Abstract
We synthesized tetrafunctional allyl ether monomer (4-AE) and investigated the effects of the different molar ratios of trimethylolpropane tris-(3-mercaptopropionate) (3-SH) to 4-AE on the photopolymerization behavior, morphology, and electro-optical properties of thiol-ene-based PDLC films. Photo-DSC and DSC analyses revealed that the PDLC sample containing 45 wt% 3-SH and 45 wt% 4-AE gave the highest exotherm, the fastest photocure rate, and the highest Tg due to the matched stoichiometry. Morphological observations and electro-optical measurements showed that the PDLC sample with the matched molar ratio gave the smallest LC droplet size, the highest threshold, driving voltages, and lowest saturation transmittance because the orientation of LC molecules got difficulty in small droplets. The stoichiometric ratios of 3-SH to 4-AE played an important role in controlling the photocure rate, phase separation rate, microstructures of LC droplets, and electro-optical properties of thiol-ene-based PDLC systems.
Highlights
Polymer dispersed liquid crystal (PDLC) is a composite containing low-molecular-weight liquid crystal (LC) domains randomly dispersed within a continuous polymer matrix
We investigated the effects of the molar ratio of thiol-ene monomers on the photopolymerization-induced phase separation process, morphology, and PDLC performances
PhotoDSC and DSC analyses revealed that the PDLC sample containing 45 wt% 3-SH and 45 wt% 4-AE gave the highest exotherm, the fastest photocure rate, and the highest Tg due to the matched stoichiometry
Summary
Polymer dispersed liquid crystal (PDLC) is a composite containing low-molecular-weight liquid crystal (LC) domains randomly dispersed within a continuous polymer matrix. The LC directors are oriented in the direction of the electric field within the LC domains, which matches the refractive index of the polymer matrix to that of the ordinary component of the LC, and the PDLC film appears transparent. In the step-growth polymerization, the increase in molecular weight is much slower and the gelation takes place at a higher degree of monomer conversion These intrinsic properties of thiol-ene systems enable the PDLC films to be produced with a uniform morphology with narrow dispersity in the shape and size of LC droplets and a higher degree of LC phase separation. We investigated the effects of the molar ratio of thiol-ene monomers on the photopolymerization-induced phase separation process, morphology, and PDLC performances
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