Nanomechanical and chemical characterization of degradation and cross-linking in UV exposed polystyrene.

摘要

A thorough understanding of the chemical and mechanical changes that occur when polymers degrade can contribute to the improving of polymer devices and materials. However, most studies of polymer membrane degradation have focused on chemical changes that occur rather than mechanical and physical changes. In this study nanoindentation and chemical analyses including DRIFTS, contact angle measurement and toluene dissolution were conducted and compared to fully understand the changes that occurred in UV exposed polystyrene. Indentation data displayed an increase in hardness and plain strain modulus increased by 112% and 45% respectively from 0 to 4 hours of exposure, and showed a decrease by 67% and 19% between exposures of 4 hours and 96 hours. Chemical properties analysis revealed that near surface cross-linking increased from 0 to 4 hours before reaching equilibrium while near surface degradation increased continually throughout all exposure times. It was determined that for short exposure times (≤ 4 hours) mechanical properties are more heavily influenced by cross-linking than degradation, and at longer exposure times (> 4 hours) degradation becomes the chemical effect with a greater influence. Nanoindentation was found to be a valuable tool for investigating surface level changes in polymeric materials due to environmental degradation.