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Non-Linear Deformation of Tethered Sio2 Nanocomposites

Vivek Goel1, Joanna Pietrasik2, Krzysztof Matyjaszewski2, and Ramanan Krishnamoorti1. (1) Chemical Engineering, University of Houston, 4800 Calhoun, Houston, TX 77204 - 4004, (2) Chemistry, Carnegie Mellon University, 4400 Fifth Avenue, Pittsburgh, PA 15213

Brush-like nanocomposites with the polymer chains end-grafted to hard inorganic cores are very useful in probing structure-property relations with applications from colloid stabilization to polymer compatibilization, with the brush geometry a net result of competing entropic factors. Application of inorganic nanocomposites as fillers in organic polymer matrices requires good dispersion of the filler particles, in order to maximize surface area and stress transfer through interaction of the constituent domains.

In this talk, we focus on highly curved surfaces of inorganic SiO2 filler particles, with poly(butyl acrylate) chains end-grafted through the living polymerization process of ATRP. While linear rheological examination supports a solid-like response of the filled system at less than 4 vol% of the filler loading, small angle X-ray scattering (SAXS) reveals a well-defined local ordering of the domains, supported by electron microscopy. Local chain dynamics was also significantly slowed down due to presence of the compatible SiO2 surface. Dilution of the hybrid nanocomposites with homopolymer chains resulted in a scaling of the plateau modulus and domain spacing, consistent with previous observations from block copolymers. Non-linear deformation via application of shear probed the defect-mediated ordered mesoscale structure rupture and quiescent state relaxation of the structure upon cessation of shear for various time scales, and will be discussed in context of dispersion state of domains through rheological measurements. In-situ SAXS, used for probing structure rupture and reformation, will also be discussed in conjunction with rheological investigations.