Temperature‐Responsive Wettability‐Switching Cross‐Linked Poly(ε‐Caprolactone) Films With Tunable Melting Transitions

ABSTRACT Frost accumulation on air‐side heat exchangers significantly reduces heat transfer efficiency and increases energy consumption, creating a strong demand for effective and energy‐efficient defrosting technologies. Temperature‐responsive wettability‐switching surfaces have attracted considerable attention as promising strategies for anti‐frosting and defrosting applications. In this study, a cross‐linked poly(ε‐caprolactone) (PCL) film is introduced onto a roughened aluminum substrate to construct a wettability‐switching surface. Cross‐linked PCL films are prepared by combining linear PCL (L‐PCL) and branched PCL (B‐PCL) macromonomers at various molar ratios. The optimal composition (L‐PCL/B‐PCL = 30/70) exhibits a melting temperature (Tm) of 35.5°C, which is significantly lower than that of conventional PCL systems (~60°C). The resulting surface shows reversible wettability switching, transitioning from a hydrophobic state (contact angle ≈ 107°) at 30°C to a hydrophilic state (contact angle ≈ 50°) at 40°C, corresponding to a 57° decrease in contact angle within the 30°C–40°C range. This behavior originated from the crystalline‐to‐amorphous phase transition of PCL, while the roughened surface amplified the wettability contrast. The switching behavior remained stable during repeated heating–cooling cycles, demonstrating excellent reversibility. These results highlight the potential of this platform for temperature‐responsive anti‐frosting and defrosting applications in heat exchanger systems.