Science Diliman, Vol 13, No 2 (2001)

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Multiple Light Scattering in Polymer Dispersed Liquid Crystals: A Monte Carlo Simulation

Serafin Delica, Carlo Mar Blanca

Abstract


Excerpt

Polymer dispersed liquid crystals (PDLC's) are nonhomogeneous 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 (Commander et aI., 2000; Kelly et aI., 2000). 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 (Neijzen et aI., 1997). However, their validity is limited to highly scattering and isotropic cases (Uvera & Durian, 1996). 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, making the sample highly anisotropic. In this paper, we utilize a Monte Carlo (MC) model (Blanca & Saloma, 1999) to trace the photon trajectories inside the layer. The model possesses several advantages: (I) 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.

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