Effects of CO₂ sorption on the rotational reorientation dynamics of a model solute dissolved in molten poly(dimethylsiloxane)

We report on the effects of polymer molecular weight, temperature, and near- and supercritical CO₂ gas sorption on the rotational reorientation dynamics of a model solute (BTBP) dissolved in molten poly(dimethylsiloxane) (PDMS). In order to determine the BTBP rotational dynamics, we have carried out time-resolved fluorescence anisotropy measurements in PDMS polymers of varying molecular weight. These results show that there is a linear correlation between the BTBP rotational reorientation dynamics and the PDMS polymer bulk density. Temperature-dependent studies of the BTBP/PDMS system shows that the BTBP rotational reorientation dynamics are accurately described by an Arrhenius activation model. The recovered activation energies for the BTBP dynamics are statistically the same as the activation energy for PDMS viscous flow. The addition of CO₂ to the BTBP/PDMS system leads to an appreciable decrease in the BTBP rotational reorientation time with CC₂ pressure. These results illustrate how polymer dilation by CC₂ can be used to tailor the dynamics within polymer systems.