A comparison of NMR measurements of residual dipolar couplings in aged silica-PDMS composite materials

摘要

Silica-filled polydimethylsiloxane (PDMS) composite systems are of broad appeal due to their chemical and environmental resilience and the availability of a wide range of tailorable chemical and mechanical properties. These composite materials are generally thought to be stable for decades against numerous stress inducing aging mechanisms including thermal and mechanical loading and environmental, radiative, and chemical attack. The mechanical property changes associated with multi-mechanism aging may be subtle, however, and may not necessarily change linearly as a function of time in service. Since such linear relationships are often used in service lifetime predictions, there is a fundamental need to employ sensitive methods to investigate the structural and motional changes that occur in these materials as a result of aging in harsh environments in which multiple degradation mechanisms may be active. Ideally, these methods would allow a complete assessment of aging mechanisms in order to yield predictive capabilities.