Polymer Dispersed Liquid Crystals (PDLC) are composite materials consisting of small liquid crystal (LC) droplets surrounded by a polymer matrix. Due to their relatively easy preparation and processing, the PDLC devices found many applications such as displays, architectural windows, energy control devices, projection displays, spatial light modulators, polarizers.
Carbon nanotubes (CNT) have excellent mobility and are suitable as doping nanoparticles in order to improve the electrically- controlled orientation of LC.
This paper presents the methods of preparation of PDLC doped with CNT. Experimental results are presented for the films obtained by solvent induced polymerization method, using polymethyl methacrylate and a nematic LC, E7. The obtained films are characterized by polarized optical microscopy, differential scanning calorimetry and electro-optical transmission.
The investigation of light propagation in the polymer dispersed liquid crystal film in its isotropic phase is carried out. The propagation of coherent (direct) component of the transmitted and reflected light in the film with high concentration of spherical scatters is considered by using the adding method. The calculation results of coherent transmittance, reflectance, and phases of transmitted and reflected waves are presented.
A method for calculation ellipsometrical parameters of light transmitted through a polymer dispersed liquid-crystal film is proposed. It is based on the Rayleigh-Gans approximation for independent scattering regime. Functional dependencies of ellipticity and azimuth of polarization ellipse of scattered light on liquid-crystal droplets' order parameter are presented.
A method for calculating transmission coefficient and characteristics of polarization state of light transmitted through polymer film with fine liquid crystal droplets is proposed. It is based on the Rayleigh-Gans approximation to describe scattering by an individual droplet, and the Foldy-Twersky equation to determine a coherent field transmitted through the polymer dispersed liquid crystal film. The results obtained relate the morphological characteristics of a film to its electro-optical response. The simple equations for scattering cross-sections are obtained. The accuracy of the method is estimated.
The optical method to retrieve order parameter of liquid crystal droplets with rigidly fixed poles has been developed. The method is based on measurement of coherent transmittance of a monolayer of polymer-dispersed liquid crystal droplets and comparison with the results of coherent transmittance calculation. To calculate coherent transmittance of a polymer -dispersed liquid crystal monolayer the anomalous diffraction approximation and the approximation of effective refractive indexes for liquid crystal droplets are used.