Crystallization Behavior of Disproportionately High and Low Molecular Weight PEO Blends

The crystallization behavior of PEOs with molecular weight of 10 k and 200 k as well as their blends was studied in details. The results show that the lower molecular weight PEO crystallizes with faster crystallization rate as judged from a shorter time for completing the crystallization. On the other hand, the higher molecular weight PEO crystallizes at relatively higher temperature, indicating an early start of crystallization compared with the lower molecular weight one. The blends of these two PEOs with different blend ratios always cocrystallize during the cooling processes. It is confirmed that mixing of the 10 k PEO with the 200 k one is in favor of the crystallization of the system. This is not only demonstrated by the early start of the crystallization at higher crystallization temperature, and also a faster crystal growth of the blend with respect to the 200 k PEO. The crystallization of the blends at higher temperature is caused by an early start of nucleation and an increment of nucleus density. This may originate from the density fluctuation of the blend and a reduction in energy barrier for nucleation. Moreover, it is found that the crystallinity of the 10 k PEO rich blends increases with increasing concentration of the 10 k PEO. This is caused by the solvent effect of the 10 k PEO toward the 200 k PEO. On the other hand, the crystallinity of the 30/70(10k/200k) PEO blend is decreased a little bit. This may be a balanced result of the improved crystallization of the 200 k PEO at the expense of the high crystallization ability of the 10 k PEO.