Cubic D Phase of 4′-n-Pentadecyloxy-3′-Nitrobiphenyl-4-Carboxylic Acid

Abstract The phase behavior of 4′-n-pentadecyloxy-3′-nitrobiphenyl-4-carboxylic acid (ANBC-15, where “15” corresponds the number of carbons in the alkoxy groups) was investigated by differential scanning calorimetric, polarizing optical microscopic, infrared spectroscopic and dynamic viscoelastic (DVE) measurements. ANBC-15 has a critical alkoxy chain length for exhibiting the cubic D (CubD) phase in ANBC series, and the virgin sample of ANBC-15 shows the CubD phase on heating, but the appearance of the CubD phase in the second heating depends on the turnover temperature of the preceding heating. Such instability of the CubD phase was also observed by isothermal frequency scans of DVE, which reveals the existence of a crossover of the storage and loss modulus curves, reflecting a structural fluctuation of the CubD phase in ANBC-15. The instability of the CubD phase of ANBC-15 is suppressed by mixing 25 mol % of ANBC-16, resulting in an enantiotropic CubD phase.