Tunability of the dispersion and rheology in PNCs by non-linear polymers at the polymer-NP interface

Attractive interactions between polymer chains and NPs form a bound layer in the PNCs. Previous studies on grafted and linear adsorbed chains on the NPs show that the bound layer has significant impact on dispersion of NPs and rheology of the PNCs. In this study, we used poly(ethylene oxide) with varying architectures (linear, stars and hyper-branched) to explore the effects of modified surfaces by ‘non-linear’ polymers on dispersion state of NPs and bulk rheology of the PNCs. We observed agglomeration in composites with unentangled non-linear polymers at the interface due to the decoupling of NPs and the linear matrix, while individual dispersion is a norm for PNCs with entangled adsorbed polymers. Rheology results in the linear viscoelastic region shows the tunability of the mechanical reinforcement in PNCs by modifying the bound layer through varying functionality, arm lengths, and the number of end group hydrogen bonds in non-linear polymers. In addition, large amplitude oscillatory shear tests show a strong relation between the extend of the linear viscoelastic region and the compactness of the adsorbed polymers. Overall, this study shows that the architecture of the bound polymers can be a powerful new parameter for controlling the rheological properties of the PNCs.