Surface polymer-stabilized dual frequency chiral liquid crystals

Abstract

Polymer-liquid crystal (LC) composite materials provide cost-effective ways to achieve enhanced electro-optic functionalities. Corresponding bulk-dispersed and phase-separated (of various degrees) morphologies were intensively studied in the past and are shortly described in this work. In addition, we consider the specific case when the polymer-LC structures are formed near to the cell substrates. To achieve this, partially cured and oriented polymer coatings are used as alignment layers for dual frequency chiral LC. The partial curing is intended to allow a partial interpenetration between the LC and the polymer molecules to form surface-stabilized polymer networks. After a short interpenetration period (between the polymer coatings and the bulk LC), a positive dielectric torque is applied and UV exposition is used to definitely cure the material system. Our electro-optical, spectroscopic and microscopic studies show that the pre-curing duration plays a crucial role in the behavior of the cell. It is shown that the molecular interdiffusion generates defects of LC alignment around polymer aggregates on the cell's internal surfaces. The obtained out-of-plane alignment and small polymer aggregates are at the origin of formation of controllable light scattering. Among others, some linear defects are formed by the positive torque, which are, however, eliminated when a negative dielectric torque is applied.

Keywords:

• chiral liquid crystals
• reactive mesogen
• photopolymerization
• pretilt
• scatter
• defects

Acknowledgements

We acknowledge the financial support of NSERC, Canada.