Reversible restructuring of supported Au nanoparticles during butadiene hydrogenation revealed by operando GISAXS/GIWAXS.

Periodically arranged, monodisperse gold nanoparticles supported on flat silicon substrates were studied for the hydrogenation of 1,3-butadiene under operando conditions using Grazing Incidence Small- and Wide-Angle X-ray Scattering (GISAXS/GIWAXS). It was found that the composition and shape of the nanoparticles depends very much on the chemical environment; the particles are shown to be dynamic, undergoing reversible size and shape change particularly during catalytic reaction, highlighting a dynamism often not observed in traditional studies. Specifically, the size of the Au nanoparticles increases during butadiene hydrogenation and this is attributed to the partial removal of a Au2O3 at the metal-oxide interface and consequential shape change of the nanoparticle from a more hemispherical particle to a particle with a larger height to width ratio.

High-resolution thermal imaging with a combination of nano-focus X-ray diffraction and ultra-fast chip calorimetry.

A microelectromechanical-systems-based calorimeter designed for use on a synchrotron nano-focused X-ray beamline is described. This instrument allows quantitative DC and AC calorimetric measurements over a broad range of heating/cooling rates (≤100000 K s(-1)) and temperature modulation frequencies (≤1 kHz). The calorimeter was used for high-resolution thermal imaging of nanogram-sized samples subjected to X-ray-induced heating. For a 46 ng indium particle, the measured temperature rise reaches ∼0.2 K, and is directly correlated to the X-ray absorption. Thermal imaging can be useful for studies of heterogeneous materials exhibiting physical and/or chemical transformations. Moreover, the technique can be extended to three-dimensional thermal nanotomography.

Non-radial growth of helical homopolymer crystals: breaking the paradigm of the polymer spherulite microstructure.

Radial symmetry is essential for the conventional view of the polymer spherulite microstructure. Typically it is assumed that, in the course of the spherulite morphogenesis, the lamellar crystals grow radially. Using submicron X-ray diffraction, it is shown that in banded spherulites of poly(propylene adipate) the crystals have the shape of a helix with flat-on crystals winding around a virtual cylinder of about 6 µm in diameter. The helix angle of 30° implies that the crystal growth direction is tilted away from the spherulite radius by this angle. The implications of the helical crystal shape contradict the paradigm of the spherulitic microstructure. The radial growth rate of such spherulites does not correspond to the crystal growth rate, but to the propagation rate of the virtual cylinder the ribbons wind around.