Probing the Mullins Effect in Filled Elastomers by Small Angle X-ray and Neutron Scattering

While there has been considerable effort made to understand and model the effect that filler particles have on the mechanical properties of filled elastomers, the origins of a striking characteristic strain softening known as the Mullins Effect are still debated. Several micro-mechanical models have been proposed using a variety of mechanisms to describe the polymer-filler and filler-filler interactions to fit mechanical test data without any direct observation of microstructural changes. Small angle x-ray and neutron scattering provide complimentary methods for observing these changes on the relevant length and time scales necessary for identifying and characterizing the proposed mechanisms. We designed and built a modular uniaxial load frame for use in a variety of lab and user facilities. Its capabilities include a 350mm of symmetrical travel and a non-contact strain measurement system using speckle pattern digital image correlation. The system was developed and tested on silica-filled polydimethylsiloxane (PDMS) and polyphenylmethylsiloxane (PPMS) elastomers using the Low Q Diffractometer at the Los Alamos Neutron Science Center at Los Alamos National Laboratory.