Molecular Modeling of Failure in Polymer Nanocomposites

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The availability of light, strong and tough materials is essential for advances in modern engineering and to the technological future of society. Nanocomposite materials consisting of a polymer matrix with distributed nanoparticles are of current interest. These materials can provide significant property improvments relative to the pure polymer. Yet, current continuum mechanics based theories are unable to explain these findings. This award is concerned with fundamental research on the mechanisms that lead to the desireable properties of polymer matrix nanocomposites. The anticipated outcomes of this award will thus allow materials engineers for further advances the science and engineering of nanocomposites and contribute to the general goals of the Materials Genome Initiative. The award also supports associated educational and outreach activities.This award supports research with the goal to uncover how plastic deformation originates, or terminates, near a nanoparticle surface and leads to the formation of shear bands. For amorphous solids it has recently been demonstrated that regions prone to irreversible deformation can be detected from the examination of their internal low frequency vibrational modes. The modes that comprise the so-called boson peak excite the soft regions in the material, or the regions that are most likely to fail under applied load. The present work will begin by characterizing the distribution of these modes around a nanoparticle placed in a model polymer matrix as a function of the particle size and interaction energy with the matrix. Then, a recent computational polymer model exhibiting a ductile-to-brittle transition, the study will investigate how the nanoparticles lead to failure in a pillar geometry. Finally, the goal is to computationally engineer various surface chemistries to enable an ultimately tougher polymer nanocomposite material.