Molecular simulation and experimental studies of the miscibility of polylactic acid/polyethylene glycol blends

Computer simulation and experiments were performed to investigate the miscibility of PLA/PEG blends with different PEG concentrations. Flory-Huggins interaction (chi) parameter used to predict the miscibility for the blends was estimated by molecular dynamic simulation of fully atomistic model. The calculated. parameter and radial distribution function suggest that the PLA and PEG blends are likely miscible at low PEG concentrations (10-30 wt%), but they become apparently immiscible at higher PEG content (> 50 wt%). This result is consistent with density distribution of PLA and PEG beads calculated from dissipative particle dynamics simulation of coarse-grained model. To support the computational results, experiments based on differential scanning calorimetry (DSC) and rheometry were also performed. The DSC thermograms of 90: 10, 80: 20, and 70: 30 (wt/wt) of PLA/PEG blends showed a single glass transition and PLA melting peak, indicating PLA/PEG is miscible over this composition. In rheometry, frequency (omega) dependence of storage moduli (G') at low frequencies for 75: 25 and 70: 30 blends indicate that these samples are near the phase separation point.