Correlating polymer crystals via self-induced nucleation

Crystallizable polymers often form multiple stacks of uniquely oriented lamellae, which have good registry despite being separated by amorphous fold surfaces. These correlations require multiple synchronized, yet unidentied, nucleation events. Here, we demonstrate that, in thin films of isotactic polystyrene, the probability of generating correlated lamellae is controlled by the branched morphology of a single primary lamella. The nucleation density n_s of secondary lamellae is found to be dependent on the width w of the branches of the primary lamella such that n_s ~ w^-2. This relation is independent of molecular weight, crystallization temperature and lm thickness. We propose a nucleation mechanism based on insertion of polymers into a branched primary lamellar crystal.