In this paper, we report on the design and simple fabrication of novel nanocomposite hydrogels with optic−sonic transparency and hydroacoustic-sensitive conductivity. The proposed nanocomposite hydrogels are constructed by poly(N,Ndimethylacrylamide) and exfoliated Laponite clay nanosheets via free radical polymerization. With lithium chloride (LiCl) as ionic additives inside the polymeric networks of the hydrogels, the lithium cations (Li + ) could be stored on and in the clay nanosheets owing to the electrostatic adsorption and cation exchange. Triggered by hydroacoustic wave oscillation, the stored Li + ions could escape from the clay nanosheets, resulting in the augmentation of ionic concentration inside the polymeric networks and thus the increase of the conductivity of the nanocomposite hydrogel. Inversely, upon removing the hydroacoustic signals, the Li + ions could be readsorbed again by the clay nanosheets; as a result, the conductivity of the nanocomposite hydrogel decreases again. Moreover, the fabricated nanocomposite hydrogels also feature high stretchability and spliceable and antifreezing properties. Such novel nanocomposite hydrogels are highly promising for development of systems for camouflaging and sensing sonar scanning.

In this study, novel humidity-responsive actuators are developed based on firm heterojunction of glycerol-cross-linked polyvinyl alcohol (Gly@PVA) and porous polyvinylidene fluoride (PVDF) via a facile strategy for achieving humidity control and anti-condensation functions. The firm heterojunction of Gly@PVA and PVDF with extremely high interfacial toughness is achieved by simply bonding the Gly@PVA layer and plasma-treated porous PVDF layer via a coating–freezing–drying process. The addition of glycerol in polyvinyl alcohol (PVA) increases the moisture adsorption capacity, resulting in a significant mismatch between the humidity-responsive properties of the humidity-active Gly@PVA and inert PVDF layers. With the mass ratio of glycerol to PVA as 17.5%, the Gly@PVA/PVDF bilayer actuators exhibit humidity-responsive bending behaviors with a bending angle change as large as 216.4° when the environmental relative humidity (RH) changes from 25 to 95%. Based on the humidity-responsive bending property, Gly@PVA/PVDF bilayer films are designed and patterned as humidity-responsive smart gates. By equipping sealed chambers and food crispers with such smart gates, which can rapidly open and release excessive moisture out in time when the inside RH exceeds a critical value, excellent performances of humidity control, anti-condensation, and food preservation are effectively achieved. The proposed strategy is highly promising for developing efficient humidity-responsive actuators for various applications.

Moisture-responsive actuators with biocompatibility, fast response, and tough interfacial bonding are developed as smart breather valves for humidity management. The proposed actuators are featured with a bilayer structure consisting of a moisture-sensitive methacrylated hyaluronic acid (HAMA) layer and a moisture-inert porous poly(vinylidene fluoride) (PVDF) layer. The HAMA/PVDF bilayer films are fabricated by casting HAMA precursor solutions on the ethanol-treated porous PVDF films first and then converting the precursor solutions into crosslinked HAMA hydrogels via UV-initiated crosslinking. The fabricated HAMA/PVDF bilayer films exhibit rapid, reversible, and repeatable moisture-responsive bending performances upon the change of environmental relative humidity. The molecular weight and mass concentration of HAMA in a precursor solution affect the moisture-responsive actuating speed of the HAMA/PVDF bilayer films, and the fastest response time needed for completing 70% of the moisture-responsive deformation of a HAMA/PVDF bilayer film can be as short as 0.5 s. Due to the fast moisture-responsive bending property and biocompatibility, the HAMA/PVDF bilayer films are successfully developed into smart breather valves by designing and patterning them into fence-like structures and then equipped on the outdoor masks for efficient management of humidity inside the masks. The proposed moisture-responsive actuators show great potential in various applications, especially those related to environmental humidity management.

No abstract