Effect of confinement on glass dynamics and free volume in immiscible polystyrene/high-density polyethylene blends

The free volume radius of PS/HDPE blend decreased upon annealing, which verified the confinement effect of constriction during crystallization process in the incompatible amorphous/semi‐crystalline blend. The effect of confinement on glass dynamics combined with the corresponding free volume changes of amorphous polystyrene (PS) in blends with semi‐crystalline high‐density polyethylene (HDPE) have been investigated using thermal analyses and positron annihilation lifetime spectroscopy (PALS). Two different glass transition temperatures (Tg) were observed in a PS/HDPE blend due to the dissimilarity in the chemical structure, consistent with an immiscible blend. However, Tg of PS in the incompatible PS/HDPE blend showed an upward trend with increasing PS content resulting from the confinement effect, while Tg of the semi‐crystalline HDPE component became lower than that of neat HDPE. Moreover, the elevation of Tg of PS was enhanced with a decrease of free volume radius by comparing annealed and unannealed PS/HDPE blends. Positron results showed that the free volume radius clearly decreased with annealing for all compositions, although the free volume hole size agreed well with linear additivity, indicating that there was only a weak interaction between the two components. Combining PALS with thermal analysis results, the confinement effect on the glass dynamics and free volume of PS phase in PS/HDPE blends could be attributed to the shrinkage of HDPE during crystallization when HDPE acted as the continuous phase. © 2015 Society of Chemical Industry