Mechanism for the formation of millimeter-long solid filaments by spin coating dilute solutions of a crystallizable polymer

We have investigated the formation of millimeter-long filaments induced by spin-coating ca. 130 °C dilute para-xylene solutions of rapidly crystallizable polyethylene chains with a contour length in the micrometer range onto ca. 80 °C mica substrates. These filaments were radially oriented and accumulated on the periphery of the substrate. Our observations can be explained by the stretching of polymers through the flow field induced by spinning the solution on a solid substrate. The corresponding loss in conformational entropy emphasized attractive interactions between polymers, which resulted in the formation of bundles and their assembly into long filaments. Caused by a Plateau–Rayleigh-type instability of a liquid coating on a solid filament and due to crystallization, these filaments were decorated with various small-scale structures. Still in solution, the resulting filaments experienced a Coriolis force as they were dragged toward the periphery of the sample, causing a deviation of their orientation from the radial direction. Finally, filaments adsorbed on the substrate, solvent evaporated completely, and the resulting variety of crystalline patterns and morphologies were examined by various microscopy techniques.