Recoverably and destructively deformed domain structures in elongation process of thermoplastic elastomer analyzed by graph theory

Thermoplastic elastomer (TPE) by ABA triblock copolymer chains undergoes microphase separation with bridge and loop chains. TPE has a multi-scale structure containing both bridge chain networks and microphase separated structures in meso scale. In the uniaxial elongation process of TPE, coalescence and breaking of domains occur, and an irreversibly deformed structure forms at high strain. To understand the structural changes in an elongation, we performed coarse-grained molecular dynamics simulations of the elongation process of TPE and analyzed the changes of both the bridge chain network and domain structure by graph theory. Both the changes of the domain structures and recombination of bridge chains can be understood by the descriptors of each graph structure. Using the graph description, two types of structures can be found in the elongation process; recoverably and destructively deformed structures. The graph is one of the most useful mathematical descriptors to understand the topology of bridge chain network inside the structures of TPE in the elongation process, including fracture of domains with a microscopic chain conformation.