Sensitivity of Carbon Nanotubes to the Storage of Stress in Polymers

Residual stress in polymers arises from the freezing of unstable molecular conformations. Residual stress is critical because its relaxation can cause shrinkage, defects, and fractures of polymer materials. The storage of stress is purposely enhanced to develop shape memory materials. Unfortunately, the storage of mechanical stress is still poorly controlled and understood. An approach to sense the storage of stress based on the spectroscopic response of carbon nanotubes is explored. The Raman response of nanotubes exhibits a variable sensitivity to strain when embedded in polymers that have experienced different thermal and mechanical treatments. This unique feature opens up new possibilities for the use of carbon nanotubes as mechanical nanosensors. Residual stress is ubiquitous in most polymer technologies. It can cause undesired deformations, defects, or be sought after for shape memory phenomena. It is shown that the Raman response of carbon nanotubes in polymers strongly varies as a function of the stress stored by the polymer, thus providing a new tool for sensing residual stress.