Size-dependence and interfacial segregation in nanofilms and nanodroplets of homologous polymer blends.

The size-dependent behavior of nanofilms and nanodroplets of homologous polymer blends was explored by many-body dissipative particle dynamics. Although a homologous blend can be regarded as a completely miscible and athermal system, enrichment of the surface in short polymers always takes place. First, liquid-gas and solid-liquid interfacial tensions of polymer melts were acquired. It is found that they increase and approach asymptotes with increasing chain lengths. The molecular weight dependence can be depicted using two semi-empirical expressions. Second, the variation of surface tension and surface excess of polymer blend nanofilms with the thickness was observed. Surface tension of the blend is observed to increase but the extent of surface segregation decreases upon increasing the film thickness. Finally, the wetting phenomenon of nanodroplets of homologous blends was examined. The contact angle is found to increase as the droplet size is reduced. Our simulation results indicate that the size-dependence of nanofilms and nanodroplets is closely related to surface segregation in homologous blends.