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College Park, Maryland      June 6 - 10 , 2004

WP22: Structure of polymer-nanocomposites A SANS and USAXS study

R. A. Narayanan, P. Thiyagarajan (Intense Pulsed Neutron Source, Argonne National Lab), B.J. Ash, S.S. Sternstein, A.J. Zhu, L. Schadler (Materials Science and Engineering Department, Rensselaer Polytechnic Institute, Troy, NY- 12180)

Alumina/ polymethylmethacrylate (PMMA) nanocomposites synthesized by an in situ free-radical polymerization in the presence of 38 nm alumina nanoparticles exhibit unusual brittle-to-ductile transition with a large increase in the strain-to-failure. In order to understand the molecular mechanisms responsible for the reinforcement of polymeric materials by nano-sized inorganic fillers, we have undertaken small-angle neutron (SANS) and ultra small angle x-ray scattering (USAXS) measurements on alumina-PMMA and silica-PVAc nanocomposites, in combination with studies on their mechanical behavior. SANS studies of alumina-PMMA composites show a large degree of aggregation and agglomeration of alumina that depends on the size of the nanoparticles. Moreover, composites containing 5 and 10 wt.% deuterated PMMA indicate that addition of nanoparticles does not seem to affect the Rg of the polymer (PMMA). These results have to be investigated further by contrast matching the scattering from the alumina using appropriate mixture of deuterated and normal PMMA. USAXS data on silica-PVAc nanocomposites a large degree of aggregation of silica is observed. The particles show an average aggregation of about 250 which is significantly reduced in the case of surface treated fillers. Evidence suggests that the surface fractal dimension, which is a measure of surface roughness, is directly related to reinforcement characteristics of the composite.

This work benefited from a grant from Office of Naval Research to LS at RPI, and IPNS and APS facilities funded by DOE under contract no. W-31-109-ENG-38 to the University of Chicago. UNICAT facility is supported by the DOE, the State of Illinois-IBHE-HECA, NSF, NIST (U.S. DOC) and UOP LLC.

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