(587e) Particle-Based Simulations of Chiral Block Copolymers Yields Insights into Thermodynamics

Recent advances in polymer synthesis have led to the development of chiral block copolymers, which are capable of exhibiting several interesting phenomena arising from self-assembly. During chirality transfer, the formation of chiral microstructures arises from chiral (helical)conformations produced by chiral building blocks. Several thermodynamic factors play a role in the self-assembly such as the entropy, enthalpy, and fluctuation effects due to the change in conformation. Furthermore, thermodynamic properties such as order-disorder transition temperature appear to depend on the particular chemistry of the chiral block. In this work, we developed a particle-based simulation model to evaluate distinct thermodynamic metrics and to compute the conformational statistics of chiral molecules. Five distinct parameters produce a wide range of helical conformations of varying pitch, resulting in two distinct thermodynamic behaviors. In the first study, the monomers in the two blocks interact with the same potential, differing only by the conformation. By performing free energy calculations, we obtain the entropy change between the helical molecule and random coil and find that it follows a simple theoretical model. The conformational change also drives a change in the enthalpic contacts, producing two distinct regimes that depend on the average pitch of the helix. These two distinct regimes are also observed when chemical incompatibility of the two blocks is introduced. These insights suggest that in chiral block copolymers, details of the conformation matter significantly. Thus, by tuning the intramolecular interactions, the conformations and resulting thermodynamics can be tuned. In the second study, we examine the behavior of chiral block copolymers that are pre-assembled in the lamellar microstructure to investigate the impact of the morphology on the conformations. Surprisingly, we find that the morphological constraints of the microstructure result in a change in the helical nature of the conformations, when compared to an isolated,single chain. This suggests a tradeoff occurs, where enthalpic contacts between unlike monomers are reduced, but that an internal strain occurs in chain conformations.