Effect of Melt Molecular Weight and Temperature On the Rheology of Dewetted Polymer-Grafted Nanoparticles in Polymer Melts

The effects of melt molecular weight and temperature on the rheology of polymer-grafted nanoparticles have been investigated in chemically-identical homopolymer melts. The suspensions were formulated such that de-wetting took place between the graft polymer and the melt polymer. Dewetting at the graft polymer/melt polymer interface, controlled by the molecular weights of the graft and melt polymer, N and P, respectively, lead to particle attractions, which lead to a thixotropic rheological response and viscosity-stress curves that can be scaled by temperature and swelling ratio (P/N). The onset of elasticity is denoted by the storage modulus (G') overtaking the loss modus (G”), which occurs at a particle core volume fraction of φ = 0.15, which is essentially independent of the swelling ratio for particles of core radius R = 100 nm. The strength of attraction was modeled using a square well potential based on the swelling ratio, where the interaction potential was used to scale the rheological data. The implications of the power-law dependence of the storage modulus on particle volume fraction are discussed.