Sub-Micrometer Mechanochromic Inclusions Enable Strain Sensing in Polymers

Blending different types of polymers with traces of a telechelic macromolecule that is end-functionalized with excimer-forming chromophores affords materials that display a highly sensitive, reversible, and strain-dependent mechanochromic response. Confocal microscopy imaging reveals that the additive forms discrete, phase-separated inclusions in host polymers such as poly(& epsilon;-caprolactone), poly-isoprene, poly(styrene-b-butadiene-b-styrene), and different thermoplastic polyurethanes. A comprehensive analysis shows that the mechanochromism of the blends originates from the distortion of the inclusions, which, independent of the additive content and chemical composition of the matrix, deform homogeneously and reversibly in response to the applied macroscopic strain. These findings support the conclusion that such excimer-forming, telechelic macromolecules can be used as universal additives that allow the straightforward fabrication of a wide range of mechanochromic materials.