Influence of azo dye on dielectric and opto-electronic properties in polymer-liquid crystal composite structures

In this thesis, the dielectric, electro-optic, morphological and thermal properties of Azo Dye Methly Red (MR) with different concentrations of doped Polymer Dispersed Liquid Crystal (PDLC) structure were investigated. Pure and dye doped PDLC composite structures were prepared using E63 coded nematic liquid crystal, Norland 65 polymer and MR at ratio of 1%, 3% and 5% wt/wt by Polymerization-Induced Phase Separation (PIPS) technique. Dielectric properties of composite structures were investigated in the frequency range of 500 Hz-10 MHz at room temperature using dielectric spectroscopy method. Parameters such as the real and imaginary parts of complex dielectric constant, dielectric anisotropy, loss tangent, relaxation frequency, crossover frequency, threshold voltage, splay elastic constant and relaxation time of pure and dye doped PDLC composite structures were obtained using experimental data. Moreover the response time, rise time and fall time were obtained using optic-transmittance system. The absorbance, dichroic ratio and the order parameter of MR dye in liquid crystal were investigated using UV–VIS Spectrophotometer. The phase transition temperature of composites was noted through polarizing optical microscopy and differential scanning calorimetry. The values of important parameters such as threshold voltage and relaxation time were decreased whereas liquid crystal droplet sizes were increased with increasing MR concentration. Results show that dispersing MR in PDLC composite structure causes significant changes in the dielectric and opto-electronic properties and the dye doped PDLC composite structures will be suitable and promising functional materials for liquid crystal based devise applications.