Stabilization and Destabilization of Thermotropic Liquid Crystalline Phases by Hydrogen Bondings

Six phase diagrams of liquid crystalline acids E and a phenole F mixed with derivatives of pyridine P, nicotinic acid Ni and pyrrolidine Py were investigated. Congruent melting compounds of the type PE and NiE were detected. Stabilization of the nematic and induction of a smectic A phase was observed in the P/E and P/F systems whereas in Py/E mixture an extremely strong destabilization of the nematic phase takes place. In the Ni/E diagrams a weak destabilization of the nematic phase was found. The results are explained by associates formed by hydrogen bridges which show a more or less strong deviation from the rod‐like molecular shape.