Structure-property relationships of nanocomposite-like polymer blends with ultrahigh viscosity ratios

We have investigated the structure-property relationships and the effects of a viscosity ratio on the rheological properties of nanocomposite-like polymer blends using oscillatory and steady shear rheometry and optical microscopy. These immiscible blends are consisted of ultrahigh viscous polybutadiene (PB1), high viscous polybutadien (PB2), and low viscous polydimethylsiloxane (PDMS). The PB1/PDMS blends with an ultrahigh viscosity ratio (λ=162,000) exhibit non-Newtonian fluids behavior for Ω≥0.1 while the PDMS/PB2 blends (λ=37) exhibit pseudo-Newtonian fluids behavior for Ω>0.6, where Ω is the weight fraction of PB1 or PB2 in the blends. The viscoelastic properties of the PB1/PDMS blends increase systematically with an increasing the weight fraction of PB1, and then exhibit plateau values above a certain maximum weight fraction (Ωm) of PB1. In addition the viscoelastic properties of the PB1/PDMS blends are not affected by the change of blend morphology or phase inversion, where Ωm is larger than the phase inversion weight fraction (Ωp). In contrast the viscoelastic properties of the PB2/PDMS blends follow a positive-deviation mixing rule and are significantly affected by phase inversion.