Diminution of Even-Odd Alternation in Smectic-Nematic Transitions

Abstract

The alternation in Smectic A-Nematic transition temperatures of the members of a homologous series is generally observed to be highly diminished and in some cases even absent, as compared to the Nematic-Isotropic transition temperatures. The earlier mean field model by some of the present authors showed on the contrary, an enhancement. This inadequency of the earlier model has been removed in this paper by explicitly taking into account a variation of McMillan's α parameter from member to member. The phase diagrams for the first seven members of the PAA series and of 4-(4′-n-2-(4′-n-alkoxy-benzylideneamino) biphenyls are presented which demonstrate the diminution. Further, some results of a model system are presented to bring out the fact that the diminution is actually due to the variation of α. A faster variation of α causing a steeper rise in A-N temperature entails a greater dampening of alternation.

Key Words:

• Smectic-Nematic transitions
• chain molecules