Effects of interface affinity on the rheological properties of zinc oxide nanoparticle-suspended polymer solutions

The effects of the interface affinity between the nanoparticle and polymer matrix on the rheological properties of nanoparticle suspended-polymer solutions were investigated. Two polymers, polar polyacrylonitrile (PAN) and nonpolar polystyrene (PS), were selected, and the cosolvent was N,N-dimethylacetamide and 0.1∼5 wt% of polar ZnO nanoparticles in the polymer were used. The inclusion of ZnO notably increased the viscosity (η') of the PAN solutions, even at such a low loading level of 0.1 wt%. A maximum value of η' was observed at a 1 wt% of ZnO content. On the other hand, the η' of the PS solutions decreased with increasing ZnO content. Both the PAN and PS suspension systems exhibited a notable decrease in η' above a critical ZnO content. Although the PAN solutions showed a lower loss tangent (tanδ) at higher ZnO contents, the PS solutions containing > 2 wt% ZnO showed higher tan δ above a frequency of 2 rad/s. On the Cole-Cole plot, the PAN solutions did not give a single master curve depending on the ZnO content. However, the PS solutions showed little scattering from the master curve of a slope of ca. 1. ZnO increased the relaxation time of the PAN solutions but decreased the relaxation time of the PS solutions.