(606f) Molecular Dynamics Simulations Predict That Semiconducting Polymers Behave As Ribbons

Modern, high performance semiconducting polymers contain planar heterocyclic residues along their backbone that endow them with the shape of a ribbon: that is, having three spatial dimensions that are widely separated in scale. Yet, the effect of this ribbon-like shape on the statistical mechanics and thermophysical behavior of these polymers is not well understood. Here, using the amorphous semiconducting polymer, PTB7, as a model system, large scale (N ~ 1M) atomistic molecular dynamics simulations are employed to explore the emergent behavior of polymeric ribbons in the solvated, melt, and glassy phases. A focus is placed on the ways in which the chain conformations, packing structure, and response to mechanical deformation of ribbon-like polymers differ from rod-like polymers (i.e. the worm-like chain model). Specifically, we find that molecular ribbons exhibit an oscillatory exponential decay in their tangent correlation functions, as opposed to the non-oscillatory exponential decay found in rod-like polymers. Moreover, predictions of the tensile response of these materials are made, and effects due to molecular weight, polydispersity, and entropic elasticity are explored. Taken together, our simulations suggest ways in which molecular design can be used to co-optimize the mechanical and electronic behavior of semiconducting polymers for applications in soft electronics and robotics. Moreover, the theoretical predictions provide inspiration for the design of experiments to further explore the statistical mechanics of molecular ribbons.