Summary Thermosets play a key role in the modern plastics and rubber industries, comprising ~20% of polymeric materials with a worldwide annual production of ~65 million tons. 1 , 2 The high density of crosslinks that gives thermosets their useful properties ( e.g ., chemical/thermal resistance, and tensile strength) comes at the expense of degradability and recyclability. Here, using the industrial thermoset polydicyclopentadiene (pDCPD) as a model system, we show that when a small number of cleavable bonds are selectively installed within the strands of thermoset plastics, the resulting materials can display the same mechanical properties as the native material, yet they are able to undergo triggered degradation to yield soluble, recyclable products of controlled size and functionality. In contrast, installation of cleavable crosslinks, even at comparably high loadings, does not produce degradable materials. These findings reveal cleavable bond location as a design principle for controlled thermoset degradation. Moreover, a new class of recyclable thermosets poised for rapid deployment is introduced.

The finite spectral line width of an ensemble of CdSe nanocrystals arises from size and shape inhomogeneity and the single-nanocrystal spectrum itself. This line width directly limits the performance of nanocrystal-based devices, yet most optical measurements cannot resolve the underlying contributions. We use two-dimensional electronic spectroscopy (2D ES) to measure the line width of the band-edge exciton of CdSe nanocrystals as a function of radii and surface chemistry. We find that the homogeneous width decreases for increasing nanocrystal radius and that surface chemistry plays a critical role in controlling this line width. To explore the hypothesis that unpassivated trap states serve to broaden the homogeneous line width and to explain its size-dependence, we use 3D ES to identify the spectral signatures of exciton-phonon coupling to optical and acoustic phonons. We find enhanced coupling to optical phonon modes for nanocrystals that lack electron-passivating ligands, suggesting that localized surface charges enhance exciton-phonon coupling via the Fröhlich interaction. Lastly, the data reveal that spectral diffusion contributes negligibly to the homogeneous line width on subnanosecond time scales.

This paper presents a novel approach to launch single microparticles at high velocities under low vacuum conditions. In an all-optical table-top method, microparticles with sizes ranging from a few microns to tens of microns are accelerated to supersonic velocities depending on the particle mass. The acceleration is performed through a laser ablation process and the particles are monitored in free space using an ultra-high-speed multi-frame camera with nanosecond time resolution. Under low vacuum, we evaluate the current platform performance by measuring particle velocities for a range of particle types and sizes, and demonstrate blast wave suppression and drag reduction under vacuum. Showing an impact on polyethylene, we demonstrate the capability of the experimental setup to study materials behavior under high-velocity impact. The present method is relevant to space applications, particularly to rendezvous missions where velocities range from tens of m/s to a few km/s, as well as to a wide range of terrestrial applications including impact bonding and impact-induced erosion. Highlights• A laser-driven microparticle launcher with vacuum capabilities is described • Maximum velocities for particles of different types and masses are reported under atmospheric and low vacuum conditions • Velocities are limited by optical absorption saturation and particle strength and heat resistance • Under vacuum conditions, the blast wave generated upon laser ablation is largely suppressed and drag is reduced • The ballistic limit is measured for a polyethylene film and the residual velocity is modeled using a Recht-Ipson model