Surface dynamics of glassy polymers with different molecular weight distributions

The surface dynamics of polymers are of great interest in the field of polymer physics. It is generally believed that a 'liquid-like' layer exists at the glassy polymer surface, exhibiting enhanced segmental dynamics compared to the bulk. While much effort has been dedicated to elucidating the underlying mechanism of this simple yet fascinating phenomenon, most studies have focused on polymers with a single molecular weight or a narrow molecular weight distribution. In practical applications, polymeric products consist of a broad range of molecular weights. Consequently, composition of polymers may not be expected to be uniform in space, especially in the presence of an interface. In this study, we investigate the surface dynamics of glassy polymers with a bimodal molecular weight distribution using a droplet wetting-dewetting experiment. The results reveal that the surface dynamics of polymer blends are predominantly influenced by a layer of segregated short-chain polymers. However, upon the removal of this segregated layer, the liquid-like layer begins to dictate the surface behaviors.