Molecular Dynamics Simulations of Diffusion of O2and N2Penetrants in Polydimethylsiloxane-Based Nanocomposites

Recently, metal particle polymer composites have been proposed as sensing materials for micro corrosion sensors. To design the sensors, a detailed understanding of diffusion through metal particle polymer composites is necessary. Accordingly, in this work molecular dynam-ics (MD)simulations are used to study the diffusion of O2and N2penetrants in metal particle polymer nanocomposites composed of an uncross-linked olydimethylsiloxane (PDMS)matrix with Cu nanoparticle inclusions. PDMS is modeled using a hybrid interatomic poten-tial with explicit treatment of Si and O atoms along the chain backbone and coarse-grained methyl side groups. In most models examined in this work, MD simulations show that diffu-sion coefficients of O2and N2molecules in PDMS-based nanocomposites are lower than that in pure PDMS. Nanoparticle inclusions act primarily as geometric obstacles for the diffusion of atmospheric penetrants, reducing the available porosity necessary for diffusion, with instances of O2and N2molecule trapping also observed at or near the PDMS/Cu nanopar-ticle interfaces. In models with the smallest gap between Cu nanoparticles, MD simulations show that O2and N2diffusion coefficients are higher than that in pure PDMS at the lowest temperatures studied. This is due to PDMS chain confinement at low temperatures in the presence of the Cu nanoparticles, which induces low-density regions within the PDMS matrix. MD simulations show that the role of temperature on diffusion can be modeled using the Williams-Landel-Ferry equation, with parameters influenced by nanoparticle content and spacing.