Confined Crystallization of Polyethylene Oxide in Nanolayer Assemblies

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Abstract
The design and fabrication of ultrathin polymer layers are of increasing importance because of the rapid development of nanoscience and nanotechnology. Confined, two-dimensional crystallization of polymers presents challenges and opportunities due to the long-chain, covalently bonded nature of the macromolecule. Using an innovative layer-multiplying coextrusion process to obtain assemblies with thousands of polymer nanolayers, we discovered a morphology that emerges as confined polyethylene oxide (PEO) layers are made progressively thinner. When the thickness is confined to 20 nanometers, the PEO crystallizes as single, high-aspect-ratio lamellae that resemble single crystals. Unexpectedly, the crystallization habit imparts two orders of magnitude reduction in the gas permeability.