ABSTRACT
We present in situ pressure experiments on aluminogermanate nanotubes studied by X-ray scattering and absorption spectroscopy measurements. Structural transformations under hydrostatic pressure below 10 GPa are investigated as a function of the morphology, organization, or functionalization of the nanotubes. Radial deformations, ovalization for isolated nanotubes, and hexagonalization when they are bundled are evidenced. Radial collapse of single-walled nanotubes is shown to occur, in contrast to the double-walled nanotubes. The effect of the transmitting pressure medium used on the collapse onset pressure value is demonstrated. Axial Young's moduli are determined for isolated (400 GPa) and bundled (600 GPa) single-walled nanotubes, double-walled nanotubes (440 GPa), and methylated single-walled nanotubes (200 GPa).
ABSTRACT
A compact active x-ray beamstop has been developed for the SWING beamline at Synchrotron SOLEIL with two main functions, blocking the x-ray beam directly transmitted by the sample to protect the Dectris EigerX4M 2D detector and monitoring its intensity. The beamstop is composed of a sensor inserted in a well of tungsten carbide. The sensor is based on a piece of free-standing single crystal chemical vapor deposited diamond used in the ionization chamber mode. The beamstop has been installed on the beamline detector stage within the detection vacuum chamber, just upstream of the large 2D detector. The intensity monitoring performance (rms noise over signal) is shown to be better than 0.06% and the linearity is shown to be better than 2% for over more than five decades. The beamstop has been calibrated between 5 and 16 keV to provide the photon flux measurements in absolute units (ph/s). The specific design of the beamstop increases the small-angle x-ray scattering q-range by a factor of 1.5 in the low angle side, as compared to the previous active beamstop, based on a more standard commercial Si diode. The beamstop has been available for three years for SWING user operation (5-17 keV). It is fully compatible with the different beamline operating modes and fluxes, except in the microbeam mode, where the very divergent beam becomes too large at the beamstop position, and the previous, larger, beamstop is then more appropriate.
ABSTRACT
We designed a nanocomposite consisting of CdSe nanoplatelets dispersed in the form of short stacks in the polybutadiene domains of a polystyrene-polybutadiene-polystyrene (SBS) thermoplastic elastomer matrix. Under strain, the material displays reversible, macroscopic anisotropic properties, e.g. the fluorescence signal. We present here a structural study of the composite under stretching, by in situ high-resolution X-ray scattering using synchrotron radiation. Modelling the scattering signal allows us to monitor the evolution of both the matrix and the platelets under strain. In particular, we show that the strain "reshuffles" the platelet stacks, which tilt their long axis from parallel to the plane of the microstructure lamellae at rest to perpendicular to this plane at high strain, at the same time breaking into smaller pieces, more easily accommodated in the soft butadiene domains. This reshuffling is fully reversed after strain relaxation. Moreover, it can be prevented by adding free oleic acid, which reinforces the interactions between the platelets in the stacks.
ABSTRACT
Herein, we describe the self-assembling of gold nanorods (GNRs) induced during the ligand exchange at their surface. An exchange reaction between tricysteine PEGylated peptidic ligands and cetyltrimethylammonium bromide (CTAB)-protected gold nanorods is conducted. We demonstrated that the terminal group charge (positively or negatively charged) and the hydrophobicity of the peptidic ligands (bearing or not an undecanoyl chain) strongly affects the self-organization of the GNRs occurring in solution. Adjusting the amount of short PEGylated peptides causes a self-organization of the gold nanorods in solution, resulting in a red- or blue-shift of the plasmon bands. The decrease of their surface charge and the self-assembling in solution were first shown by zetametry, by Dynamic Light Scattering and UV-spectroscopy. Thanks to Small Angle X-ray Scattering experiments and Transmission Electron Microscopy images, the self-organization of the nanorods in solution was clearly demonstrated and correlated to the spectroscopic change in absorbance. Conversely, in the case of longer PEGylated peptidic ligands including an undecanoyl chain, the GNRs are particularly stable against aggregation for several days after purification. By controlled drying on a substrate, we showed their ability to self-organize into well-defined ordered structures making them very attractive as building blocks to design optical materials.
