Smectic mesophases from dihydroxy derivatives of quaternary alkylammonium salts

A series of N,N-di(2-hydroxyethyl)-N-methyl-N-alkylammonium bromides (alkyl chain from dodecyl to octadecyl) was synthesized and characterized. Its th ermotropic liquid-crystal behaviour was studied by differential scanning ca lorimetry, polarizing optical microscopy, infrared spectroscopy and X-ray d iffraction. Two smectic phases were identified, an ordered smectic T and a disordered smectic A phase. Both phases result from an alternate periodic s tacking of polar sublayers of ionic head groups and apolar sublayers of alk yl chains in a disordered conformation. In the low-temperature smectic T ph ase, the ionic head groups are arranged inside the polar sublayers in a par ticularly dense fashion, a tetragonal crystal lattice. In the high-temperat ure smectic A phase, the ionic head groups are arranged in a disordered fas hion with normal packing density.