Using Mechanochemistry to Visualize the Microballistic Impact of Block Copolymer Films

Current measurement platforms for studying the high-strain-rate impact properties of materials remain limited as they cannot experimentally capture the in-situ deformation behavior of the material with the requisite temporal (ns scale) and spatial (sub-μm scale) resolution. In this work, we address this challenge by studying the microballistic response of an anthracene-based mechanophore-functionalized diblock copolymer material system. Upon rupture of the covalent bond due to a high-velocity impact, this mechanophore exhibits a fluorescence signature that scales with the impact velocity. To demonstrate the utility of this mechanophore for studying the high-strain-rate material response, we impact this material system with microprojectiles at impact velocities ranging from 100 to 500 m/s. AFM measurements reveal permanent deformation at the surface of the impacted sites, indicating that plastic deformation is one of the energy dissipation mechanisms. However, laser scanning confocal microscopy reveals fluorescence information well below the deformed surfaces. More importantly, this subsurface deformation volume resembles a Mach cone that is confirmed by simulations, thus suggesting the significant role of acoustic wave attenuation for energy dissipation in these materials. Finally, we demonstrate that this mechanophore system allows for the three-dimensional visualization of the deformation volume of the material that scales with the impact velocity, thus providing results that cannot be imaged otherwise and offering new insights into microballistic impact studies.