of 21 Soft Matter S of tM at te r A cc ep te d M an us cr ip t

Mechanical properties of polymer nanocomposites are significantly affected by spatial ordering of nanoparticles (NPs) which can be modified under shear flow fields. Polymer-grafted iron oxide NPs form strings, well-dispersed, and percolated anisotropic nanostructures depending on grafting density, and herein their mechanical properties under large oscillatory shear flows are reported. We show that flow-induced alignment of NPs is achieved with string-like structures at low particle loadings (5 wt%). Further, entropic surface tension between grafted and free chains decreases by facilitating the penetration of long matrix chains into the grafts with oscillatory shear flow. Consequently, degree of entanglements under large strain amplitudes is enhanced which is reflected in elastic properties. These results indicate that matrix polymer plays an effective role in the reinforcement of polymer-grafted NPs under large shear flow fields.