Ishino Katsuma, Shingai Hajime, Hikita Yasuyuki, Yoshikawa Isao, Houjou Hirohiko, Iwase Katsunori
DENSO CORPORATION, 500-1 Minamiyama, Komenoki-cho, Nisshin, Aichi 470-0111, Japan.
Institute of Industrial Science, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505, Japan.
ACS Omega. 2021 Nov 22;6(48):32869-32878. doi: 10.1021/acsomega.1c04866. eCollection 2021 Dec 7.
The cold crystallization mechanism of 1-{[4'-(4″-nitrophenylazo)phenyloxy]}hexyl-3-methyl-1-imidazol-3-ium tetrafluoroborate ionic liquid crystal was investigated based on thermal analysis, structural analysis, infrared spectroscopy, and quantum chemical calculations. By conducting thorough structural characterization, we found that the prerequisite for cold crystallization is the irreversible molecular conformational alteration induced by the initial heating of the as-grown crystal into a smectic liquid crystal. The originally linear cation molecule bends and forms a step-stair conformation that persists throughout the subsequent heating and cooling processes as phase transition occurs from the crystal phase to the liquid crystal phase and then to the isotropic liquid phase. The formation of cold crystal occurs because of the choice of molecular stability over crystalline stability. Given the exothermic anomaly exhibited upon heating generic crystals to cold crystals, these findings demonstrate the promising potential of this ionic liquid crystal for thermal energy storage applications.
基于热分析、结构分析、红外光谱和量子化学计算，研究了1-{[4'-(4″-硝基苯基偶氮)苯氧基]}己基-3-甲基-1-咪唑-3-鎓四氟硼酸盐离子液晶的冷结晶机理。通过进行全面的结构表征，我们发现冷结晶的前提是初生晶体初始加热转变为近晶型液晶时引起的不可逆分子构象改变。原本呈线性的阳离子分子弯曲并形成阶梯状构象，在随后从晶相到液晶相再到各向同性液相的相变过程中，整个加热和冷却过程中该构象都持续存在。冷晶体的形成是因为分子稳定性优于晶体稳定性。鉴于普通晶体加热到冷晶体时表现出放热异常，这些发现证明了这种离子液晶在热能存储应用方面具有广阔的潜力。
