Assessing the influence of nanoscale morphology on the mechanical properties of semiconducting polymers

The ease of processability of conjugated organic polymers, alongside their capability of transporting charges, makes them excellent candidates for applications in flexible and biocompatible electronic devices. In such applications, retaining the electronic properties upon repeated cycles of mechanical strain is key to avoid losing device performance over time. To achieve an accurate mechanical characterization at the nanoscale of these partially crystalline systems, it is critical to have access to reference values of polymer elastic constants and to be able to relate them to the local morphology. With this objective, in the following, we set up a computational protocol for the calculation of elastic constants through molecular dynamics (MD) simulations in the linear deformation regime. We apply such a scheme to the prediction of the elastic behavior of two well-known semiconducting polymers (C16-IDTBT and C14-PBTTT) in crystalline and amorphous phases, showing that the local fluctuations of the Young's modulus can span two orders of magnitude owing to its strong dependence on morphology, anisotropy, and strain direction. The comparison with experimental measurements of the Young's modulus on the nanoscale suggests good agreement in calculated trends.