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siloxane_irradiation.pdf (14.24 MB)

A Quantum-Based Approach to Predict Primary Radiation Damage in Polymeric Networks

preprint
submitted on 17.09.2020 and posted on 18.09.2020 by Matthew Kroonblawd, Nir Goldman, Amitesh Maiti, James Lewicki
Initial atomistic-level radiation damage in chemically reactive materials is thought to induce reaction cascades that can result in undesirable degradation of macroscale properties. Ensembles of quantum-based molecular dynamics (QMD) simulations can accurately predict these cascades, but extracting chemical insights from the many underlying trajectories is a labor-intensive process that can require substantial a priori intuition. We develop here a general and automated graph-based approach to extract all chemically distinct structures sampled in QMD simulations and apply our approach to predict primary radiation damage of polydimethylsiloxane (PDMS), the main constituent of silicones. A post-processing protocol is developed to identify underlying polymer backbone structures as connected components in QMD trajectories. These backbones form a repository of radiation-damaged structures. A scheme for extracting and updating a library of isomorphically distinct structures is proposed to identify the spanning set and aid chemical interpretation of the repository. The analyses are applied to ensembles of cascade QMD simulations in which the four element types in PDMS are selectively excited in primary knock-on atom events. Our approach reveals a much higher degree of combinatorial complexity in this system than was inferred through radiolysis experiments. Probabilities are extracted for radiation-induced network changes including formation of branch points, carbon linkages, cycles, bond scissions, and carbon uptake into the Si-O siloxane backbone network. The general analysis framework presented here is readily extendable to modeling chemical degradation of other polymers and molecular materials and provides a basis for future quantum-informed multiscale modeling of radiation damage.

History

Email Address of Submitting Author

kroonblawd1@llnl.gov

Institution

Lawrence Livermore National Laboratory

Country

United States

ORCID For Submitting Author

0000-0002-5009-5998

Declaration of Conflict of Interest

No conflict of interest.

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