Polymer epitaxy under heterogeneous confinement

It is challenging to grow polymer crystals which are aligned over long length scales due to the inherent tendency of polymer lamellae to undergo spherulitic branching and splaying during growth. One approach to the creation of ordered and aligned polymer structures is by epitaxial crystallization. Typically, crystallization proceeds in a film of uniform thickness, in which polymer crystals nucleate and grow along rotationally symmetric, epitaxially matched crystallographic directions. In this work, we heterogeneously confine the film into spatially disparate regions of varying thickness to separate the nucleation and growth processes, allowing oriented arrays of epitaxial crystals to grow unimpeded over long distances. We uncover the hierarchical structure of polymers crystallized under heterogeneous confinement and elucidate the undercooling and molecular weight dependencies of pattern formation with experiments and phase-field simulations.