Phase behaviour of the thermotropic cubic mesogens 1,2-bis-(4-n-undecyl- and 4-n-dodecyl-oxybenzoyl)hydrazine under pressure

Abstract

The phase transition behaviour of two optically isotropic, thermotropic cubic mesogens 1,2-bis-(4-n-undecyloxy-and 4-n-dodecyloxy-benzoyl)hydrazine, BABH(11) and BABH(12), was investigated under hydrostatic pressures up to 300 MPa using a high pressure differential thermal analyser, a wide angle X-ray diffractometer and a polarizing optical microscope equipped with a high pressure optical cell. It is found that for BABH(11) and BABH (12), a smectic C (SmC) phase is induced between the isotropic liquid (I) and the cubic (Cub) phases by applying pressures above 10-12 and 16-17 MPa, respectively. A sea-island texture consisting of bright sand-like sea regions (SmC phase) and areas of dark islands (Cub phase) appears in the mesophase under pressures up to 140 MPa, while the sand-like texture of the SmC phase is formed predominantly on cooling under pressure. These observations indicate the destabilization of the cubic phase with increasing pressure. The phase transition sequence of BABH(11) and BABH(12), Cr-Cub-I at atmospheric pressure, changes to Cr-Cub-SmC-I under intermediate pressures and would change to Cr-SmC-I under elevated pressure.

New mesogen with thermotropic cubic phase: 3,4,5‐tris‐(11,11,12,12,13,13,14,14,15,15,16,16,16‐tridecafluorohexadecyloxy)benzoic acid

“…In these molecules, segregation of the incompatible groups is driven by the enthalpy of demixing, which leads to the formation of a distinct subspace with a minimal energy. Among the nonconventional LCs, thermotropic cubic phases, which represent ordered supermolecular arrangements and are optically isotropic, are attracting much interest due to their tremendous biological significance and potential application in drug delivery systems, etc, although the history of cubic phases dates from the first synthesis of nitrobiphenyl carboxylic acids by Gray in the 1950s [3][4][5][6][7][8][9][10][11]. Compared with the lyotropic cubic system, relatively few thermotropic compounds with isotropic cubic phases have been reported, although they have currently been recognized in a wider range of materials such as polyhydroxy molecules, dendritic molecules and metallomesogens; a cubic phase is often observed at relatively high temperature [12].…”