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Cholesteric liquid crystals (CLC) are molecules that can self-assemble into helicoidal superstructures exhibiting circularly polarized reflection. The facile self-assembly and resulting optical properties makes CLCs a promising technology for an array of industrial applications, including reflective displays, tunable mirror-less lasers, optical storage, tunable color filters, and smart windows. The helicoidal structure of CLC can be stabilized via in situ photopolymerization of liquid crystal monomers in a CLC mixture, resulting in polymer-stabilized CLCs (PSCLCs). PSCLCs exhibit a dynamic optical response that can be induced by external stimuli, including electric fields, heat, and light. In this review, we discuss the electro-optic response and potential mechanism of PSCLCs reported over the past decade. Multiple electro-optic responses in PSCLCs with negative or positive dielectric anisotropy have been identified, including bandwidth broadening, red and blue tuning, and switching the reflection notch when an electric field is applied. The reconfigurable optical response of PSCLCs with positive dielectric anisotropy is also discussed. That is, red tuning (or broadening) by applying a DC field and switching by applying an AC field were both observed for the first time in a PSCLC sample. Finally, we discuss the potential mechanism for the dynamic response in PSCLCs.

An autonomous and continuously operating Radio Frequency Identification (RFID) temperature sensor is designed, manufactured, and tested. This sensor is battery-free and can detect temperature threshold crossings for multiple (room-to-cold and cold-to-room) temperature cycles, respectively. The proposed sensor conveys temperature threshold crossings through the controlled switching of its operating frequency within the 902-928 MHz Ultra High Frequency (UHF) RFID band. For the first time, shape morphing cold-temperature reactive Liquid Crystal Elastomers (LCEs), which provide reversible actuation, are utilized. The proposed sensor design consists of a patch antenna with a customized slot. A passive mechanical switch is connected across this slot and provides the frequency switching as it is activated and deactivated. The integration of this switch with the antenna is achieved using a co-simulation method. Furthermore, the cold-temperature reactive LCE triggers the switch when a temperature violation has occurred, thereby switching the operating frequency of the sensor based on temperature changes. Additionally, a high-dielectric constant substrate and a single matching network that operates at two discrete frequencies are used to design our compact frequency-domain temperature sensor. Moreover, based on the RFID platform, this sensor operates effectively in close-proximity to other sensors. Also, is provides identification and temperature information through an autonomous, continuous, and cost-effective design. Therefore, the proposed sensor has the potential for operation in the Internet of Things (IoTs) applications, where large amounts of data is collected from numerous sensors to extract valuable information for the benefit of users, manufacturers, and delivery companies in the virtual domain of the internet. Finally, ANSYS HFSS and Circuit Designer are used for the simulation modeling. The performance of our sensor is validated using measurements and simulations that agree very well.

In this research, we have developed a novel temperature sensor to be utilized in the Cold-Supply-Chain (CSC) for perishable items. This sensor conveys temperature threshold crossings by switching operation between two individual RFID ICs, i.e., two individual Electronic Product Codes (EPCs). The advantage of this sensor compared to other existing technologies is that it can operate passively (i.e., battery-free) through multiple room-to-cold and cold-to-room temperature cycles, in real-time, without requiring any form of resetting. This design utilizes innovative cold-responsive liquid crystal elastomers (LCEs), which change shape when stimulated by cold temperatures and returns to a relaxed state when the stimulus is removed. In fact, this is the first temperature sensor that conveys temperature threshold crossings by switching between two RFID ICs using LCEs. The correct operation of the sensor is validated by RFID measurements. ANSYS HFSS and ANSYS Circuit Designer were used for the simulation analysis. The performance of the proposed design was validated using simulations and measurements.

Stimuli-responsive materials that exhibit a mechanical response to specific biological conditions are of considerable interest for responsive, implantable medical devices. Herein, we report the synthesis, processing and characterization of oxidation-responsive liquid crystal elastomers that demonstrate programmable shape changes in response to reactive oxygen species. Direct ink writing (DIW) is used to fabricate Liquid Crystal Elastomers (LCEs) with programmed molecular orientation and anisotropic mechanical properties. LCE structures were immersed in different media (oxidative, basic and saline) at body temperature to measure in vitro degradation. Oxidation-sensitive hydrophobic thioether linkages transition to hydrophilic sulfoxide and sulfone groups. The introduction of these polar moieties brings about anisotropic swelling of the polymer network in an aqueous environment, inducing complex shape changes. 3D-printed uniaxial strips exhibit 8% contraction along the nematic director and 16% orthogonal expansion in oxidative media, while printed LCEs azimuthally deform into cones 19 times their original thickness. Ultimately, these LCEs degrade completely. In contrast, LCEs subjected to basic and saline solutions showed no apparent response. These oxidation-responsive LCEs with programmable shape changes may enable a wide range of applications in target specific drug delivery systems and other diagnostic and therapeutic tools.