Freedericksz Transition Measurements on Polymer-Stabilized Liquid Crystals

Abstract

Electric-field Freedericksz transition experiments were performed on homogeneous nematic samples of pentylcyanobiphenyl in which an anisotropic cross-linked polymeric network was formed. The studied geometry yields the splay elastic constant from the threshold voltage, Vc. Specimens in which the network was polymerized with the field OFF exhibited an increase in Vc; those in which the network was formed with the field ON, i.e. in the homeotropic alignment, showed a decrease in Vc. These observations are interpreted in terms of a model which assumes that the nematic elasticity is coupled to that of the network. Thus, Vc depends on the longitudinal component of the network elasticity, as well as on the Frank elastic constant. From this relationship, values of network elastic modulus can be estimated.

Key Words:

• Polymer stabilized liquid crystal
• Freedericksz transition
• splay elastic constant
• network elasticity