Cholesteric liquid crystal gels with a graded mechanical stress

Templated Twist Structure Liquid Crystals and Photonic Applications

Twist structure liquid crystals (TSLCs) have attracted increasing attention in photonic applications due to their distinct properties: Bragg reflection, scattering, and optical rotation. However, there exist some issues due to the defects of TSLCs: weak thermal stability, narrow bandwidth, and complicated fabrication. In this review, we introduce the templating technique which includes device structure, templating process, and photonic properties of templated TSLCs to improve the issues. Furthermore, a variety of photonic applications including lasing, optical filters and gratings based on TSLCs with polymer templates are presented. Additionally, other applications of TSLCs are briefly introduced. Finally, the remaining challenges and future perspectives of templated TSLCs are proposed.

Photo-Polymerization in Chiral Dopant Liquid Crystal Cells via Holographic Exposure to Fabricate Polarization-Independent Phase Modulator with Fast Optical Response

Small liquid crystal domains with random director distributions were obtained to show novel optical isotropy using a holographic exposure processes to treat chiral dopant liquid crystal cells in the isotropic phase (i.e., polymer-stabilized isotropic liquid crystal cells). The cells used to fabricate phase modulators showed unique performances, including low light scattering, polarization-independence, and fast optical response. Furthermore, an extra fluoro-surfactant dopant in cells showed that the phase modulators retained their performance but with considerable reduction of operating voltages, from 180 Vrms to 100 Vrms.

Optical thermal sensor based on cholesteric film refilled with mixture of toluene and ethanol

We demonstrate an optical thermal sensor based on cholesteric film refilled with mixture of toluene and ethanol. The thermal response mechanism is mainly based on the thermal expansion effect induce by toluene, where the ethanol is used for refractive index adjustment to determine the initial refection band position of cholesteric film. The ethanol-toluene mixture was used to adjust the color tunability with the temperature in relation with the habits of people (blue as cold, green as safe and red as hot). A broad temperature range of 86 °C and highly sensitivity of 1.79 nm/ °C are achieved in proposed thermal sensor, where the reflective color red-shifts from blue to red when environmental temperature increases from -6 °C to 80 °C. This battery-free thermal sensor possesses features including simple fabrication, low-cost, and broad temperature sensing range, showing potential application in scientific research and industry.

Broadening the reflection bandwidth of polymer-stabilized cholesteric liquid crystal via a reactive surface coating layer

We report a method of broadening the reflection bandwidth of polymer-stabilized cholesteric liquid crystal (PSCLC). The top substrate was consecutively coated with a polyimide (PI) and a reactive mesogen (RM) layer, while the bottom substrate was coated with only PI. We exposed the top substrate with the RM coating to UV light. The reflection bandwidth of the PSCLC samples where the top substrate was over-coated with RM was significantly broader than the samples where both substrates were coated with PI. In addition to the effect of the UV intensity gradient, the RM-coated top substrate has a chemical affinity to bulk RM, promoting formation of the pitch gradient and broadening the reflection bandwidth in the sample.