Leaf-Inspired Self-Healing Polymers

Abstract

The Bigger PictureDevelopments of self-healing polymers are primarily driven by the desire to prolong materials' lifetime while maintaining their functions. Significant synthetic efforts have been made over the last two decades via the incorporation of dynamic bonds capable of reversible breaking and reforming. However, the role of physical network design in achieving self-healing properties in commodity polymers remains unclear.Inspired by the self-healing behavior of leaves, we built self-healing into polycaprolactone-polyurethane fibers by controlling morphological features. Favorable viscoelastic properties originating from interphase features facilitate shape memory effects and lead to autonomous damage closure and subsequent self-healing. The creation of morphology-controlled dynamic polymers can be utilized in numerous applications ranging from soft robotics to molecular actuators or morphology-induced information storage to thermomechanical sensing and other devices.Highlights•Inspired by plants leaves, self-healing fibers are developed•Self-healing occurs as a result of favorable interphase morphologies•Molecular events leading to self-healing are examined by spectroscopic analysis•Correlations between morphology, shape memory, and self-healing are establishedSummaryHierarchical multiphase fibrous morphologies provide strength and elasticity for biological species, facilitating responses to environmental changes. Wound closure of leaves is one example. If polymers can be formed in a similar manner by introducing multiphase-separated morphologies, self-healing in a variety of commodity materials can be achieved. In these studies, we demonstrate the role of phase morphologies, interphases, and viscoelasticity-driven shape memory effects on self-healing. We synthesized phase-separated polycaprolactone-polyurethane fibrous thermoplastic polymers in which microphase separation facilitates the formation of stable interfacial regions between hard and soft segments. Self-healing can be repeated many times. This behavior is attributed to the shape memory effect, given that micron-scale interphase reduces chain slippage, enabling entropic energy storage during damage. Chemically identical but nanophase-separated copolymers do not exhibit this behavior. These studies show that self-healing can be achieved by morphology control and facilitated by thermal or other volume-induced transitions.Graphical abstract