Electron Beam Curing of Monomer/Liquid Crystal Blends

Abstract

This chapter focuses on a comparison of two polymerization/crosslinking methods to produce polymer/liquid crystal (LC) systems: rapid UV-visible irradiation and high voltage accelerated electron beams (EB), with comparable exposure times. The comparison was performed in terms of some physical properties such as phase diagrams, polymerization and phase separation kinetics, morphologies, and electro-optical responses. During polymerization and crosslinking, the longer the spacing between the two acrylic double bonds or the higher the molecular weight, the more rapid was the monomer conversion under UV-light; however, the reverse was found for EB-curing. The PDLC films produced by EB curing had more homogenous and regular morphologies. The electro-optical responses of various PDLC systems showed significant differences between the UV-cured samples and those cured by EB. It was found that the driving voltages considerably increased in the case of the UV-cured systems. For the contrast ratios, which are important for applications, EB-cured systems confirm their higher quality. Moreover, EB curing leads to considerable monomer conversions without a photoinitiator which may act as an impurity that might have negative impact on the electro-optical performance of the obtained PDLC films.

End-of-Life Liquid Crystal Displays Recycling: Physico-Chemical Properties of Recovered Liquid Crystals

“…By making a suitable choice of components of the mixture, it is possible to obtain a transparent film when the system is subjected to a sufficient electric voltage ("on" state) and opaque in the absence of voltage ("off" state). These materials are of interest for their many applications, especially in the field of electroactive glazing and display devices [31][32][33][34].…”

Temperature Controlled Mechanical Reinforcement of Polyacrylate Films Containing Nematic Liquid Crystals

“…The effects of both radiation dose and dose rate on the preparation of UV-and EBcured polymer and polymer/LC films were investigated by Bouchakour et al [12,13] on TPGDA/E7 and other similar acrylic systems. Polymerization and crosslinking reactions of monomer/LC mixtures may introduce phase separation processes that are likely to govern sample morphologies of the obtained polymer/LC films.…”

“…In particular, the decrease in the FTIR-bands associated with the carbon-carbon double bonds of the acrylate groups were followed (C=C deformation band at 810 cm −1 , and another C=C valence vibration around 1638 cm −1 ), as a function of a radiation dose. It was found that increasing the radiation doses lead to an increase in the acrylic double bond conversion [13]. The LC E7 acts as a solvent and the polymerization reaction was governed by the diffusion of the initiator radicals in this solvent towards the acrylic double bonds.…”

“…The electron beam (EB) technique has the advantage of enabling the curing process to be carried out in the absence of any initiating species and is not sensitive to UV-absorbent materials, for example dyes. This technique has already been applied to elaborate polymer films and Polymer Dispersed Liquid Crystals (PDLC) materials [9][10][11][12][13]. Starting from a homogeneous mixture with a low molecular weight LC, and the reactive monomer(s), radiation induced polymerization/crosslinking processes lead to a decrease in the miscibility between the LC and the growing polymer network, with the mixture finally separating into two phases.…”

Estimation of Ionic Impurities in Poly(propylene Glycol) Diacrylate Monomers/Liquid Crystal E7 Mixtures Using Dielectric Spectroscopy

“…Three acrylic polypropylene glycol diacrylate (PPGDA) monomers were used, with reactive chains of different molecular weights between their two acrylic end groups. These materials were chosen because they have already been studied in the UMET laboratory and present interesting electro-optical, thermophysical, and mechanical properties [26][27][28].…”