The sorption induced glass transition in amorphous glassy polymers

Sorption of CO2 in both the glassy and the rubbery state of an amorphous po lyethylenelike polymer was investigated using molecular dynamics simulation s. The temperature was chosen such that the system was in its glassy state at low solute concentrations and its rubbery state at large solute concentr ations. Both the pressure and the volume isotherms changed character at the transition concentration. The physical origin of these changes was clarifi ed by investigation of the excess thermodynamic properties of the solute bo th below and above the transition concentration. Dynamical changes occuring at the glass transition were studied through the self-intermediate scatter ing function of the polymer atoms. This function was found to excellently r eveal the difference between the dynamics of the glassy and rubbery state a nd therefore served as an independent tool monitoring the glass transition. (C) 1999 American Institute of Physics. [S0021-9606(99)50522-9].