Correlating Fluorescence and Stress/Strain for Spiropyran Mechanosensors

Abstract

When designing mechanical components, they commonly undergo multiple modeling phases for stress determination using analytical or numerical methods like the Finite Element Method (FEM). This is followed by experimental validation performed via stress mapping to identify and account for possible mechanical failure within the design phase. Among the experimental stress mapping techniques, mechanosensing is gaining rapidly increasing attention by research and industry. Mechanosensing is a chemistry-based technique that utilizes molecules called mechanophores. When mechanophores are embedded in transparent polymers, they act as mechanical probes sensing stress/strain throughout the polymer by emitting fluorescence under deformation. While studies have shown the capabilities of mechanophores as stress/strain probes qualitatively, it is currently not known how the mechanophore activation is correlated with the stress/strain-based quantities from a solid mechanics perspective. This study addresses this problem from a phenomenological viewpoint to fill the research area gap. In this work, using a uniaxial tensile testor, experiments are conducted on a Polydimethylsiloxane (PDMS) with a mechanophore spiropyran embedded homogeneously in the bulk of the polymer. The fluorescence data captured in the tests is correlated with the numerically obtained continuum mechanics stress/strain quantities. These correlations will be useful in giving directions towards research in the fundamental understanding of the mechanics of mechanophores, thereby bridging the gap between chemistry and mechanics of mechanosensors. This will pave the way towards optical-only in-situ measurements of stress-strain behavior.