Phase Transitions of 4‘-n-Hexacosyloxy-3‘-nitrobiphenyl-4-carboxylic Acid (ANBC-26):  Two Types of Thermotropic Cubic Phases

Abstract

The phase transitions of 4′-n-hexacosyloxy-3′-nitrobiphenyl-4-carboxylic acid (ANBC-26, where "26" indicates the number of carbon atoms in the alkoxy group) were investigated by differential scanning calorimetric (DSC), polarizing optical microscopic, and X-ray diffraction (XRD) measurements. ANBC-26 is a new liquid crystalline material which exhibits successively two types of three-dimensionally ordered cubic mesophases on heating; the low-temperature cubic (CubI) phase has a space group of Im3m, and the high-temperature one (CubII phase) is of Ia3d type, identical with the cubic phase of shorter alkoxy chain homologues such as ANBC-16, and a cubic-cubic phase transition occurs at 435 K on DSC. Reversibility of the transitions between them was studied and the structures of those mesophases are discussed. The transformation from a onedimensionally ordered smectic C (SmC) to the CubI phase and to the CubII phase can be interpreted qualitatively in terms of the increased curvature of the interface. The structured liquid I 1 phase, an intermediate phase between the CubII and a true isotropic liquid I 2 phases, has been also studied, indicating that this phase could be characterized by Ornstein-Zernike type short-range fluctuation, which means the presence of molecular clusters consisting of several ANBC-26 dimers in the temperature region.

AFM, X-ray Diffraction and Optical Microscopy Studies of Faceted Droplets of a Thermotropic Bicontinuous Cubic Mesophase

“…More details concerning the synthesis will be published elsewhere. [8] As expected, we succeeded in decreasing the clearing temperatures as shown in Table 1 (typical clearing temperatures of ANBC compounds having linear chains are around 200 8C [1] ). Moreover, compared with the ANBC derivatives bearing a linear chain, we obtained, in all cases, mesomorphic compounds although the chains are shorter.…”

“…[1] Two kinds of these phases can be found, micellar or bicontinuous, of different space groups. Concerning the bicontinuous mesophases, several models are now well accepted.…”

“…Indeed, with the ANBC derivatives having linear chains, enantiotropic mesophases exist for n 16 to 26. [1] Finally, as described in Table 1, the mesophase can be kept for all compounds until room temperature, as previously described in ref. [3], which gave us the opportunity to study the obtained facets by AFM.…”

Discotic liquid crystals of transition metal complexes 37* : a thermotropic cubic mesophase havingPnmsymmetry exhibited by phthalocyanine‐based derivatives

“…Cubic mesophases are categorized into two systems: thermotropic system and lyotropic system. Thermotropic cubic mesophases are shown by rod-like molecules, dendrimers and polycatenars [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16], whereas lyotropic cubic mesophases are shown by lipid-solvent system and so on [17][18][19][20][21][22]. Each of the compounds exhibiting both two kinds of cubic mesophases consists of two incompatible parts: an aliphatic chain and an aromatic core or a polar group and a nonpolar group.…”

“…Rod-like molecules and polycatenars of thermotropic system tend to exhibit a bicontinuous cubic mesophase with Im3 n symmetry. When the interface curvature between the incompatible parts is small in lyotropic system, bicontinuous cubic mesophases tend to be formed with Pn3 have been well revealed for their symmetries [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16]. Thus, the investigation of these thermotropic cubic mesophases has been greatly progressed.…”