Investigation of bulk properties and monolayer behaviour of amphiphilic mesogens: structural variations of the head group

Non-ionic amphiphilic compounds—butane-1.2,3-triol derivatives, 2-hydroxycarboxylic acids and carboxylic acids—incorporating rigid aromatic structural units like 1,4-disubstituted benzene, 4,4′-disubstituted biphenyl or the 2-phenyl-1,3,4-thiadiazole have been prepared. In most cases these compounds exhibit smectic liquid crystalline phases which can be stabilized by the addition of water. Their mesomorphic properties are compared with those of the structurally related 1,2-diol derivatives. Surprisingly, also some ω-(4-alkylphenoxy)alkanoic acids which have no thermotropic mesophases were found to aggregate to lyotropic mesophases in the presence of water. Most of the new compounds form stable monolayers at the air–water interface. The force–area isotherms of the thiadiazole derivatives have been recorded and it was found that they strongly depend on the chemical structure of the head group.