Effects of Dynamic Bonds on the Kinetic Pathways of Supramolecular Diblock Copolymers Disorder-Order Transition

Abstract

Supramolecular block copolymers (SBC) consist of covalent polymer building blocks that are connected into well-defined architectures via supramolecular bonds. Assisted by the dynamic and reversible supramolecular interactions, it is envisaged that SBC self-assemblies may exhibit more diverse morphologies, stimuli-responsivity comparing to their covalent analogues. At the fundamental level, these features are related to the free-energy landscape of self-assemblies. It is therefore of central importance to understand the impact of dynamic/reversible bonds on the free energy landscape during structure transitions. In this study, we first conduct smart Monte Carlo simulations to compare the kinetics of the disorder-order transition (DOT) of supramolecular diblock copolymers (SDBC) to that of covalent diblock copolymers (CDBC). The structural order parameter for CDBC exhibits a fast and smooth transition process across different random number seeds and initial configurations. In contrast, the SDBC system shows more diverse transition pathways, which can be classified into three types. These results suggest that reversible supramolecular interactions complicate the pathways, and bring about various intermediate structures. Next, we apply the string method to construct the minimum free energy path of the transition, from which the transition state and the free energy barrier are evaluated. It is found that the transition free energy barrier strongly correlates with the fraction of supramolecules. By decomposing the free energy into A-B interaction energy and association energy, we found that the interplay of both two effects decide the kinetic pathway and the final equilibrium structures.