Fan-shaped, toric and spherulitic textures of mesomorphic oxadiazoles

Abstract

When a family of non symmetrical heterocycled compounds is investigated, a variety of mesophases can be observed with rather different features. Here we report the behaviour of seven different members among a family of such materials, that consists of mesomorphic oxadiazole compounds. In two of these compounds, the optical microscope investigation shows very interesting behaviours. In their smectic phases, fan-shaped and toric textures, sometimes with periodic instability, are observed. Moreover, the nematic phase displays a texture transition. Texture transitions have been previously observed only inside the nematic phase of some compounds belonging to the families of the oxybenzoic and cyclohexane acids. In these two oxadiazole compounds we can observe what we define as a "toric nematic phase", heating the samples from the smectic phase. The toric nematic texture disappears as the sample is further heated, changing into a smooth texture.

Some Features of Liquid Crystalline Oxadiazoles

“…The optical microscope investigations show very interesting behavior of the smectic and the nematic phase of some of these oxadiazole compounds [13]. In particular the smectic phases have a toric texture that changes in a spherulitic nematic.…”

“…Figure 6 shows the transition between the smectic and the spherulitic nematic of compound C of Ref. 13 (here simply called ODBP). The figure shows the smectic (a) and the lowtemperature (b) and the high-temperature (c) nematic phases.…”

ChemInform Abstract: A Survey of Liquid Crystalline Oxadiazoles

“…The examples we can find in the references that we have previously reported, show that not only the chemical structure of the substituents, but also their position with respect to the oxadiazole ring is relevant for the mesophases. The optical microscope investigations show very interesting behaviour of the smectic and the nematic phase of some of these oxadiazole compounds [13]. In particular the smectic phases have a toric texture that transform in a spherulitic nematic.…”

“…Fig.6 shows the transition between the smectic and the spherulitic nematic of compound C of Ref. 13 (here simply called ODBP). The figure shows the smectic (a) and the low-temperature (b) and the high-temperature (c) nematic phases.…”

Growth of toric domains in mesophases of oxadiazoles

“…In a previous paper [1], hereafter referred as I, we investigated a family of mesomorphic oxadiazoles with asymmetrical molecular structures. The family consisted of oxadiazoles [2][3][4], containing terminal Cl-group and phenyl-cyclohexane fragment together with biphenyl analogues.…”