474022 Predicting Mechanical Properties of Organic Semiconductors from Molecular Dynamics Simulations

Thursday, November 17, 2016: 2:45 PM
Continental 3 (Hilton San Francisco Union Square)
Samuel Root, Darren Lipomi and Gaurav Arya, Department of NanoEngineering, University of California San Diego, La Jolla, CA

The mechanical properties of organic semiconductors are of critical importance for roll-to-roll production and thermomechanical reliability of organic electronic devices. Here, we describe the use of coarse-grained molecular dynamics simulations to predict the density, tensile modulus, Poisson ratio, and glass transition temperature for poly(3-hexylthiophene) (P3HT) and its blend with C60. We show that the resolution of the coarse-grained model has a strong effect on the predicted properties. In particular, we find that a three-site model treating each 3-hexylthiophene unit by three coarse-grained beads predicts values of density and tensile modulus that are much closer to experimental measurements than a one-site model. The three-site model also correctly predicts the strain-induced alignment of chains as well as the vitrification of P3HT by C60 and the corresponding increase in the tensile modulus. We also observe a decrease in the radius of gyration and the density of entanglements of the P3HT chains with the addition C60 which may contribute to the experimentally noted brittleness of the composite material. Although extension of the model to poly(3-alkylthiophenes) (P3ATs) containing side chains longer than hexyl groups correctly predicts the experimental trend of decreasing modulus with increasing length of the side chain, obtaining absolute agreement could not be accomplished by a straightforward extension of the three-site model, indicating limited transferability of such models. Nevertheless, the accurate values obtained for P3HT and P3HT:C60 blends suggest that coarse graining is a valuable approach for predicting the thermomechanical properties of organic semiconductors of similar or more complex architectures.

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See more of this Session: Mechanics and Structure in Polymers
See more of this Group/Topical: Materials Engineering and Sciences Division