Controlling Polymer Crystallization Kinetics by Sample History

摘要

In this paper systematic changes in the isothermal crystallization kinetics (at T_c = 200 °C) of nonequilibrated isotactic polystyrene films, generated through spin coating are reported. Kinetics is tuned by annealing films at T_a = 250 °C, i.e., above their nominal melting temperature (T_m~(DSC) = 220 °C). An exponential decrease in growth rate and a significant decrease of crystal nucleation density by approximately three orders of magnitude are observed by increasing the time (t_a) provided for equilibration at T_a. The characteristic exponential decay time is approximately four orders of magnitude longer than the equilibrium reptation time at T_a. Interestingly, with increasing ta, a change in the morphology of lamellar crystals varying from spherulites to hexagons of rather uniform height to finally hexagons exhibiting periodic modulations in height is observed. These observations reveal that understanding and tuning the crystallization kinetics of polymer films under quiescent conditions requires knowledge on how strongly chain conformations deviate from equilibrium.