The Effect of the Degree of Polymerization and Polymer Composition on the Temperature Responsiveness of Cholesteric Semi-Interpenetrating Networks

Cholesteric liquid crystal oligomers and polymers are promising materials for creating materials and devices with stimuli-responsive structural color, and the cholesteric to smectic pre-transition effect is of particular interest as it leads to a strong redshift in the reflected color upon cooling. Cholesteric polymers can be stabilized by the formation of semi-interpenetrating networks to obtain more robust photonic materials, but this tends to strongly suppress the pre-transition effect. Here, we show that the pre-transition effect in semi-interpenetrating networks based on main-chain cholesteric oligomers can be amplified by incorporating a smectic monomer and by increasing the degree of polymerization of the oligomers. This amplification counteracts the suppressing effect of the semi-interpenetrating network, and the resulting materials still show a significant band shift upon cooling. Presumably, both methods lead to the formation of more smectic domains in the cholesteric helix, which causes an amplified pre-transitional effect. The results bring us closer to the use of cholesteric semi-interpenetrating cholesteric networks for applications in smart sensing, healthcare, and safety devices.