Nanocomposite Hydrogels with Optic–Sonic Transparency and Hydroacoustic-Sensitive Conductivity for Potential Antiscouting Sonar

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,N-dimethylacrylamide) 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.