Phase behaviour of the thermotropic cubic mesogen 1,2-bis(4-n-decyloxybenzoyl)hydrazine under pressure

Abstract

The phase transition behaviour of an optically isotropic, thermotropic cubic mesogen 1,2-bis(4-n-decyloxybenzoyl)hydrazine, BABH(10), was investigated under pressures up to 300 MPa using a high pressure differential thermal analyser, a wide angle X-ray diffractometer and a polarizing optical microscope (POM) equipped with a high pressure optical cell. The reversible change in structure and optical texture between the cubic (Cub) and smectic C (SmC) phases was associated with a change from a spot-like X-ray pattern and dark field for the Cub phase to the Debye-Sherrer ring pattern and sandlike texture for the SmC phase under both isobaric and isothermal conditions. The Cub phase was found to disappear at pressures above about 11 MPa. The phase transition sequence, low temperature crystal (Cr 3 )-intermediate temperature crystal (Cr 2 )-high temperature crystal (Cr 1 )-Cub-SmC-isotropic liquid (I) observed at atmospheric pressure, is maintained in the low pressure region below 10 MPa. The transition sequence changes to Cr 3 -Cr 2 -(Cr 1 )-SmC-I in the high pressure region. Since the Cub-SmC transition line determined by POM has a negative slope (dT/dP) in the T-P phase diagram, a triple point is estimated approximately at 10-11 MPa, and 143-145 ‡C for the SmC, Cub and Cr 1 phases, giving the upper limit of pressure for the observation of the cubic phase.

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

“…Figure 2 shows the X-ray pattern of the cubic phase of BABH (12) at 150 ‡C in the cooling mode at atmospheric pressure. The spotlike reflections indicate a polydomain structure, as already seen for the cubic phases of BABH(8) and BABH(10) [25,26]. The pattern of diffraction spots of the cubic phase is very similar to that for BABH (8) which reduced to the {2 1 1} and {2 2 0} reflections of the cubic phase with space group Ia3d [16].…”

“…This clearly reveals the pressure-induced formation of the SmC phase and is the same texture as observed in BABH(8) and BABH(10) [25,26]. The bright islands grow rapidly with decreasing temperature, figures 7 (c) and 7 (d ), and coalesce to form the homogeneous sand-like texture of the SmC phase at 157 ‡C, figure 7 (e), although small black spots randomly placed of the cubic phase remain.…”

“…In other words, the Cub-SmC transition in BABH (8) and BABH(10) may be explained using the ClausiusClapeyron equation. The molar volume is estimated to decrease at the CubpSmC transition [25,26]: the molar volume of the high temperature SmC phase will be smaller than that of the low temperature cubic phase, i.e. V SmC vV Cub .…”

“…The authors have reported the phase behaviour of BABH (8) and BABH(10) under pressure using a high pressure differential thermal analyser (DTA) and a polarizing optical microscope (POM) equipped with a high pressure optical cell, and determined the T vs. P phase diagram in the heating mode [25,26]. Since only the Cub-SmC transition line of all the phase boundaries has a negative slope (dT/dP) in the T-P phase diagram, the temperature range for the cubic phase decreases rapidly with pressure.…”

Aqueous-Phase Behavior of Natural Glycolipid Biosurfactant Mannosylerythritol Lipid A: Sponge, Cubic, and Lamellar Phases

“…35 Maeda et al also reported that the spotty ring patterns are observed from the space group Ia3d of the bicontinuous cubic phase. 36 Although no clear sharp peak was observed in the diffractogram (see Figure 3b, left-hand side), the reciprocal spacings of the first and second Bragg peaks were found to be in the ratio 6:…”