(561a) Predicting Mixing Free Energy for Polymers with Atomistic Simulations | AIChE

(561a) Predicting Mixing Free Energy for Polymers with Atomistic Simulations

Authors 

Gomez, E. D., The Pennsylvania State University
Milner, S. T., The Pennsylvania State University
The phase behavior of polymer blends depends on the mixing free energy of the constituents. Obtaining the mixing free energy from atomistic simulations is challenging. Our group has previously developed two approaches: 1) atomistic morphing, which requires structurally similar polymers, and 2) mutual ghosting, which can be applied to molecules of any structure, but is involved and computationally expensive. Here, we present a new generally applicable method, in which we apply equal and opposite cosine potentials to the polymers, to induce a concentration variation. Polymers with repulsive interactions will respond to the potential with a larger concentration variation; in this way, we can evaluate the interaction strength between polymers. First we test the new “push-pull” method on bead-spring polymer blends, with results comparable to previous approaches. Then, we investigate a challenging system: blends of P3HT donor polymers and ITDBR acceptor molecules used in organic photovoltaic (OPV) materials. The donor-acceptor interface in such materials plays a key role in exciton binding and dissociation; the interfacial width is governed by the Flory-Huggins chi parameter between donor and acceptor moieties, which we can now predict from simulations.