Effect of multilactate chiral part of liquid crystalline molecule on mesomorphic behaviour

Mesomorphic behaviour of several series of materials derived from the lactic acid has been studied and their physical properties have been compared and summarized. These compounds with the same molecular core differing by the linkage group of the non-chiral chain possess a broad variety of liquid crystalline phases: the paraelectric SmA, the ferroelectric SmC∗, the antiferroelectric SmC∗A, the re-entrant SmC∗re, the ferroelectric hexatic phases and a monotropic low temperature phase. The antiferroelectric phase occurs in materials with two lactate groups only, where the ether or the keto group is used as linkage between the non-chiral chain and molecular core. The studied homologues with one, three or even four lactate groups do not exhibit the antiferroelectric phase, but possess a broad range of the SmA and SmC∗ phases down to room temperatures. The presence of the keto group increases the temperature range and values of the spontaneous polarisation of polar liquid crystalline phases. Molecules with the ether or keto group have a different distribution of electron densities, which seems to be responsible for the difference in the mesomorphic properties. The relationship between the molecular chain structure and mesomorphic properties of lactic acid derivatives with particular molecular core forming the polar mesophases are discussed.