Effects of crosslinking agent, cure temperature, and UV flux on the electro‐optical properties of polymer‐dispersed liquid crystal cells

Abstract

We present results for the effects of a crosslinking agent, cure temperature, and UV flux on the electro-optical properties of polymer-dispersed liquid crystal (PDLC) cells. These cells were fabricated using a mixture of a liquid crystal (E8) and an acrylic monomer (CN135). The maximum in the first derivative of the transmission vs. applied, sinusoidal voltage (inflection voltage, V inf ), varies systematically with PDLC formulation and cure-process conditions. For PDLC cells fabricated with a crosslinking agent (SR295), V inf increases with increasing the concentration of SR295. However, for cells fabricated without the use of a crosslinking agent, V inf decreases with increasing the UV flux and decreasing temperature.

A review of the electro-optical properties and their modification by radiation in polymer-dispersed liquid crystals and thin films containing CdSe/ZnS quantum dots

“…10, we present data on relative light transmission as a function of applied ac electric field (at 2 kHz) and PDLC-irradiation by gamma-rays from 5 Ci 207 Bi. The transmission vs electric field data for un-irradiated cell are in excellent agreement with previously published results on similar PDLCs [30]. Transmission through the cell rises smoothly with increasing field; from being opaque at low electric fields to transparent at high electric fields.…”

“…It is well established by prior works, as well as by our recent publications that electro-optical properties of PDLCs can be influenced dramatically by the size and distribution of the liquid crystal droplets, which are controlled by several factors, e.g., concentration of the curing material, curing temperature, viscosity of the polymer, diffusion and solubility of the liquid crystal in the polymer, and the make-up of the starting solution. For example in a series of experiments, we have utilized recipes consisting of liquid crystal E8 (Merck), an acrylic monomer mixture consisting of tetrafunctional crosslinker (SR295), bisphenol diacrylate (SR349), UV photoinitiator (SR1124; 0.1 wt%) and 5-10 m diameter spherical ceramic particle spacers [30,31]. Results for the relative weight percentages of crosslinking agent (XL%) and liquid-crystal (LC%), and average LC droplet diameter for six different PDLC samples (Table 1).…”

“…It is now known that irradiating PDLCs with gamma-rays, as well as ultraviolet (UV) light brings about significant changes in the light transmission through the device because of irradiationinduced charges in the material [55]. Furthermore, the magnitude of the radiation-induced changes in the light transmission depends on the average size of LC droplets in the PDLC [30][31][32]. This contribution, to the most part, is a summary of our recent results on the optical properties of PDLC and CdSe/ZnS-based materials and is not meant to be a comprehensive review of the subject matter.…”

“…It may be possible to take advantage of the preferred properties of the polymer, liquid crystal, and semiconductor quantum dots and design a highly sensitive, cost-effective, and user-friendly radiation detector. It is precisely for this reason that we have been interested in the potential applications of these apparently two different classes of materials, PDLCs and CdSe/ZnS quantum dots for radiation detection [30][31][32]37,43,[51][52][53][54][55][56][57]. As the data presented in this review show the electro-optical properties of both the PDLCs and polymer films containing CdSe/ZnS quantum dots are sensitive to changes in the local electric fields brought about by the absorption of gammarays.…”

Holographically formed Bragg reflection gratings recorded in polymer-dispersed Liquid crystal cells using a He-Ne laser

“…The resulting refractive index modulation can be reversibly erased by applying an external electric field. For the synthesis of the H-PDLCs, as in our previous reports, [17][18][19] we utilized different mixtures of a polymerizable matrix and a thermotropic liquid crystal, E8 ͑Merck͒, with a nematic mesophase at room temperature ͑n e = 1.771, n o = 1.525, ⌬ = + 15.6͒. Photopolymerization of the monomers was initiated by means of a photoredox-catalysis mixture, consisting of a photo-oxidant dye ͑methylene blue͒ and coinitiator ͑p-toluenesulfonic acid͒ with concentrations of 0.12ϫ 10 −3 M and 0.21 M, respectively.…”