Advances in tuning the mechanoresponsive behavior of liquid crystal elastomers have facilitated the development of next‐generation applications such as reconfigurable photonic/electronic materials, energy‐harvesting devices, and flexible sensors. However, the molecular‐level control of mechanical responses remains difficult, with limited tunability achieved for recovery processes after stimulus removal. Herein, a design concept is proposed for facilely tuning the recovery of both the macroscopic deformation and molecular orientation change of liquid crystal elastomers using layered materials that exhibit the desired mechanoresponsive behavior. Changing the layering materials (a polydimethylsiloxane film with elastic response to a polymethylpenten film with plastic response) alters the relaxation time from <1 s to >6 months. To demonstrate this concept, highly sensitive, stretchable mechano‐optical sensors with fast and ultraslow recovery times are developed that enable an applied strain to be quantitatively detected in real time or memorized with high spatial resolution, even with a conventional camera. This material design concept for arbitrarily controlling the recovery response can provide a platform for stimuli‐responsive applications.
The rapid increase in demand for recyclable and reusable thermosets has necessitated the development of materials with chemical structures that exhibit these features. Thus, functional mesogenic epoxide monomers bearing both ester and imine groups that can be vitrimerized and recycled are reported herein. The compounds show mesophase characteristics at 100–200 °C and can be converted into hard epoxides by a common curing reaction. The obtained hard epoxides have high isotropic thermal conductivity (≈0.64 W m−1 K−1), which is derived from their highly ordered microstructures. The cured products can be easily reprocessed through imine metathesis and transesterification, and decomposed products can be obtained through imine hydrolysis under acidic or basic conditions and subsequently be re‐cured. Surprisingly, recycled materials can be repeatedly reprocessed or chemically decomposed. The reprocessed materials retain the properties of their pristine counterparts, and the recycled products preserve the advantages of the hard thermosets without alteration to any of their unique properties. A dehydration reaction occurs between the residual hydroxyl groups during the re‐hardening, which dramatically increases the glass transition temperature by ≈60 °C. These reprocessable and recyclable vitrimers demonstrate the effectiveness and environmental friendliness of the molecular design strategy reported herein.
In article number 2104702, Osamu Tsutsumi and co-workers report a multilayered concept for tuning the recovery response of cholesteric liquid crystal elastomers, enabling a stretchable, sensitive mechano-optical sensor with on-demand spatiotemporal resolution. The mechanical strain imposed on the sensor can be visualized and quantified using a commercially available camera as well as the naked eye.
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