Polymer dispersed liquid crystals in the IR dichroic and non-dichroic wavelength analysis

Abstract

Polymer dispersed liquid crystals (PDLCs) are composite materials of LC droplets dispersed in a polymer binder. These materials can be used effectively to modulate infrared (IR) light in the 2.5 to 14.0 μm region.
PDLCs fabricated frgm E7:PVP on Pt-coated NaCl subtrates were characterized using IR angular discrimination techniques. Results generated transmission-wavelength and transmission-orientation profiles for discrete droplet sizes in the 2 to 40 μm range. Numerical modeling methods using the Fresnel equations, Beer-Lambert law and the Rayleigh-Gans-Zumer approximations were then used to simulate the spectrophotometric plots. Dichroic effects and phase change factors due to induced birefringence produced better curve fits and optical constants (n_o, n_e, Δn) of PDLCs in the IR. Refractive indices of the PDLC system for 3.13, 4.0, 5.0, 9.2 and 10.8 μm incident IR radiation using (2-3) μm and (12-25) μm droplet sizes are generated and reported. Listed with previous data for 2.5, 8.3 and 14.3 μm IR wavelength, the refractive indices and birefringence in the 2.5 to 14.3 μm are thus completed.
Non-dichroic wavelengths showed decreasing n_o and n_e, for increasing wavelengths with a constant birefringence of ~0.20. Dichroic wavelengths (8.3, 9.2,10.8 μm) have large n_e values with an average birefringence of ~0.25. The refractive indices of the polymer binder (PVP) show the same decreasing n_o and n_e values for increasing wavelength.