Roles of Interfaces in Crystallization in Freestanding and Bilayer Polymer Films

We apply molecular dynamics simulations to quantify the effects of free surfaces and interfacial regions on crystallization in freestanding and bilayer polymer films. We show that enhanced crystal nucleation in polymer thin films is quantitatively correlated to faster local segmental dynamics induced by free surfaces. When a second layer is deposited onto a semicrystalline film, we observe rapid primary nucleation near the free surface, secondary nucleation near the semicrystalline interface, and slower primary nucleation near the center of the fresh polymer layer, which can result in enhanced crystallization in the interlayer region and impact the interfacial strength. We expect molecular insight into thin-film and bilayer polymer crystallization to help optimize polymer products manufactured by layer-by-layer processes.