4.6 Article

Relaxation dynamics of deformed polymer nanocomposites as revealed by small-angle scattering and rheology

Journal

SOFT MATTER
Volume 18, Issue 46, Pages 8867-8884

Publisher

ROYAL SOC CHEMISTRY
DOI: 10.1039/d2sm00775d

Keywords

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Funding

  1. Oak Ridge Associated Universities
  2. U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Early Career Research Program Award [KC0402010, DE-AC05-00OR22725]
  3. DOE Office of Science by Argonne National Laboratory [DE-AC02-06CH11357]
  4. National Science Foundation [DMR-1508249]

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The relaxation dynamics of PS/silica nanocomposites were studied, and it was found that nanoparticle aggregation enhances the mechanical properties, while nanoparticle loading accelerates structural anisotropy relaxation.
The relaxation dynamics of polystyrene (PS)/silica nanocomposites after a large step deformation are studied by a combination of small-angle scattering techniques and rheology. Small-angle X-ray scattering measurements and rheology show clear signatures of nanoparticle aggregation that enhances the mechanical properties of the polymer nanocomposites (PNCs) in the linear viscoelastic regime and during the initial phase of stress relaxation along with accelerated relaxation dynamics. Small-angle neutron scattering experiments under the zero-average-contrast condition reveal, however, smaller structural anisotropy in the PNCs than that in the neat polymer matrix, as well as accelerated anisotropy relaxation. In addition, the degrees of anisotropy reduction and relaxation dynamics acceleration increase with increasing nanoparticle loading. These results are in sharp contrast to the prevailing viewpoint of enhanced molecular deformation as the main mechanism for the mechanical enhancement in PNCs. Furthermore, the observed acceleration of stress relaxation and reduction in structural anisotropy point to two types of nonlinear effects in the relaxation dynamics of PNCs at large deformation.

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