Morphology effect on the light scattering and dynamic response of polymer network liquid crystal phase modulator

Abstract

Polymer network liquid crystal (PNLC) was one of the most potential liquid crystal for submillisecond response phase modulation, which was possible to be applied in submillisecond response phase only spatial light modulator. But until now the light scattering when liquid crystal director was reoriented by external electric field limited its phase modulation application. Dynamic response of phase change when high voltage was applied was also not elucidated. The mechanism that determines the light scattering was studied by analyzing the polymer network morphology by SEM method. Samples were prepared by varying the polymerization temperature, UV curing intensity and polymerization time. The morphology effect on the dynamic response of phase change was studied, in which high voltage was usually applied and electro-striction effect was often induced. The experimental results indicate that the polymer network morphology was mainly characterized by cross linked single fibrils, cross linked fibril bundles or even both. Although the formation of fibril bundle usually induced large light scattering, such a polymer network could endure higher voltage. In contrast, although the formation of cross linked single fibrils induced small light scattering, such a polymer network cannot endure higher voltage. There is a tradeoff between the light scattering and high voltage endurance. The electro-optical properties such as threshold voltage and response time were taken to verify our conclusion. For future application, the monomer molecular structure, the liquid crystal solvent and the polymerization conditions should be optimized to generate optimal polymer network morphology.

Optimization of the electrospun-aligned microfiber composite with liquid crystal for terahertz wave variable phase shifters

“…Previous studies have reported that THz wave phase shifters using LC have either a tiny phase change 17) or a excessively long decay time due to the thick LC layer of several hundreds of micrometers or more. [18][19][20][21] As effective methods for improving the decay time, polymerstabilized LC (PSLC) [22][23][24][25][26][27][28][29][30] and nanofiber (NF)/LC composite 31,32) have been employed. In the PSLC, reactive bifunctional monomers with a small amount (<10 wt%) are mixed into the LC and crosslinked to each other after polymerization.…”

“…33) However, previous studies have reported that the PSLC threshold voltage rises by several tens of volts, even in the thickness of only a few tens of micrometers. 25,26,29) In another example for a device at THz frequency, where the decay time was significantly shortened to a few tens of milliseconds, an enormous voltage of approximately 900 V was employed to obtain a phase change of 30°. At that time, the composite showed 55% of the natural ability in the THz birefringence of LC.…”