NOVEL SMECTIC POLYMORPHIC BEHAVIOUR IN HOMOLOGOUS SERIES OF MESOGENS

Abstract

The high alternation of nematic thermal stabilities found in the series of o-phenyl- alkyl4-(4'-phenylbenzylideneamino) cinnamates as the homologous series was ascended has been further exaggerated by substituting the terminal phenyl ester ring with methyl or chloro substi- tuents in the 3- or 4-positions. Nematic phases were found only when an even number (n) of methylene units occurred in the alkylene chain. Srnectic thermal stabilities also alternated as each of the four series of esters was ascended. Howe- ver, the srnectic A thermal stabilities decreased and the smectic B thermal stabilities increased on passing from even to odd values of n. In some cases this caused the thermal stabilities of the smectic A and B phases to coincide for odd values of n. When this occurred, a unique texture was observed microscopically at the I-S transition. Although no SA-SB transition could be detected microscopi- cally or by D. T. A., miscibility studies indicated that a transitional SA phase still existed. This suggests that it is necessary to form a transitional SA phase intermediate between the amorphous liquid and a SB phase, both on heating and cooling. This transition has been called SAB-I. Smectic E phases were also found for many of the sixteen new esters, and the thermal stabilities of SE phases, like those of SB phases, increased for odd values of n. The relative effects of 3- and 4-methyl- and chloro-substituents on N, SA, Sn and SR thermal stabilities are discussed.