Photocurable 3D-printed multifunctional phase change hydrogels with reversible soft-hard switching and tunable properties

DLP 3D printing and solvent engineering are combined to fabricate multifunctional PCHs. • SAT crystallization endows PCHs with soft-hard switching and latent heat storage. • Initial NaAc content and immersion pH enable tunable mechanical and thermal performance. • The PCHs exhibit tensile modulus up to 152.29 MPa and adhesion strength on wood up to 540 kPa. • The PCHs enable on-demand adhesion, protection, thermal regulation, and information encryption. Phase change hydrogels (PCHs) have attracted considerable attention for thermal energy storage and personal thermal management because of their high latent heat capacity. However, their practical use remains limited by insufficient structural customizability, interfacial adhesion, mechanical robustness, and durability under complex conditions. Here, we report a multifunctional soft-hard switchable PCH system fabricated through a two-step strategy that decouples hydrogel network construction from the incorporation of sodium acetate trihydrate (SAT) as the phase change component. In this process, 3D-printed hydrogel matrices are immersed in a supersaturated sodium acetate (NaAc) solution to form crystalline SAT layers, yielding a mechanically adaptive architecture with a stiff outer shell and a soft hydrogel interior. By regulating the initial NaAc content in the precursor resin and the pH of the immersion solution, the ionic interactions and crystallization behavior can be modulated, enabling tunable mechanical properties, adhesion, energy absorption, and latent-heat storage. The resulting PCHs exhibit tensile modulus ranging from 0.56 to 152.29 MPa, shear adhesion strengths of up to 540 kPa, and latent heat release of 110.04 J·g⁻¹ . The reversible soft-hard switching enables controllable adhesion, impact and puncture protection, rapid and repeatable heat release, and thermochromic information encryption through exothermic crystallization. This work establishes a two-step generalizable strategy for programmable PCHs and offers an effective route toward multifunctional hydrogels with robust performance under complex environmental conditions. Download: Download high-res image (260KB) Download: Download full-size image