EFFECT OF MOLECULAR STRUCTURES ON THE MESOPHASES AND MESOMORPHIC PROPERTIES OF CHIRAL LIQUID CRYSTALS

• Main Authors: Chang, Yung-Chi, 張永吉
• Other Authors: Wu Shune-Long
• Format: Others
• Language: zh-TW
• Published: 1996
• Online Access: http://ndltd.ncl.edu.tw/handle/91192066592648323135

碩士 === 大同工學院 === 化學工程學系 === 84 === ABSTRACT Two homologous series of chiral liquid crystalline materials derived fromoptically actives, (R)-(+)- and/or (S)-(-)-3- ethylmercapto-2-methylpropionic acids, have been synthesized. The investigation about the effect of molecular structures on the mesophases and mesoporphic properties were divided into two parts. The first part was to synthesize a homologous series of (S)-4-3- ethylmercapto-2-methylpropionyloxyalkyl)phenyl 4'-decyloxybiphenyl-4- carboxylates [(S)EMMPnP10BC; n=0-3] in order to understand the effect of increasing methylene length between the rigid core and the dipolar ester linkage on the mesomorphic properties. The second part was to synthesize a homologous series of (R)-6-(3-ethylmercapto-2- methylpropionyloxy)-2-naphthyl 4'-alkoxybiphenyl-4-carboxylates [(R)EMMPNmBC; m=6-13] in order to understand the effect of extending the rigid core structure by an additional phenyl ring and varying the periperal alkyl chain length on the formation of TGB phases. All homologues (S)EMMPnP10BC were mesomorphic, and had the phase sequences of Iso-SA*-SC*-S3*-K (n=0, 2, 3) and Iso-N*-SA*-SC*-K (n=1). The existence of the ferroelectric SC* phase was further confirmed by switching behavior and dielectric measurements. When the methylene spacers were introduced between the rigid core and the dipolar ester linkage, the thermal stability and the temperature range of the SC* phase depressed. In addition, the odd-even effect was obviously observed in some mesomorphic properties, such as the phase transition temperatures between mesophases, the direction of helix, the magnitudes of the spontaneous polarization (Ps) and the reduced polarization (Po). A positive sign of the Ps was found for all materials indicating that the direction of the spontaneous polarization was independent of the increasing methylene length. All homologous (R)EMMPNmBC were mesomorphic, and showed the phase sequences as follows: (R)EMMPN6BC:Iso-BPI-N*-TGBA*-SA*-K. (R)EMMPNmBC(m=7, 9-11):Iso-BPI-N*-TGBA*-SA*-SC*-K. (R)EMMPN8BC:Iso-BPI-N*-TGBA*-SA*-SC*-S4*-K. (R)EMMPN12BC:Iso-BPI-SA*-SC*-K. (R)EMMPN13BC:Iso-SA*-SC*-K. The existence of the novel TGBA* phase was further identified by contact method. When the rigid core structure was extended by an additional phenyl ring, the stability of the BPI and the TGBA* phase depressed,the TGBC* phase disappeared, and a relatively wide temperature range of the SC* phase was obtained. The formation of the mesophases was dependent on the peripheral alkyl chain length. The TGBA* phase was found as m<12. The stability of the BPI,N* and SA* phases depreased with the increasing peripheral alkyl chain length, whereas the temperature range of the SC* phase as m increased. Electro-optical study showed that the magnitudes of the Ps reduced as the rigid core structure was extended by an additional phenyl ring, and no correlation between the values of the Ps and the peripheral alkyl chain length was observed. The saturated apparent tilt angle ascended with the increasing peripheral alkyl chian length and then maintained at nearly the same values. In conclusion, various molecular structures indeed affected the formation of the mesophases and the mesomorphic properties. To realize the relationship between the molecular structures and the mesomorphic properties was helpful for the synthesis and application of the chiral liquid crystalline materials.