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Poly-(N -isopropylacrylamide) (PNIPA) hydrogel films doped with uniaxially aligned liquid crystalline (LC) nanosheets adsorbed with a dye are synthesized and its anomalous photothermal deformation is demonstrated. The alignment of the nanosheet LC at the cm-scale is easily achieved by the application of an in-plane or out-of-plane AC electric field during photo-polymerization. A photoresponsive pattern is printable onto the gel with μm-scale resolution by adsorption of the dye through a pattern-holed silicone rubber. When the gel is irradiated with light, only the colored part is photothermally deformed. Interestingly, the photo-irradiated gel shows temporal expansion along one direction followed by anisotropic shrinkage, which is an anomalous behavior for a conventional PNIPA gel. [ABSTRACT FROM AUTHOR]

Structural color colloidal sols of perovskite nanosheets were synthesized and were immobilized in a polymer hydrogel film by in situ photopolymerization, leading to a novel mechanochromic material. Visible absorption spectroscopy, polarized optical microscopy and small-angle X-ray scattering revealed that the nanosheets are aligned parallel to the film surface with the periodic distance of up to ca. 300 nm, giving the structural color tunable over full color range. The present structural color gel showed reversible mechanochromic response that detects weak stress of 1 kPa with the quick response time less than 1 ms as well as high mechanical toughness (compressive breaking stress of up to 3 MPa). These excellent properties are suitable for applications for mechano-sensors and displays., (© 2021 Wiley-VCH GmbH.)