The Studies Of Flexible Tricolor LC Cells Based Polymer Dispersed Cholesteric Liquid Crystal

Flexible displays have drawn much attention because of their lighter weight, thinnerpackaging, flexibility, and high portability. Their potential applications involve wearablecomputers, smart cards, and different design patterns for displays. As the substrates used inflexible display are flexible plastic films, it is quite suitable for a cost-effective roll-to-rollprocess. This dissertation dealed with the fabrication of flexible tricolor liquid crystal (LC)cells using a polymer dispersed LC (PDLC) method in which the LC is quasi-solidified byencapsulating in a polymer matrix. A cholesteric LC is chosen for tow main reasons. Onone hand cholesteric LC can work in reflective mode which make the polarizer andbacklight are not necessary in LC cell. On the other hand, as cholesteric LC has bistablestates, image can keep even when no power is supplied and only the refreshing of thescreen requires a driving voltage, which means a much less power-consumption inchloesteric LC display than conventional nematic LC display. The work has been dividedinto three parts.Firstly, morphology of PDLC and electro-optic properties have been studied. Polymerdispersed liquid crystal (PDLC) films are prepared by means of ultraviolet (UV) inducedphase separation. The effects of UV cure power and UV cure temperature on morphologyof PDLC have been studied in detail, the relationship between morphology of PDLC andreflectivity has also been studied. The results show that high monomer concentration allowssmall LC domains and nonuniform disperse. Low UV cure power allows complete phaseseparation, large LC domains size and smooth interface between polymer and LC. StrongUV cure power results in a rough interface which also decreases the size of LC domains.But the relationship of PDLC morphology and UV cure temperature is complex. At lowUV cure temperature LC dispersed as circular droplets in polymer matrix. The size of LCdomains become bigger which yield adjacent and uniform layers of LC and polymer whenthe UV cure temperature is up to40°C. Higher UV cure temperature causes a type ofthree-dimensional polymer network structure in which LC is dispersed. Differentmorphology of PDLC cause varying degrees of interaction between polymer and LCdomains, and then obtains different electro-optic properties.Secondly, the fabrication of flexible tricolor LC cells has been studied includingelectrode etching and cell-filling processl. As PET plastic films was used to replace theorigin rigid glass substrates for preparing flexible LC cells, the traditional cell-filling process causes nonuniform thickness and traps air bubbles in LC cells which deterioratesproperty of flexible LC device. These problems are effectively solved by using aroller-laminating technique. The processing temperature is critical. Heating up the cell canreduce the viscosity of LC and, thus avoed the interfusion of air bubbles in the solution.Thirdly, the passive matrix drive of flexible tricolor LC cells has been studied. In orderto achieve red, blue and green display, different chiral concentration has been added.Finally, flexible tricolor LC display for suitable driving is able to exhibit information evenwhen it is bent.