Preparation and Characterization of Normal and Reverse Mode Polymer Dispersed Liquid Crystals

Abstract

Polymer dispersed liquid crystals (PDLCs) have become an area of interdisciplinary newlineresearch and developing their great scientific attention in this field. In PDLCs, liquid newlinecrystal (LC) is trapped as drops embedded within a polymeric matrix and LC molecules newlinewithin droplets are randomly aligned parallel to the substrate and scattered light in OFF newlinestate. However, in reverse mode PDLC, LC is vertically aligned (VA) initially and newlinetransparent in OFF state. Thus, research work was focused to prepare normal and reverse newlinemode PDLCs and studied their droplet morphology, electro-optic (EO) characteristics, newlinethreshold and operating voltages, contrast ratio (CR), response time and absorption newlinebehaviour as well as interdependency among all these parameters. Initially, Introduction newlineof LC to PDLCs along with process cum formation of normal and reverse modes was newlinestudied and reviewed the advancements in the field extensively. Further, normal mode newlinePDLCs for conventional (pure) and with the doping of silica nanoparticles (NPs) and newlinemultiwall carbon nano tubes (CNTs) were prepared and investigated in detail. Results newlinehave shown that NPs and multiwall CNTs in PDLC readily controlled the molecular newlineorientation and dynamics of LC in droplets with reduced value of threshold electric field newlinein addition to higher contrast. Further, work was continued with the effect of doping of newlineazo orange dichroic dye having varied concentrations (0.0625%-1.0% of LC) in PDLCs newlinewere prepared and characterized. Experimental results showed that controlled amount newlineof azo orange dichroic dye reduce the scattering with the alignment of the LC molecules newlinealong the director and showed enhanced EO characteristics as compared to conventional newlinenormal mode PDLCs. Moreover, the effect of NPs and dye in reverse mode PDLCs was newlinealso observed. Consequently, in reverse mode PDLCs, the POM study confirmed the newlinedevelopment of VA of LC within the LC droplets. Droplet configuration varies with newlineapplied voltage and showed the scattering state with radially planar type textures. newlineDoping of N