Using chemical heterogeneity and selective attractions to manipulate molecular transport in polymer liquids and networks

We employ the Self Consistent Cooperative Hopping theory to systematically investigate the effect of polymer chemical heterogeneity and selective matrix-molecule attractions on the activated dynamics of dilute penetrants. Three distinct systems are studied. (i) Selective AB copolymer melts where a fraction of monomers attracts the penetrant. (ii) A crosslinked homopolymer network where penetrants are attracted to crosslinks. (iii) Associating copolymers where sticky monomers self-assemble into disordered microdomains and a penetrant is attracted to either the crosslinked sticky monomers or the non-sticky monomers. We find that an optimal value of selective monomer fraction results in a large enhancement of molecular size selectivity as compared to athermal or fully attractive homopolymer matrices. The physics involves the interplay of preferential solvation, attractive trap density, and collective elastic effects on penetrant hopping. Increasing molecule-polymer attraction to the clustered monomers results in a sharp dynamic transition from a diffusive to localized state of the penetrant. This behavior is in contrast to when the penetrant is attracted to the non-sticker where vehicular-like transport is predicted at large attraction strengths.