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Cholesteric liquid crystals (CLCs) exhibit Bragg reflection due to their spontaneous self-assembly into a one-dimensional photonic structure. Retaining this cholesteric order in a polymer network requires functionalizing liquid crystals with reactive end groups. However, conventional chemistries for synthesizing cholesteric liquid crystalline polymers often result in poor surface alignment and reduced optical quality. In this work, we investigate a thiol−ene step-growth polymerization approach to fabricate cholesteric liquid crystalline elastomers (CLCEs) with tunable mechanical properties and improved optical quality. By varying the cross-link density, we systematically study the effects on haze, cross-linking degree, and mechanical response. Compared to existing cholesteric liquid crystalline polymers, the thiol−ene-based CLCEs exhibit enhanced surface alignment, reduced haze, and greater mechanical tunability. These materials are further benchmarked against CLCEs synthesized via thiol−acrylate chain transfer polymerization, highlighting the advantages of the thiol−ene reaction for achieving precisely controlled properties in cholesteric polymer networks. 

Cholesteric liquid crystalline elastomers (CLCEs) exhibit selective reflection due to a periodic variation of the refractive index throughout the thickness of the material. CLCEs can be formulated and prepared to reflect light in the UV, visible, and infrared regions of the electromagnetic spectrum by simply adjusting the concentration of the chiral species. This report details the synthesis and preparation of appropriately thick CLCEs that maximize reflection in both the short-wave and mid-wave infrared (SWIR, MWIR) regions of the electromagnetic spectrum. As elastomers, fully solid CLCEs can be mechanically deformed to tune the selective reflection. This report details approaches to tune selective reflection, including mechanical deformation, incidence angle, thermochromism, and dielectric actuation. Generally, the optomechanical response of the CLCE at longer pitch lengths (e.g., infrared reflecting) is comparatively less than that of prior examinations of analogous compositions with a shorter pitch. Furthermore, the contribution of modulus and dielectric breakdown to electromechanical response is examined. 

Liquid crystalline elastomers (LCEs) prepared via thiol−ene photopolymerization result in homogeneous distribution of molecular weight between cross-links. Numerous prior reports emphasize that LCEs are material actuators that undergo a thermomechanical response associated with an order−disorder transition. However, modern and widely utilized approaches to create LCEs result in heterogeneous networks. Theoretical examination suggests that network heterogeneity and high degrees of cross-linking cause a continuous association of strain with temperature, rather than a first-order, stepwise association. Alternatively, thiol−ene photopolymerization historically yields homogeneous polymers with tailorable cross-link densities. This report extends these prior studies to formulations, which are conducive to LCE preparation. Specifically, this examination copolymerizes a liquid crystalline dialkene mesogen with a tetrathiol cross-linker and dithiol chain extender via a purely thiol−ene polymerization. Notably, this composition is amenable to surface-enforced alignment. This contribution exploits the tunability of thiol−ene photopolymerization to emphasize the influence of cross-linking on the coupling of strain and temperature.