Steven Earl Kooi

Mechanical failure is a marked limitation for plastics used in structural, protective and coating applications. In particular, perforation under high-rate deformation is difficult to mitigate through conventional molecular design^1,2. Cross-linking is widely used to improve the thermal and chemical stability of polymers, yet under mechanical deformation, it typically renders materials more brittle, limiting impact resistance and functional lifetime³. Overcoming this fundamental trade-off between stability and toughness remains a central challenge. Here we demonstrate that embedding a small fraction of force-sensitive mechanophores as cross-links into common polymers fundamentally reverses this trade-off, producing materials with substantially enhanced ballistic energy dissipation. At strain rates exceeding 10⁷ s^-1, we show that mechanophore-cross-linked networks absorb up to about 115% more energy than conventional thermosets and surpass even their uncross-linked thermoplastic counterparts. We attribute this behaviour to a force- and adiabatic-heating-driven local thermoset-to-thermoplastic transition, in which selective mechanophore scission facilitates viscoplastic deformation at the impact site while preserving network integrity in the surrounding regions. We demonstrate the generality of this strategy in both glassy polystyrene and rubbery styrene-butadiene-styrene triblock copolymers. These results establish mechanophore cross-linking as a design principle for converting commodity polymers into impact-resilient materials and open directions at the intersection of polymer mechanochemistry and extreme-strain-rate material behaviour.

Nanophotonics has revolutionized the control of light-matter interactions in various fields of fundamental science and technology. In this work, we propose Implosion Fabrication (ImpFab) as a versatile nanophotonics fabrication platform providing the highest spatial resolution, material versatility, and full volumetric control. ImpFab uniquely combines top-down lithography with bottom-up nanoparticle assembly within a hydrogel scaffold, enabling precise control over optical material properties, such as refractive index, by adjusting printing parameters. We showcase the potential of ImpFab by fabricating three-dimensional photonic crystals and quasicrystals, as well as demonstrating optical structures with spatially modulated unit cell material properties. Our results highlight the potential of ImpFab in producing nanostructures with tailored optical functionalities, which are crucial for applications in sensing, imaging, and information processing, and opening new avenues in developing non-Hermitian photonic systems with spatially controlled gain and loss.

We present a tabletop method to investigate how tailored laser excitation can enhance shock wave generation in water. By delivering two spatiotemporally separated laser pulses focused into a confined liquid layer, we identify an optimized excitation condition that maximizes the resulting shock pressure. Remarkably, dual-pulse laser excitation leads to an overall shock pressure that far exceeds the sum of the shock pressures generated by the individual pulses. This nonlinear amplification reveals a previously unexploited laser-matter interaction regime that overcomes saturation limits in laser-driven shock generation.

Silica-based glasses have found numerous applications in every field of human endeavor. Understanding their mechanical behavior under high strain rates is essential for the use of these materials in extreme environments. We report on a highly unusual fracture behavior observed in borosilicate glass facilitated by stress-induced molecular rearrangements, allowing the glass to withstand tensile stresses up to 11 GPa. Converging surface acoustic waves (SAW) with controlled amplitude are generated optically and used to investigate the high-strain-rate (10 ⁸ s ⁻¹ ) fracture behavior of borosilicate glass. Above a tensile stress threshold of 6 GPa, fracture of the glass surface is observed, characterized by ejection of material and radial cracking. Unexpectedly, upon further increase of the SAW stress, a second threshold of 8 GPa tensile stress is observed above which the fracture probability dramatically decreases. Raman spectra and nanoindentation measurements of shocked samples indicate significant changes in the topology and coordination numbers of silicon and boron atoms in the amorphous network. These results suggest the ability of thresholded atomic rearrangements to serve as an intrinsic high-strain-rate toughening mechanism for enhanced fracture toughness in amorphous borosilicate glass under dynamic strain conditions.

Connections between magnetic field induced optical activity and chirality have a rich and complicated history. Although the broken inversion symmetry of chiral molecules generates ‘natural’ optical activity, magnetic optical activity is generated by breaking time reversal symmetry. Therefore, molecular chirality is not expected to influence magnetic optical phenomena, such as Faraday rotation. Here we show that the chiral supramolecular assembly of polymers can result in large Faraday effects (Verdet constants = 10 ⁵ °T ^–1 m ^–1 ). This strong Faraday rotation, which is amongst the highest value known for organic materials, originates from the so-called Faraday B term. Typically, B term Faraday responses are weak. We demonstrate large amplification through excitonic coupling within the supramolecular assembly, where the chirality of the system controls the assembly formed. These observations provide an alternative means to enhance the Faraday rotation of low symmetry systems and clarify the role of chirality in previous reported materials.

The connection between magnetic field induced optical activity and chirality has a rich and complicated history. Although the broken inversion symmetry of chiral molecules generates ‘natural’ optical activity, magnetic optical activity is generated by breaking of time reversal symmetry. As a result, molecular chirality is not expected to influence magnetic optical phenomena, such as Faraday rotation. Here we show that the chiral supramolecular assembly of polymers can result in a large Faraday effect. This strong Faraday rotation, which is amongst the highest value known for organic materials, originates from the so-called Faraday B term. Typically, B term Faraday responses are weak. We demonstrate large amplification through excitonic coupling within the supramolecular assembly, where the chirality of the system controls the assembly formed. These observations provide an alternative means to enhance the Faraday rotation of low symmetry systems and clarify the role of chirality in previous reported materials. Tuneable magneto-optical phenomena in low-cost organic materials opens the door to applications including safety testing, bioimaging and quantum information processing

Scintillators convert X-ray energy into visible light and are critical for imaging technologies. Their widespread use relies on scalable, high-quality manufacturing methods. Nanophotonic scintillators, featuring wavelength-scale nanostructures, can offer improved emission properties such as higher light yield, shorter decay times, and enhanced directionality. However, achieving scalable fabrication of these structures remains challenging. Here, we present a scalable fabrication method for large-area nanophotonic scintillators based on the self-assembly of chalcogenide glass photonic crystals. This technique enables the production of nanophotonic scintillators over wafer-scale areas, achieving a six-fold enhancement in light yield compared to unpatterned scintillators. By studying surface nanofabrication disorder, we show its impact on imaging performance and provide a route towards scintillation enhancements without compromising resolution. We demonstrate the practical applicability of our nanophotonic scintillators through X-ray imaging of biological and inorganic specimens. Our results could enable the industrial implementation of a new generation of nanophotonic-enhanced scintillators.

In conventional laser-driven shock experiments, an out-of-plane shock wave is launched and is typically detected interferometrically after it propagates through the sample. In such experiments, the target materials are unavoidably optically damaged at each laser shot. This necessitates changing targets after laser exposure, lowering the shot-to-shot reproducibility and data quality. Here we present a Sagnac interferometer combined with an echelon that can split a single femtosecond probe into many beams, very well adapted for single-shot interferometric characterization of laser-induced shock waves. The echelon provides a 10 ps time resolution and a full time window of about 150 ps. The simplicity, stability, and sensitivity of the single-shot Sagnac interferometer technique ease the thorough characterization of picosecond to nanosecond shock waves, specifically for samples available in limited quantities or for samples that are not uniform from one region to the next.