Study On Electro-optical Properties Of Silica Particles Doped Polymer Dispersed Liquid Crystal

The presence of excellent film- forming, mechanical strength, thermal stability and unique electro-optical properties related to liquid crystal orientational and positional order at the same time, make polymer d ispersed liq uid crystals(PDLC) popular applied in the optical functional devices, including the following: flat panel displays, optical attenuators, holographic gratings, voltage sensors, electro-chromic devices, smart electric windows, solar energy harvestings, etc. In order to improve physical properties of PDLC, the early research focus on different kinds of nano-particles to the PDLC system, and it is desirable to improve the PDLC performance.The Si O 2 nano- particles is one of the most common doped particles.A series of S i O 2 nano-particles were prepared in this paper, which are the spherical Si O2 particles with three different sizes, rod- like Si O 2 particles and two different surface modification(APTES modification and VTES modification) spherical Si O 2 particles. Then the different concentrations of the above mentioned Si O2 nano-particles were doped into the PDLC of E7/NOA65 system. Finally, Fourier Tra ns for m Infrared spectroscopy(FTIR), D ifferent ia l Scanning C alorimetr y(DSC), Scanning Electron Microscopy(SEM) and the Electro-optical analysis(E-O) were used to test these S i O 2 nano-particles doped PDLC, to analyze the effect of different conce ntrat ions, differe nt s izes, differe nt shapes and different s ur face- modified part icles doped Si O2 on morpholo gy a nd electro- optical properties of the PDLC.Different concentrations of spherical Si O 2 particles with the same size were added into the PDLC,testing results show that the interaction between the spherical Si O 2 particles and LC E7 is weak, and has no effect on the t her modyna mics of the LC E7. However, doping spherical S i O 2 particles with different concentrations has large influence on the morphology of the PDLC. At the same time, different concentrations of doped spherical Si O2 particles has a great influence on the PDLC electro-optical properties, with the increase of the doping concentration, the PDLC transmittance decreases, threshold voltage increases and the contrast ratio increases. Different sizes of spherical Si O 2 particles with the same concentration were added into PDLC, testing results show that, the interaction between the different sizes of spherical S i O 2 particles and LC E7 is also weak, and has no effect on the ther modyna mics of the LC E7. However, different sizes of doped spherical S i O 2 particles have great influence on the PDLC morphology, especially the size and distribution of the LC E7. The electro-optical performance will also depend on the size of doped spherical Si O2 particles.Different concentrations of rod-like Si O 2 particles with the same size were added into PDLC,testing results show that, the interaction of the rod- like S i O2 particles and LC E7 is so small, and has no effect on the t her modyna mics of the LC E7. However, doping spherical S i O 2 particles with different concentrations has a large influence on morphology of the PDLC, as the concentrations of rod- like Si O2 particles increases, the LC E7 droplets in PDLC are more dense and uniform, the electro-optical performance of PDLC is also improved, mainly increas ing the contrast ratio. Comparing the spherical S i O 2 particles with the rod- like Si O 2 particles doped PDLC,the results show that, the interaction between the different shapes of Si O 2 particles and LC E7 is also weak, and have no effect on the ther modyna mics of the LC E7. But different shapes of doped S i O 2 particles make size and shape distributions of LC E7 really different. Meanwhile, the rod- like particles Si O 2 doped PDLC has lower transmittance but higher contrast ratio than that of the spherical particles Si O 2 doped the PDLC.Differe nt concentrat ions o f the APTES modified spherical S i O 2 partic les and the VTES modified spherical S i O 2 particles were added into the PDLC,testing res ults show t hat, t he interact ion of t he modified spherical S i O 2 partic les and LC E7 is so small, but has large effect on the therma l stability of the LC E7, this effect has litt le relat io nship w it h the doping concentrat io n. PDLC doped with d ifferent concentratio ns of the APTES modified spherical Si O 2 particles and the V TES mod ified spherical Si O 2 particles ha ve different morpho logy. As the concentrat io ns of modified spherical S i O 2 partic les increases, PDLC transmittance decreases, the contras t ratio increases, and the threshold voltage increased small. Comparing the modified Si O 2 particles with nonmod ified Si O 2 particles doped PDLC, the results show that, doping modified Si O 2 particles has lar ge effect on the ther mal stability of the LC E7,b ut nonmod ified has litt le effect. Further more, the morphology and electro-optical properties are different.The threshold voltage and the contrast ratio are important parameters for the PDLC, we can improve the electro-optical properties of the PDLC through doping a variety of nano-Si O 2 particles. In the production and experiment, in order to obtain excellent PDLC materials, we must consider the threshold voltage and contrast and other factors, to select the appropriate concentration, size, shape, and sur face modification of nano-Si O 2 material.