High Temperature Stability of Dewetting-Induced Thin Polyethylene Filaments

We investigated the stability and crystallization behavior of a polygon-network of thin filaments of ultrahigh molecular weight polyethylene, generated by dewetting of a spin-coated film of hot p-xylene solution on a solid substrate. Due to the shear forces occurring in the course of dewetting, the PE-chains in the filaments were expected to be highly stretched, corroborated by their partial decoration with edge-on lamellar crystals resulting in so-called shish-kebab structures. Above an annealing temperature of 134 °C, the filaments exhibited a liquid-like behavior and were thus prone to decay to droplets according to the Plateau-Rayleigh instability. Intriguingly, even after prolonged annealing at temperatures up to almost 100 degrees above the melting temperature of polyethylene for times significantly longer than the corresponding bulk reptation time, semi-cylindrical PE filaments as small as 50 nm did not decay into droplets. Furthermore, after such prolonged annealing and subsequent quenching to room temperature, these filaments were still capable of inducing shish-kebab structures. We tentatively conclude that polymer chains confined in nanoscopic filaments kept some memory of the dewetting induced stretching and can undergo only slower conformational changes and rearrangement processes than observed in an equilibrated melt.