Photopolymerization Kinetics And Properties For Composites Of Polymer Dispersed Liquid Crystal And Titania By In Situ Sol-gel Method

Polymer dispersed liquid crystal can be used in many areas such as switching, smartwindow, holographic materials. With the development of laser holography technology,holographic polymer dispersed liquid crystals (HPDLC) arise at the historic moment. Thebasic principle of HPDLC is the polymerization of monomers under light irradiation andthe phase separation induced by photopolymerization. The performance of HPDLC mainlydepends on the degree of phase separation, volume shrinkage and refractive index contrast.In this dissertation, the titania nanoparticles in the dispersions of acrylate monomer(AM) or in the mixture of AM and liquid crystal (LC) are synthesized by in situ sol-gelmethod. The photo-differential scanning calorimetry (P-DSC) was used to characterize thephotopolymerization kinetics by changing the temperature, the UV light density and thecontent of titania nanoparticles. The volume shrinkage has been studied by density methodand rheology method separately. The main results were as follows.1. The homogeneous dispersions of titania nanoparticles in acrylate monomers couldbe prepared by controlling the pH, the ratio of water and titania precursor. The diameter ofmonodispersed nanoparticles was about20nanometers.2. The maximum rate of photopolymerization (Rp,max) of the dispersions of titania/AMand the final monomer conversion (αFinal) obviously increased with the increase oftemperature and UV light density. Both Rp,maxand αFinalwere almost independent on thecontent of ethanol. However, with increase of the content of titania, the Rp,maxdecreasedapparently and the αFinalhad a certain decline.3. The addition of titania nanoparticles significantly reduced the volume shrinkage ofacrylate systems about42.4%which was investigated by density method. The volumeshrinkage was studied by rheology method as well. The experimental data of volumeshrinkage were different from the different methods, but the values decreased with theincrease of the content of titania for both methods.4. The Rp,maxand αFinalfor the dispersions of titania/AM/LC increased with the increaseof content of titania nanoparticles obviously.5. For the thin films of polyacrylate dispersed liquid crystals containing titania nanoparticles, the threshold voltage and saturation voltage were reduced but the contrastincreased. Unfortunately, the content of titania was only below3wt%.