Multiple light scattering in polymer dispersed liquid crystals: A Monte Carlo simulation

Abstract

Polymer dispersed liquid crystals (PDLC's) are non-homogeneous materials consisting of liquid crystal (LC) droplets randomly distributed in a polymer matrix. Light incident on the PDLC undergoes multiple scattering along the boundaries of the matrix and the LC droplets making the PDLC viable for window shutter and light modulator applications. Because light scattering is the main mechanism that governs the optical behavior of PDLC films, it is essential that a model describing the scattering behavior of the film be formulated.
Diffusion theory and random walk simulations have been utilized to describe light propagation through PDLC layers. However, their validity is limited to highly scattering and isotropic cases. The treatment has been extended to include large droplet sizes but is limited to single scattering. Most PDLC systems consist mainly of nematic LC droplets, each having a random director configuration within the polymer matrix. For large droplet diameters and high LC concentration, the bulk sample becomes highly anisotropic and cannot be described using diffusion analysis. In this paper, we utilize a Monte Carlo (MC) model to trace the photon trajectories inside the layer. The model possesses several advantages: 1) it can incorporate droplet concentration and size, 2) it can accommodate complex optical configurations without the need to satisfy complex boundary conditions and 3) it can incorporate particle anisotropy. In particular, the MC model is utilized to investigate the angular dependence of transmitted light for varying LC concentration and droplet size, in the presence of sample refractive index mismatch.