Aging in a filled polymer: coherent small angle x-ray and light scattering
1Laboratoire de Spectrometrie Physique, CNRS UMR No. 5588, Universite Joseph Fourier de Grenoble, Boite Postale 87, 38402 St. Martin d'Heres, France.
Summary
Small angle scattering studies reveal that fumed silica aggregates in poly(dimethyl siloxane) form structures that break down with stress. These structures reform over time through diffusion-controlled processes.
Area of Science:
- Materials Science
- Polymer Science
- Colloid Science
Background:
- Fumed silica aggregates in polymer melts form complex structures.
- Understanding their dynamic behavior is crucial for material properties.
Purpose of the Study:
- To investigate the dynamics of fumed silica aggregates in a poly(dimethyl siloxane) melt.
- To characterize the relaxation processes and diffusion mechanisms.
Main Methods:
- Small angle coherent X-ray scattering (SAXS)
- Small angle dynamic light scattering (DLS)
- Mechanical stirring and thermal treatment
Main Results:
- At rest, hydrophilic silica forms weakly bound superstructures, while hydrophobic silica forms a thixotropic paste.
- Both systems exhibit liquid-like diffusion and structural relaxation (flocculation).
- Hydrophilic silica shows faster relaxation rates (5x10⁻¹⁴ cm²/s and 2x10⁻¹⁵ cm²/s) than hydrophobic silica (2x10⁻¹⁵ cm²/s and 9x10⁻¹⁶ cm²/s).
Conclusions:
- The dynamics are governed by diffusion-controlled liquid-like motion and aggregation.
- Surface properties (hydrophilic vs. hydrophobic) significantly influence the dynamics and structure formation.
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