Controlling the Growth of Stacks of Correlated Lamellar Crystals of a Block Copolymer

In the crystallization of polymers, besides mono-lamellar polymer crystals, stacks of correlated lamellae with a unique orientation and signatures of single crystals have often been observed. However, we still lack a generic criterion for such stacking, i.e., vertical growth of polymer crystals. Here, by employing self-induced nucleation on the fold surface of a basal lamella for generating appropriate seeds, we identify experimental conditions allowing for a controlled formation of stacks of crystalline lamellae of a block copolymer. Adopting a two-step crystallization procedure, we decoupled nucleation and growth conditions and thereby favored vertical growth of polymer crystals in thin films. A sufficient reservoir of molten polymers in combination with slow lateral growth of the basal lamella is required for observing the formation of stacks of correlated lamellae. Taking this path, we were able to form stacks reaching heights of about ten times the initial film thickness.