Interfacial adhesion and self-healing kinetics of multi-stimuli responsive colorless polymer bilayers

Simple self-healing behavior of polymers that respond to multiple physicochemical stimuli are highly desirable for industrial applications. In this study, under various external environmental stimulating factors, we focus on the self-healing kinetics of polymer bilayer films (PBFs) comprising a colorless polyimide (CPI) bottom-substrate layer and linseed oil loaded microcapsule (LOMC)-embedded polydimethylsiloxane (PDMS) upper-healing layer. The experimental results showed clear correlation between stimulating factors and the healing time. Although the crack-healing behavior of PBF with 5 wt% microcapsule under air atmosphere is fairly slow, it has an improved healing effect at the artificial crack interface heating to 70 °C; moreover, gradual healing is observed by moisture absorption in environments with relative humidity of 70%. Remarkably, we found that ultraviolet (UV)-light irradiation through the 5 wt% LOMC-filled PDMS layer triggers a noticeable kinematic advantage for the drying reaction that initiates interfacial self-healing. Short-time (20 min) UV-irradiated PBF 5 wt% exhibits a low water vapor permeability of 35.4 g m⁻² day⁻¹ and excellent healability with ~91% recovery by single capsule-type photochemical-induced self-healing. The proposed approach advances the extrinsic healing of colorless polymers in a kinetically effective way without compromising their chemical composition.