Origin of Oriented Recrystallization of Carbon-Coated Preoriented Ultrathin Polymer Films

The origin of oriented recrystallization behavior of vacuum carbon evaporated preoriented polymer thin films was studied by means of transmission electron microscopy and electron diffraction with elaborately designed experimental setups. Through the recrystallization of HDPE in the iPP/HDPE-C sandwich layers with its original chain orientation being preserved by the coated carbon other than epitaxially crystallized on the highly oriented iPP substrate as usually happened without carbon coating, the graphoepitaxial crystallization of the polymer melts on their surface carbon replicas is ruled out of the origin of the oriented recrystallization. Through the different melt recrystallization behavior of melt-drawn 1-iPB thin films on and with vacuum evaporated carbon layers, the strong fixing effect of vacuum evaporated carbon layers on the polymer films has been recognized. This is further confirmed by the dissolution test of the vacuum carbon deposited HDPE thin films. The exact mechanism of the fixing effect of vacuum evaporated carbon layers on the thin polymer films is not quite clear yet. The recognition of the fixing effect is, however, sufficient to explain the oriented recrystallization phenomenon of the carbon coated preoriented thin polymer films. Namely, the vacuum evaporated carbon layer on the polymer thin film has prevented the surface extended macromolecular stems of the crystals from melting or at least from a complete relaxing during high-temperature annealing, and the surface fixing confined crystallization has induced the oriented recrystallization of the thin polymer molten layer.