Light transmission through polymer film with nanosized liquid crystal droplets: theoretical study

Abstract

ABSTRACT Model of light transmission through a polymer-dispersed liquid crystal film with nanosized nematic droplets at oblique and normal illumination is presented. The model is based on the Rayleigh-Gans approximation describing light scattering by a single droplet and the Foldy-Twersky equation taking into account multiple scattering. Dependences of extinction, phase shift, and polarization state of light on the applied electric field are considered. The theoretical results are compared with the available experimental data. Keywords: Nanosized droplets, liquid crystal composites, light modulation, polarization of light, PDLC films. 1. INTRODUCTION In recent decades, a big deal of attention has been given to new promising liquid crystalline materials: polymer dispersed liquid crystal (PDLC) films, due to wide range of their possible applications [1-5]. Of particular interest are PDLC films with nanosized liquid crystal (LC) droplets. These films possess weak light scattering and enable one to change polarization state of transmitted light by varying electric field applied to the film. These properties can be successfully applied in designing various electrooptical devices with controllable optical characteristics. In itself a PDLC film is a thin polymer film with embedded LC droplets [2, 3]. This film is placed between two transparent plates with deposited transparent electrodes. When a voltage is applied to the electrodes, molecules of LC inside droplets change their orientation. Thus optical properties of a PDLC film are changed. It enables one to modulate light transmitted through the film. In present work we develop a theoretical model of light transmittance through a PDLC film with small partially oriented nematic droplets. The model allows establishing a link between morphological properties of the PDLC film and characteristics of transmitted light. The LC molecules reorientation under the applied voltage is described using multilevel order parameter concept.