(698a) Theoretically-Informed Simulations of Block Copolymers

Block copolymers with controlled nanoscale structures are employed in a variety of applications, including as membranes for separations and as chemically and mechanically stable battery electrolytes. We study how polymer architecture and ion content affect these materials’ microphase structure and dynamical properties, using a combination of statistical mechanical theory and molecular dynamics (MD) simulations. Specifically, we implement a freely-jointed-chain model in both fluids density functional theory (fDFT) and in MD simulations; both methods allow us to capture bead-scale packing effects especially relevant near interfaces and in ionic systems. The fDFT results allow us to efficiently determine the equilibrium nanostructure and ensure the MD simulations are initialized in the appropriate microphase separated state. Thus, the simulations equilibrate more quickly than simulations started from a random initial state and we avoid becoming kinetically trapped in metastable structures. Using this approach, we studied the structure and dynamics of tapered block copolymers, which consist of a block of A monomers and a block of B monomers separated by a gradient block (taper) whose composition smoothly changes from A to B (or B to A for an inverse taper). Increasing the length of the taper as a fraction of the total polymer length widens the interfacial region of the microphase structure and lowers the maximum purity of A or B in the middle of the microphase domains. Interestingly, the changes in dynamics versus a typical diblock cannot be predicted via a simple correlation with these structural changes. We also applied our methodology to calculate the diffusion constant of small molecule penetrants that preferentially dissolve in one block of the copolymer and to study the effect of ions on the microphase separation of these systems. We find the theoretically-informed simulation strategy is especially useful for systems with long chains or nonlamellar structures.