure of the cubic phase consists of molecular bilayers bent according to Schoen's gyroid minimal surface. Sitting directly on the minim al surface, the polar heads of the molecules cover the same area in the cub ic as in the adjacent smectic phase. The transition from cubic to smectic w as briefly discussed.