18 research outputs found
Diffusion-controlled radiochemical oxidation of bisphenol A polysulfone
The radiochemical degradation of bisphenol A polysulfone was investigated under a γ-ray dose rate of 24 kGy h-1 up to 30.7 MGy total absorbed dose at 60 °C using gel permeation chromatography, sol-gel analysis, glass transition and rheometry measurements, and oxidation profile measurements by microscopy coupled with Fourier transform infrared analysis in attenuated total reflectance mode. Thin (200 μm) and thick (2 mm) samples were compared. Thin samples undergo mainly chain scissions whereas thick ones undergo mainly crosslinking. The thickness of oxidized layers and, radiochemical yields for chain scissions, crosslinking, oxygen absorption and radical formation were tentatively determined from experimental data in order to determine the influence of oxidative processes on radiochemical ageing and to establish the nature of the crosslinking reactions
Radiochemical ageing of poly(ether ether ketone)
Thin (60 μm) and thick (250 μm) samples of poly(ether ether ketone) were subjected to radiochemical ageing at 24 kGy h -1 dose rate for doses up to 30.7 MGy at 60 °C in air. FTIR spectrophotometry (hydroxyl and carbonyl build-up), ATR microscopy (oxidation profiles), ammonia gaseous treatment (determination of carbonyl nature), density, DSC (glass transition temperature, cold crystallization and melting point changes), and gel content measurements (crosslinking) were conducted for examination of polymer degradation. Thin samples were shown to undergo principally chain scission process whereas thick ones undergo mainly crosslinking. This difference can be attributed to the kinetic control of oxidation by oxygen diffusion. A mechanistic scheme was proposed from radiochemical yields estimations
Atomic-Level Description of Thermal Fluctuations in Inorganic Lead Halide Perovskites
A comprehensive microscopic description of thermally induced distortions in lead halide perovskites is crucial for their realistic applications, yet still unclear. Here, we quantify the effects of thermal activation in CsPbBr3 nanocrystals across length scales with atomic-level precision, and we provide a framework for the description of phase transitions therein, beyond the simplistic picture of unit-cell symmetry increase upon heating. The temperature increase significantly enhances the short-range structural distortions of the lead halide framework as a consequence of the phonon anharmonicity, which causes the excess free energy surface to change as a function of temperature. As a result, phase transitions can be rationalized via the soft-mode model, which also describes displacive thermal phase transitions in oxide perovskites. Our findings allow to reconcile temperature-dependent modifications of physical properties, such as changes in the optical band gap, that are incompatible with the perovskite time- and space-average structures
Jahn-Teller effects in initial and final states: high-resolution X-ray absorption, photoelectron and Auger spectroscopy of allene
Carbon K-edge resonant Auger spectra of gas-phase allene following excitation of the pre-edge 1s → π* transitions are presented and analysed with the support of EOM-CCSD/cc-pVTZ calculations. X-Ray absorption (XAS), X-ray photoelectron (XPS), valence band and non-resonant Auger spectra are also reanalysed with a series of computational approaches. The results presented demonstrate the importance of including nuclear ensemble effects for simulating X-ray observables and as an effective strategy for capturing Jahn-Teller effects in spectra
Transient grating spectroscopy on a DyCo thin film with femtosecond extreme ultraviolet pulses
Surface acoustic waves (SAWs) are excited by femtosecond extreme ultraviolet
(EUV) transient gratings (TGs) in a room-temperature ferrimagnetic DyCo
alloy. TGs are generated by crossing a pair of EUV pulses from a free electron
laser (FEL) with the wavelength of 20.8\,nm matching the Co -edge, resulting
in a SAW wavelength of \,nm. Using the pump-probe transient grating
scheme in a reflection geometry the excited SAWs could be followed in the time
range of -10 to 100\,ps in the thin film. Coherent generation of TGs by
ultrafast EUV pulses allows to excite SAW in any material and to investigate
their couplings to other dynamics such as spin waves and orbital dynamics
Hitting the target: fragment screening with acoustic in situ co-crystallization of proteins plus fragment libraries on pin-mounted data-collection micromeshes
A method is presented for screening fragment libraries using acoustic droplet ejection to co-crystallize proteins and chemicals directly on micromeshes with as little as 2.5 nl of each component. This method was used to identify previously unreported fragments that bind to lysozyme, thermolysin, and trypsin
Quantifying Photoinduced Polaronic Distortions in Inorganic Lead Halide Perovskites Nanocrystals
The development of next generation perovskite-based optoelectronic devices
relies critically on the understanding of the interaction between charge
carriers and the polar lattice in out-of-equilibrium conditions. While it has
become increasingly evident for CsPbBr3 perovskites that the Pb-Br framework
flexibility plays a key role in their light-activated functionality, the
corresponding local structural rearrangement has not yet been unambiguously
identified. In this work, we demonstrate that the photoinduced lattice changes
in the system are due to a specific polaronic distortion, associated with the
activation of a longitudinal optical phonon mode at 18 meV by electron-phonon
coupling, and we quantify the associated structural changes with atomic-level
precision. Key to this achievement is the combination of time-resolved and
temperature-dependent studies at Br K-edge and Pb L3-edge X-ray absorption with
refined ab-initio simulations, which fully account for the screened core-hole
final state effects on the X-ray absorption spectra. From the temporal
kinetics, we show that carrier recombination reversibly unlocks the structural
deformation at both Br and Pb sites. The comparison with the
temperature-dependent XAS results rules out thermal effects as the primary
source of distortion of the Pb-Br bonding motif during photoexcitation. Our
work provides a comprehensive description of the CsPbBr3 perovskites
photophysics, offering novel insights on the light-induced response of the
system and its exceptional optoelectronic properties.Comment: Main: 27 pages, 4 figures SI: 16 pages, 8 figure
The structure of the extended E2 DNA-binding domain of the bovine papillomavirus-1
Bovine papillomavirus proteins were extensively studied as a prototype for the human papillomavirus. Here, the crystal structure of the extended E2 DNA-binding domain of the dominant transcription regulator from the bovine papillomavirus strain 1 is described in the space group P3121. We found two protein functional dimers packed in the asymmetric unit. This new protein arrangement inside the crystal led to the reduction of the mobility of a previously unobserved loop directly involved in the protein-DNA interaction, which was then modeled for the first time.Fil: Leroy, Ludmila. Universidade Federal de Minas Gerais; BrasilFil: Ribeiro Gonçalves Barbosa, João Alexandre. Universidade do BrasÃlia; BrasilFil: de Prat Gay, Gonzalo. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones BioquÃmicas de Buenos Aires. Fundación Instituto Leloir. Instituto de Investigaciones BioquÃmicas de Buenos Aires; ArgentinaFil: Polikarpov, Igor. Universidade de Sao Paulo; BrasilFil: BasÃlio Pinheiro, Carlos. Universidade Federal de Minas Gerais; Brasi
Conical spin order with chiral quadrupole helix in CsCuCl3
Here we report a resonant x-ray diffraction (RXD) study at the Cu L3 edge on
the multi-chiral system CsCuCl3, exhibiting helical magnetic order in a chiral
crystal structure. RXD is a powerful technique to disentangle electronic
degrees of freedom due to its sensitivity to electric monopoles (charge),
magnetic dipoles (spin), and electric quadrupoles (orbital). We characterize
electric quadrupole moments around Cu ascribed to the unoccupied Cu 3d orbital,
whose quantization axis is off the basal plane. Detailed investigation of
magnetic reflections reveals additional sinusoidal modulations along the
principal axis superimposed on the reported helical structure, i.e., a
longitudinal conical (helical-butterfly) structure. The out-of-plane
modulations imply significant spin-orbit interaction despite S = 1/2 of Cu2+.Comment: 17 pages, 5 figure