Visualization of Bond Scission due to Nucleation and Growth of Gas Bubbles in Elastomers.

When an elastomer is saturated with gas and then rapidly decompressed, small cavities may nucleate, inflate, and deflate inside the material. This phenomenon, herein considered as a type of cavitation, is very important for elastomer seals because it induces dam-age and hampers their lifetime in use. By incorporating {\pi}-extended anthracene-maleimide adducts, a damage-activated probe, in a model unfilled poly(ethyl-acrylate) elastomer, we are able to thoroughly visualize where molecular damage occurred due to this rapid decompression. These probes yield a strong and stable fluorescent signal upon polymer chain scission enabling non-destructive detection of damage via confocal fluorescence microscopy in pristine-looking specimens. Cavities nucleated by rapid decompression of a hydrogen-saturated elastomer were examined with the present methodology. We observe that each spherical cavity in its inflated state corresponds in its unloaded configuration to a randomly oriented 2D penny-shape crack. As a result, cavity growth in elastomers occurs through a localized fracture process with irreversible bond breakage and subsequent defor-mation of the initially planar damaged area into a cavity. High resolution inspection of the morphology of these penny-shape cracks suggests that cavity growth may proceed discontinuously and in a stick-slip fashion with stable and unstable crack growth. This novel visualization method has enormous potential for non-destructive inspection of complex 3D damage inside soft materi-als where surface tension and elastic restoring forces close cracks in the absence of loading