Spatiotemporal Sequence of Interdependent Nucleation Mechanisms in Ultrathin Polymer Films

Employing defined starting conditions of ultrathin molten poly(ethylene oxide) films on model solid substrates, we investigated the spatiotemporal sequence of interdependent mechanisms of crystal nucleation. Due to the limited number and the preferred conformation of polymer chains parallel to the substrate, primary nucleation favored edge-on lamellar crystals, which indirectly induced other subsequent nucleation pathways, enabled through the molten polymer chains accumulated at their peripheral fold surfaces. Both additional edge-on lamellar crystals and branched flat-on lamellar crystals were initiated. For long-chain polymers, spatial correlations between lamellar crystals across intervening noncrystalline regions were established through polymer chains incorporated within neighboring lamellae. Triggered by the first-formed crystals, such connecting polymers induced the formation of large arrays of multiple, narrowly spaced, and uniquely oriented lamellar crystals. Preformed ordered polymer structures like nanofilaments in the spin-coated samples allowed one to circumvent the stage of primary nucleation. The interplay and competition of complementary nucleation mechanisms in confined polymer systems led to a complex, large-scale morphology composed of various chronologically formed nanoscale patterns.