Ex-situ surface analysis of impact sites on MA-BCP films. (c–e) AFM phase images show the effects of impact at velocities of 407 m/s, 414 m/s, and 515 m/s, respectively. (f–h) FM images that correspond to the contact regions depicted in (c–e). Courtesy of Mechanochemically responsive polymer enables shockwave visualization.
By combining mechanochemistry and microballistic testing, they analyzed the mechanical properties of these materials under extreme conditions. But how did they achieve this?
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The key lies in mechanophores—molecules that respond to mechanical loads by emitting optical signals. When deformation breaks their chemical bonds, they undergo a chemical transformation. This change appears as a color shift, fluorescence, or small molecule release. Integrating them into polymeric materials captures impulsive deformation with unprecedented spatial and temporal resolution. Other techniques cannot achieve this level of precision.
Leveraging this innovation, the researchers developed a copolymer with mechanophores. This material enables direct visualization and quantification of responses under extreme strain rates. Their tests revealed a key finding: transitioning from the plastic regime to a shockwave-dominated behavior in high-velocity impacts.
The image illustrates the chemical and structural characterization of the polymer with mechanophores known as MA-BCP material. (a) Mechanophore activation upon MA bond rupture due to mechanical deformation. (b) Schematic of the diblock copolymer with MA mechanophore between PIB and PS blocks. (c) AFM phase image showing PS spherical domains within the PIB matrix. Inset scale bar: 100 nm. Courtesy of Mechanochemically responsive polymer enables shockwave visualization.
Microscopic fluorescence (FM) tests combined with finite element analysis (FEA) showed that the material’s mechanophores activate not only on the impact surface but also in deeper layers. However, the most surprising discovery was the formation of a Mach cone. This suggests that the impact energy propagated at a speed higher than the shear wave but lower than the longitudinal wave velocity of the material.
The image visualizes shock deformation in MA-BCP films. (a) A 3D projection shows the mechanophore-activated volume beneath the impact site at vi = 414 m/s. (b) A 2D slice reveals a Mach cone-like shape. The dashed red line marks the deformed film surface (measured by AFM), with a 5 μm scale bar. Courtesy of Mechanochemically responsive polymer enables shockwave visualization.
These findings have redefined existing theories on polymer behavior under high-velocity impacts. They have bridged the perspectives of geophysicists and engineers. This research shows that, under extreme strain rates, the plastic regime and shockwaves play a crucial role in energy dissipation.
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This study paves the way for future studies. Moreover, applying mechanophores to other materials could provide deeper insights into their behavior under various impact conditions across different industries. These discoveries could shape the next generation of materials designed to withstand extreme impact conditions.
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