Mechanophore activation in a crosslinked polymer matrix via instrumented indentation*

Scratches in transparent polymer coating and barrier layers can cause a host of problems, impacting optical (haze, light transmission, etc.) and mechanical properties (permeability, structural integrity, etc.) The primary focus of this project is to investigate the mechanical activation of a mechanophore (MP)-containing transparent polymer coating. Taking advantage of the amine functionality present in a polyetheramine/bisphenol A epoxy network, we have covalently attached a commercially available Rhodamine dye into a transparent, thermoset polymer. Utilizing the scratch profiles available on a typical nanoindenter, the load was varied so that a transition between ductile (plastic) to brittle deformation was observed within a single scratch. Subsequent fluorescence imaging of the MP-epoxy surfaces revealed the extent of fluorescence activation induced by the mechanical deformation. It has been shown that the Rhodamine-based mechanophore can be used to identify brittle fracture and local stress concentrations prior to macroscopic failure. Fluorescence lifetime and hyperspectral imaging of damage zones provide additional insight into the local deformation around each scratch.