Elastic Forces and Molecular Transport through Polymer Matrices

Molecular transport through polymers is the key for many technologies, yet understanding of mechanisms controlling this transport remains limited. We present a survey of many important aspects of molecular transport in polymeric materials and demonstrate that they can be described reasonably well using the Anderson and Stuart model originally introduced to describe the dynamics of ions in glasses. Within this presently adopted approach the activation energy of molecular diffusivities, Emol is largely controlled by the instantaneous elastic modulus of the matrix in addition to its available free volume. As demonstrated for a large number of penetrants, this model is able to explain on both qualitative and quantitative levels many of the previously reported correlations between Emol and molecular sizes. Based on the outcome of the present analyses, a new recipe is provided for tuning the molecular selectivity of polymeric membranes.