Liquid crystalline complexes of an azo-containing surfactomesogen with oppositely charged polyelectrolytes

A triethyl-ammonium functionalized 4-nitro-4′-alkoxy azobenzene mesogen with a 10-carbon spacer (azo10Q, a ‘surfactomesogen’) was complexed in equimolar proportions to a variety of oppositely charged polyelectrolytes, and studied by differential scanning calorimetry (DSC), polarizing optical microscopy, and X-ray diffraction. The complexation generates a single-layer smectic A mesophase over a very wide temperature range from a surfactomesogen that, alone, melts directly to the isotropic phase. The clearing temperatures, ranging from 130 to 190 °C and generally higher than the melting point of azo10Q, are dependent on the nature of the polyelectrolyte as well as its molecular weight. In contrast, a prominent glass transition near ambient temperature appears to be independent of molecular weight, but varies somewhat with the type of polyelectrolyte. A second T_g-like transition of much lower intensity is detectable at higher temperatures (generally above 100 °C), and, with literature support, is tentatively attributed to nanophase separation involving sublayer planes in the lamellar packing structure. A series of nonequimolar complexes was also investigated, and it was found that, with decreasing azo10Q content, the clearing temperature viewed by DSC decreases rapidly in intensity (and somewhat in temperature) and then disappears although birefringence remains, whereas the lower glass transition increases rapidly in temperature to finally merge with the upper one. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3421–3431, 2005