High Energy Density, Mechanical Robustness, and Solvent Resistance Supramolecular Solid−Solid Phase Change Materials for Photothermal Actuation

Abstract

Solid−solid phase-change materials (SSPCMs) possess enormous application potential in advanced thermal management. Nevertheless, they have long been plagued by a trade-off between mechanical strength and high energy density, accompanied by drawbacks such as poor solvent resistance and insufficient shape-memory capacity. Herein, the above challenges are addressed via a molecular engineering strategy. For the first time, sp2-hybridized boron atoms are utilized to strengthen hydrogen-bonding interactions for constructing reversible physical cross-linking networks of solid−solid phase change materials. Within this system, polyethylene glycol (PEG) serves as the thermal storage unit, while boron-mediated hydrogen bonds act as physical cross-linking sites. The as-fabricated SSPCMs simultaneously achieve an ultrahigh energy density of 120.1 J g−1 and an excellent mechanical strength of 38.3 MPa. The densely packed physical cross-linking network endows the material with outstanding stability and solvent resistance. Even with an extremely high loading of PEG phase-change filler (97 wt %), the material remains solid-state at 150 °C. In addition, it retains its solid morphology after being immersed in various polar and nonpolar solvents for 24 h, which greatly improves its service stability. More importantly, flower-shaped SSPCM actuators exhibit reversible blooming behavior under light or thermal stimulation, offering a new route to realize photothermal/thermally triggered shape memory. In summary, this work offers a molecular-level design strategy for SSPCMs that reconciles high energy density and mechanical robustness while overcoming the persistent limitations of poor solvent resistance and weak shape-memory performance.