In Situ Monitoring of Mechanofluorescence in Polymeric Nanofibers

Mechanofluorescent polymers represent a promising class of materials exhibiting fluorescence changes in response to mechanical stimuli. One approach to fabricating these polymers involves incorporating aggregachromic dyes, whose emission properties are governed by the intermolecular distance, which can, in turn, be readily altered by microstructural changes in the surrounding polymer matrix during mechanical deformation. In this study, a mechanofluorescent additive featuring excimer-forming oligo(p-phenylene vinylene) dyes (tOPV) is incorporated into electrospun polyurethane fibers, producing mats of fibers with diameters ranging from 300 to 700 nm. The influence of the additive concentration and fiber orientation on the mechanofluorescent response under tensile deformation is investigated. In situ fluorescence spectroscopy and microscopy imaging reveal a strain-dependent change of the fluorescence color from orange to yellow or green, with a more pronounced response in prealigned fibers. Stresses experienced by the nanofibers during elongation are mapped in real-time. The data reveal that forces initially concentrate in fibers that are aligned parallel to the applied strain, and only later redistribute as other fibers once they also align. These findings advance the understanding of force transfer within fibrous polymer mats and are expected to facilitate the development of self-reporting nanofibers for applications in load-bearing devices, wearable technologies, and mechanochromic textiles.