Bionic Boston ivy adhesive foot – photothermal flexible phase change hydrogel

Abstract

Inspired by the adhesion and peeling process of Boston ivy, a novel dual-layer composite photothermal phase change material (cPCM-LIG) is proposed, integrating laser-induced graphene (LIG) as the photothermal conversion layer and a hydrated salt-based phase change hydrogel (cPCM) as the energy storage matrix. The LIG layer, fabricated by laser-induced carbonization of polyimide, exhibits a porous structure and forms strong interfacial adhesion with the cPCM through hydrogen bonding and mechanical interlocking during the crystallization process. The cPCM, synthesized from sodium acetate trihydrate-formamide-polyacrylamide (SAT-FA-PAM), has tunable phase transition temperatures (30–56.3 °C) and high latent heat (126.9–206.3 J g⁻¹). This bilayer design allows the material to efficiently absorb light (95.5%) and convert it to thermal energy (93.5% efficiency) with only 0.2% LIG content while maintaining high energy storage density. The cPCM demonstrates excellent dual-phase flexibility and mechanical performance, with maximum elongation rates of 716% and 1654% in the molten and crystalline states, respectively. In thermal management applications, the composite material can maintain a stable therapeutic temperature (41.5–44.1 °C) for up to 50 minutes after 10 minutes of solar irradiation. This work provides a cost-effective strategy for developing high-performance, flexible photothermal phase change materials with broad applications in solar thermal energy storage and wearable thermotherapy.