MCP 184-2016-197

Effect of temperature on the morphology and electro-optical
properties of liquid crystal physical gel

Liquid crystal physical gels were (thermally) prepared with cholesteryl stearate as a gelator in nematic
liquid crystal, 4-cyano-40-pentylbiphenyl. The electro-optical performance of liquid crystal physical gels
is almost entirely dependent on the gels’ inherent morphology. This study involved an empirical
investigation of the relationships among all of the gelation temperature, morphology, and electro-optical
properties. Besides continuous cooling at room temperature, isothermal cooling was also performed at
both 18 and 0 C, corresponding to near-solid and solid phases of 4-cyano-40-pentylbiphenyl respectively.
Nevertheless, the liquid crystal physical gel was also isothermally rapidly cooled using liquid nitrogen.
Polarizing optical microscopy showed that the gel structure became thinner when isothermal cooling
was carried out. These thinner gel aggregates then interconnected to form larger liquid crystal domains.
Moreover, it was also revealed that the gel networks were randomized. Electron spin resonance results
showed that the liquid crystal director orientation was severely randomized in the presence of gel
networks. Conversely, isothermal cooling using liquid nitrogen generated a higher liquid crystal director
orientation order. The 6.0 wt% cholesteryl stearate/4-cyano-40-pentylbiphenyl physical gel that was
isothermally cooled using liquid nitrogen showed the lowest response time in a twisted nematic mode
optical cell.