Reorientational Steepness of Nematic Liquid Crystal Enhanced by Adding Side Chain Type Liquid Crystalline Polymer.

The ratio of bend to splay elastic constant K₃/K₁ of the nematic directer is an important parameter because it determines the steepness of the response between homogeneous or twist alignment and homeotropic alignment. A smaller K₃/K₁ means sharper threshold response. K₃/K₁ varies with the ratio of both the length and width of a liquid crystalline molecule, and the short range ordering in the nematic phase. Addition of side chain liquid crystalline polymer (LCP) to the nematic liquid crystal is expected to increase the short range ordering in the lateral dirbction of molecule, and then to induce the short range smectic-like ordering. The aim of this study is to enhance the steepness of electric response of a nematic liquid crystal by adding the side chain type LCP. It was a short range smectic-like ordering was induced even in the nematic phase in the case that the side chain type LCP was molecularly dispersed in the low molecular weight liquid crystalline phase. As the molar fraction of the side chain type LCP increased, the ordering increased, the magnitude of K₃/K₁ decreased, and the significantly sharper threshold characteristic was achieved in the nematic phase. This result is applicable for the control of the electric response characteristic of a nematic liquid crystal display.