Study on the Mesomorphic and Physical Properties of Chiral Liquid Crystals Containing Optically Active (L)-Lactate Group

• Main Authors: Hung-Jui Lin, 林泓叡
• Other Authors: Shune-Long Wu
• Format: Others
• Language: en_US
• Published: 2007
• Online Access: http://ndltd.ncl.edu.tw/handle/jxyvw9

碩士 === 大同大學 === 化學工程學系(所) === 95 === It is generally acknowledged that optically active lactic acid as chiral source for the preparation of chiral liquid crystals has outstanding mesomorphic and electro-optical propertiesm, such as (i) having wide temperature range of SmC* phase, (ii) the SmC* phase temperature is closed to the room temperature and (iii) having high spontaneous polarization (Ps value). In this work, we designed and synthesized chiral liquid crystal materials, as shown bellow, by using (S)-(-)-lactate as the initial material, for the investigation of mesomorphic and electro-optical properties. The phase sequences, transition temperatures and corresponding phase transition enthalpies of mesophase measured by DSC and optical microscope. The experimental result shows that compounds I (m=9, 11) are mesomorphic, and the mesomorphic phase sequences and transition temperatures are as follows: I (m=9): Iso (138.88℃) N* (133.07 ℃) SmA* (106.17℃) SmC* (76.33℃)Cr1 (69.1℃) Cr2, I(m=11):Iso (143.06℃) N* (137.35℃) SmA* (111.47℃) SmC* (74.29℃) Cr1.(54.82℃) Cr2 The results show that compounds I (m=9, 11) exhibit enantiotropic mesophases of the N*, SmA* and SmC* phases. An increasing nonchiral peripheral alkoxy chain lengths ‘m’ increased the Iso-N*, N*-SmA* and SmA*-SmC* transition temperatures but lower SmC*-Cr1 transition temperature. Temperature range of the SmC* phase increased with the increasing carbon chain length. The results of electro-optic properties in these two materials have been demonstrated to exhibit ferroelectricity in SmC* phase by a single peak switching current of the switching behavior. The maximum spontaneous polarization (Ps value) of compounds I (m=9) in ferroelectric SmC* phase reaches 32 nC/cm2, and the maximum optical tilt angle reaches 18°. The maximum spontaneous polarization (Ps value) of compounds I (m=11) in ferroelectric SmC* phase reaches 100 nC/cm2, and the maximum optical tilt angle reaches 19°. The results show that increasing nonchiral peripheral alkoxy chain lengths ‘m’ increased spontaneous polarization (Ps value) and apparent tilt angle under the temperature of Tc .In conclusion, the results from above indicate that the nonchiral peripheral alkoxy chain length indeed have the significant effect on the stability of SmC* phase.