Growth Rate of Isotactic Polystyrene Crystals in Thin Films

The lateral crystal growth rate of isotactic polystyrene lamellae developing in thin films (ranging from 20 nm to 500 nm) decreases with decreasing film thickness. The decrease in growth rate is inversely proportional to the film thickness: G ( D )= G (∞)(1- d / D ), where G ( D ) is the growth rate in a film of thickness D , G (∞) is the growth rate in the bulk, and d is a constant with a value of approximately 6 nm. Additionally, d is observed to be independent of the crystallization temperature; molecular weight and substrate material used in this study. It is proposed that the constant value of d corresponds to the tube diameter in the reptation model of polymer dynamics, and that near the substrate this diameter is reduced, thereby reducing the mobility of the molecules, and consequently the crystal growth rate.