Molecular dynamics simulation of O₂diffusion in polydimethylsiloxane (PDMS) and end-linked PDMS networks

Abstract

Molecular dynamics simulations are used to compute diffusion coefficients for O2 molecules in polydimethylsiloxane (PDMS) and end-linked PDMS networks. The PDMS chains and penetrants are modelled using a hybrid interatomic potential which treats the Si and O atoms along the chain backbone explicitly while coarse-graining the methyl side groups and penetrants. In PDMS models with different molecular weights, diffusivity of the O2 penetrants is found to modestly decrease with an increase in chain length. To match typical experimental conditions, the end-linked PDMS networks are constructed with a PDMS to crosslinking (CL) molecule mass ratio of 5:1 or 10:1, demanding that the number of CL molecules exceeds the number of PDMS chains in each model. Despite end-linking, the presence of non-bonded CL molecules promotes increased O2 diffusivity in comparison with uncrosslinked PDMS. Temperature dependence is captured using the Williams–Landel–Ferry equation.