Abstract
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.
| Original language | English |
|---|---|
| Pages (from-to) | 8867-8884 |
| Number of pages | 18 |
| Journal | Soft Matter |
| Volume | 18 |
| Issue number | 46 |
| DOIs | |
| State | Published - Oct 31 2022 |
Funding
This work was supported, in part, by the Ralph E. Powe Junior Faculty Enhancement Awards from Oak Ridge Associated Universities (S. C.). Y. W. acknowledges support by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Early Career Research Program Award KC0402010, under contract DE-AC05-00OR22725. Part of this work was performed at the Oak Ridge National Laboratory's Center for Nanophase Materials Sciences, which is a DOE Office of Science User Facility. The SAXS measurements were performed at Beamline 12-ID-B of Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. Access to NGB 30m SANS was provided by the Center for High Resolution Neutron Scattering, a partnership between the National Institute of Standards and Technology (NIST) and the National Science Foundation under Agreement No. DMR-1508249. Certain commercial equipment, instruments, or materials are identified in this document. Such identifications do not imply recommendation or endorsement by the NIST nor does it imply that the products identified are necessarily the best available for the purpose. We thank Matthew Melton for help on the SEM measurements.