Regime transition temperature of poly(ethylene oxide) in thin films: Effect of film thickness and molecular weight

In thin films of poly(ethylene oxide), the regime transition temperature between regimes II and III, TIII→II, was found to increase with decrease in the film thickness D below 1 μm and increase in the molecular weight (Mw). When D was 1 μm or greater, TIII→II was found to be highly dependent on Mw and independent of D. As D decreased, the dependence of TIII→II on Mw decreased. The spherulitic growth rate, on the other hand, was almost independent of D for D ≥ 100 nm. These results were discussed based on the suppression of chain mobility in the cases of small D and high Mw. The reduced mobility slowed down the lateral growth rate of secondary nuclei and relatively enhanced the secondary nucleation frequency. The results also implied that the surface free energy of the folded surface decreases with lowering D and that the chain folds are disordered.