Buckling-driven Heterogeneous Mechanochemical Response in Thermoplastic Copolymer Elastomers

In recent years, research on force-responsive molecules has grown, providing opportunities to develop mechano-responsive materials for a variety of applications. While there has been progress towards the development of force-responsive molecules (mechanophores) with a variety of response mechanisms, the relationship between the host material's local environments and mechano-activity remains unclear. As a result, the rational development of force-responsive bulk materials using mechanophores faces some challenges. Recent studies have illustrated that microphase-separated triblock copolymers show promise as mechanophore carriers over conventional elastomers, due to the coexistence of hard and soft domains on micro-structural scales. Here, we take steps towards exploring this design space using coarse-grained molecular dynamics simulations of thermoplastic triblock copolymer elastomers functionalized with mechanophores. We have identified two mechanisms by which the coexistence of hard and soft domains produces heterogeneous mechanical loading, especially in lamellar morphologies. These mechanisms are driven by hard domain buckling and soft domain cavitation, producing mechanochemical behavior that depends on the mechanophore's position along the polymer chains. We present results from molecular-scale simulation data, as well as the implications for the community's understanding of force transfer in thermoplastic materials.