Cubic Phases of 4'-n-docosyloxy-3'-nitrobiphenyl-4-carboxylic Acid (ANBC-22)

Abstract

Dilatometric experiments have been performed on 4 0 -n-docosyloxy-3 0 -nitrobiphenyl-4-carboxylic acid (ANBC-22) which exhibits two types of thermotropic cubic phases (Cub I and II) on heating. Although the unit lattices of both Cub I and II, determined by X-ray diffraction measurements, slightly but certainly shrink with increasing temperature, the thermal expansion coefficients in both temperature regions were found to be positive. Thus, this study provided an experimental evidence that the number of molecules constructing the unit lattice of the two Cub phases decreases with temperature. Some aspects of the structural features of the Cub phases are discussed.

Smectic C to Cubic Phase Transition of 4′-n-Docosyloxy-3′-nitrobiphenyl-4-carboxylic Acid (ANBC-22) and Alternating-Current Electric Field Effect

“…Two different points between the two systems are: (i) the symmetry of the Cub phase structure in the present compound is Im3m, and this type of bicontinuous Cub phase is limited in the thermotropic LCs at this stage; 1d,e,g and (ii) the aggregation structures in the present compound are built up by one kind of molecules, about 6000 molecules per unit lattice. 6 In connection with the second point, in the above lyotropic systems, it is most probable that mobile water molecules would assist a much faster completion of the process than in the present case. Regarding the first point, on the other hand, whether the highly restricted nucleation uncovered in the present work is really characteristic of the formation of the Im3m-Cub phase from the SmC phase remains to be clarified.…”

“…In contrast, in the present compound, the process is very slow and the τ value at a temperature 4 K above the true transition temperature (i.e., 400.5 K) is on the order of several hundreds of minutes (Figure a). Two different points between the two systems are: (i) the symmetry of the Cub phase structure in the present compound is Im 3 m , and this type of bicontinuous Cub phase is limited in the thermotropic LCs at this stage; ,, and (ii) the aggregation structures in the present compound are built up by one kind of molecules, about 6000 molecules per unit lattice . In connection with the second point, in the above lyotropic systems, it is most probable that mobile water molecules would assist a much faster completion of the process than in the present case.…”

“…Here, M is the molar mass of ANBC-22 (= 567 g mol −1 ), ρ is the density (= 0.990 g cm −3 ), Δ SmC−Cub H m is the molar transition enthalpy (= 2 kJ mol −1 ), , and ε 0 is the vacuum permittivity (= 8.854 × 10 −12 C 2 m −2 N −1 ). From our preliminary dielectric studies, it was shown that |ε Cub − ε SmC | ≤ 0.1 at 10−100 kHz (see Figure S2 of the Supporting Information), and thus, we can roughly estimate |Δ T | ≤ 0.005 K for E = 100 000 V cm −1 .…”

“…The cubic (Cub) mesophases have attracted great attention because of their self-organization of simple rodlike molecules into a complex aggregation structure with cubic symmetry . 4′- n -Docosyloxy-3′-nitrobiphenyl-4-carboxylic acid (ANBC-22, where “22” represents the number of carbon atoms in the alkoxy group) is such a Cub phase-forming compound. ,– It exhibits the following phase sequence upon heating: Smectic C (SmC) → Im 3 m -Cub → Ia 3 d -Cub → isotropic liquid . The low-temperature three phases are considered to be basically made up by layered aggregates of the ANBC-22 molecules, but having different degrees of dimensionality; the SmC phase is a one-dimensionally ordered phase, whereas the two Cub phases are three-dimensionally ordered ones.…”

“…The low-temperature three phases are considered to be basically made up by layered aggregates of the ANBC-22 molecules, but having different degrees of dimensionality; the SmC phase is a one-dimensionally ordered phase, whereas the two Cub phases are three-dimensionally ordered ones. The Ia 3 d -Cub phase is widely seen in thermotropic and lyotropic liquid crystals (LCs) and block copolymers, often called gyroid, but the Im 3 m -Cub phase is at present limited in the thermotropic LCs. ,, The phase transition behavior has been investigated by several techniques such as differential scanning calorimetry (DSC), adiabatic calorimetry, polarizing optical microscopy (POM), dynamic viscoelasticity (DVE), , and X-ray diffraction (XRD) . Nevertheless, like other soft materials, little is understood about the transition kinetics and detailed mechanisms of the transformation from the SmC to Cub phases and from one Cub phase to another.…”