Time-resolved Synchrotron X-ray Diffraction Research Articles

Evaluation of molecular interaction between intercellular lipid organization in human stratum corneum and terpenes using time-resolved synchrotron X-ray diffraction

The stratum corneum (SC) presents certain limitations for topical administration of medication, which can be overcome using penetration enhancers (PEs) such as terpene (TP). The SC is also crucial for maintaining the skin barrier and consists of two lamellar structures: the short periodicity phase (SPP) and long periodicity phase (LPP). In this study, we monitored changes in the X-ray diffraction peaks of the human SC, 30 min after TP application (neroridol, 1,8-cineol, and d-limonene). With the application of nerolidol, no significant changes were observed in the small-angle diffraction peak positions for the lamellar structure of SPP, but the integrated intensity decreased. On the contrary, when applying 1,8-cineole and d-limonene, a lower angle peak shift with broadening of the peak width of SPP diffraction peaks was observed for d-limonene than for 1,8-cineole, and the degree of peak shift and width broadening was greater for d-limonene than for 1,8-cineole. The diffraction peaks of LPP disappeared when 1,8-cineole and d-limonene were applied. These results indicate that the degree of interaction between the SC and TP differs depending on the molecular species, and d-limonene and 1,8-cineole exhibit penetration-enhancing via lamellar structure disruption of both SPP and LPP, immediately after application.

Dehydration kinetics of nanoconfined water in beryl probed by high temperature single crystal synchrotron X-ray diffraction

Understanding changes in material properties through external stimuli plays a key role in validating the expected performance of materials and engineering material properties in a controlled manner. Here, we introduce a fundamental protocol to deduce dehydration reactions kinetics of water confined in nanopore channels, with the cyclosilicate beryl as the scaffold of interest, using time-resolved synchrotron X-ray diffraction (SXRD), in the temperature interval of 298–1038 K. The temperature-dependent intensity (I)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$(I)$$\\end{document} of the strongest reflection (112) was used as the crystallite variable. An estimation of an isobaric thermal crystallite coefficient, k\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$k$$\\end{document}, analogous with the isobaric thermal expansion coefficient, established the rate of relative crystallization as a function of temperature, ∂I∂T\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\frac{\\partial I}{\\partial T}$$\\end{document}. A plot of lnk\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$lnk$$\\end{document} and 1T\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\frac{1}{T}$$\\end{document} gives rise to two kinetic steps, indicating a slow dehydration stage up to ~ 700 K and a fast dehydration stage up to the investigated temperature 1038 K. The crystal structure of beryl determined up to 1038 K, in temperature increment as small as 10 K, indicates the presence of channel ions Na and Fe and a gradual decrease of water upon heating.

Real-Time Atomic Scale Kinetics of a Dynamic Event in a Model Ionic Crystal

The mineral CaF2 is the archetype of the α fluorite structure and its high-pressure phase transition to γ cotunnite is an ideal test bed for exploring the effects of kinetics. The inter-disciplinary topic of the kinetics of dynamically driven phase transitions is at the forefront of condensed matter physics, both for its theoretical importance and its relevance to technological applications at extreme conditions of pressure and temperature. Here we probe the α → γ → α structural transformations taking place over the nanosecond timescale of a dynamic event, beginning-to-end: from the principal shock Hugoniot state, followed by a quasi-steady off-Hugoniot release state, and finally the unsteady return to near-ambient conditions. We present quantitative, atomic-scale data of the unfolding of the dynamically driven phase transition and its subsequent reversal close to the α/γ phase boundary. Dynamic loading with a two-stage gas gun is coupled with in situ time-resolved synchrotron X-ray diffraction and with continuum scale velocimetry at the Dynamic Compression Sector (DCS), Advanced Photon Source, Argonne National Laboratory. Our results demonstrate the time dependence of phase transitions and highlight the need for modeling of transition kinetics in dynamically driven processes.

Effect of grain size on amorphization mechanism and kinetics of bridgmanite in shocked meteorites

Bridgmanite formation and amorphization in shocked meteorites constrain the pressure and temperature conditions during planetary impact. However, the effect of the bridgmanite grain size on its amorphization kinetics is still unclear. Here, the amorphization mechanism and kinetics of fine-grained polycrystalline bridgmanite were studied at high temperatures up to 1080 K. High-temperature time-resolved synchrotron X-ray diffraction measurements showed that significant volume expansion due to temperature-induced amorphization caused static stress, which then hindered amorphization progress. Further, the temperature required for the amorphization of fine-grained bridgmanite (~ 1 μm) was found to be approximately 100 K higher than that required for the amorphization of coarse-grained samples (> 10 μm). We also noted that amorphization preferentially commenced at the twin planes and subgrain boundaries of bridgmanite grains, resulting in lower amorphization temperatures for the coarse-grained samples. The limited number of such specific locations in fine-grained natural bridgmanite suggested that grain boundary amorphization may be the dominant mechanism for bridgmanite amorphization in shocked meteorites. This unique amorphization kinetics would support the preservation of bridgmanite during the post-shock annealing in the shocked meteorite. Although bridgmanite amorphization starts easily at temperatures above ~ 420 K, a small amount of bridgmanite grains can survive at temperatures above 800 K by the effect of amorphization-induced stress.

Dynamic electrical response of vortex polarization in (Pb0.9Sr0.1)TiO3/SrTiO3 artificial superlattice thin films

Artificial superlattice thin films with alternative Pb0.9Sr0.1TiO3 (PST) and SrTiO3 layers were fabricated via pulsed laser deposition. The vortex domains were formed by adjusting the unit cell number of the PST layer to be 20. The electrical response measured by time-resolved synchrotron x-ray diffraction with the repeated pulse voltages of a time interval of 1000 μs indicates that the reorientation of dipole moments in the vortex domains is susceptible to the applied electric field and is a reversible process. Although the centrosymmetric vortex domain structure is not considered to exhibit piezoelectricity, an evident change in the out-of-plane lattice constant with the applied electric field was confirmed. The magnitude of the electromechanical response at 600 kV/cm was estimated to be 19 pm/V, which is nearly comparable to the piezoelectric constant d33 of bulk PbTiO3.

Hematite-goethite ratios at pH 2–13 and 25–170 °C: A time-resolved synchrotron X-ray diffraction study

Iron (oxyhydr)oxides are sensitive indicators of pH, Eh, temperature, microbial activity, and climate conditions in the Critical Zone. The most ubiquitous and environmentally significant iron oxides in most soils are two-line ferrihydrite, goethite, and hematite. Here we present a comprehensive study of the transformation of two-line ferrihydrite to hematite and goethite over a wide range of temperature (25–170 °C) and initial pH (2−13) conditions through ex situ batch and in situ synchrotron X-ray diffraction (XRD) experiments.Within the high time resolution of our experiments, goethite and hematite nucleated nearly simultaneously from ferrihydrite in nearly equal concentrations by mass. Hematite increased in abundance relative to goethite until a steady-state ratio was achieved, and both phases ceased growth on the depletion of ferrihydrite. Higher temperatures and lower water activities favored hematite formation at all pH values studied. In both our batch and our time-resolved, angle-dispersive synchrotron X-ray diffraction experiments, hematite was favored relative to goethite at an initial pH of 3 to 5. In contrast, goethite preferentially formed in neutral (initial pH 7–8) and highly alkaline conditions (initial pH ≥ 11). Surprisingly, mildly alkaline conditions (initial pH 9–11) induced the precipitation of a highly Fe-deficient (Feocc = ~0.80–0.90) variety of hematite known as “hydrohematite” in greater concentrations than goethite. Our results are useful for the application of hematite-goethite ratios as paleoclimate proxies for soil and sediment systems with low pH buffering capacities.

Disorder trapping and formation of antiphase nanodomains in Ni3Sn: In situ observation and high resolution characterization

Rapid solidification of the intermetallic Ni3Sn compound from an undercooled liquid was investigated using time-resolved synchrotron X-ray diffraction. Primary growth of an ordered and a disordered cubic solid was observed in situ at a low and a high undercooling, respectively. The disordered cubic solid was reordered after rapid solidification and experienced a solid-state transformation in cooling. A HRTEM study revealed high density of crystal defects and nanodomains in the transformed matrix. A HAADF-STEM study determined that the nanodomains are antiphase domains with chemical disorder. These observations indicated a possibility of online control of mechanical properties in additively manufactured intermetallics.

Dynamic x-ray diffraction and nanosecond quantification of kinetics of formation of β -zirconium under shock compression

We report the atomic- and nanosecond-scale quantification of kinetics of a shock-driven phase transition in Zr metal. We uniquely make use of a multiple shock-and-release loading pathway to shock Zr into the $\ensuremath{\beta}$ phase and to create a quasisteady pressure and temperature state shortly after. Coupling shock loading with in situ time-resolved synchrotron x-ray diffraction, we probe the structural transformation of Zr in the steady state. Our results provide a quantified expression of kinetics of formation of $\ensuremath{\beta}$-Zr phase under shock loading: transition incubation time, completion time, and crystallization rate.

The role of two-stage phase formation for the solid-state runaway reaction in Al/Ni reactive multilayers

While extensively studied for heating rates below 1.7 K/s and above 1000 K/s, the solid-state phase transformations in Al/Ni reactive multilayers have not been examined at intermediate heating rates between 100 K/s and 1000 K/s. Combined nanocalorimetry and time-resolved synchrotron x-ray diffraction studies are utilized to address this range of heating rates for multilayers with an overall composition of 10 at. % Ni and a bilayer thickness of 220 nm. It was found that a two-stage phase formation of Al3Ni proceeds up to a heating rate of 1000 K/s. The two growth stages occur in the solid-state and are kinetically separated. The activation energy of the first growth stage is determined to be 137 kJ/mol, which agrees well with the literature data at low heating rates. At 1000 K/s, a transition to a runaway reaction is observed. Unusual for metallic multilayers, the reaction proceeds completely in the solid-state which is also known as “solid flame.” Using nanocalorimetry, a critical input power density for ignition of 5.8 × 104 W/cm3 was determined. The rapid succession of the two Al3Ni formation stages was identified as the underlying mechanism for the self-sustaining reaction.

Analysis of the reaction runaway in Al/Ni multilayers with combined nanocalorimetry and time-resolved X-ray diffraction

Self-sustaining runaway reactions in reactive multilayers exhibit heat-up with over 106 K/s to temperatures of higher than 1000 °C, which defines unprecedented kinetic regimes for metallurgical phase transformations. The latter allows for developing alternative concepts for microstructure design. In order to explore the phase transformations in these kinetic regimes, we combine nanocalorimetry with time-resolved synchrotron X-ray diffraction. Nanocalorimetry allows us to perform thermal analysis of ignition as well as the reaction runaway and to develop necessary and mandatory quantitative criterions for ignition. In order to trace the temporal phase evolution, we use time-resolved synchrotron X-ray diffraction. We heat the Al/Ni multilayers with 5000 K/s and find that Ni starts to diffuse into the Al layer at 271 °C. Ignition occurs, dependent on the bilayer thickness, at about 400 °C in the solid state and atomic diffusion is revealed as the dominating mechanism. During the runaway, samples heat up in four stages with maximal 106 K/s to 1100 °C. Ni2Al3 is the first phase to form which starts to nucleate once Al melts. The majority of the intermetallic phase grows after the runaway reaction in the fourth stage and reaches its maximum during cooling. This trend of the temporal phase evolution eventually enables us to propose a mechanism exhibiting conceptual similarities with the exothermic dissolution mechanism recently suggested for self-sustaining reaction fronts in Al/Ni multilayers.

The myosin interacting-heads motif present in live tarantula muscle explains tetanic and posttetanic phosphorylation mechanisms

Striated muscle contraction involves sliding of actin thin filaments along myosin thick filaments, controlled by calcium through thin filament activation. In relaxed muscle, the two heads of myosin interact with each other on the filament surface to form the interacting-heads motif (IHM). A key question is how both heads are released from the surface to approach actin and produce force. We used time-resolved synchrotron X-ray diffraction to study tarantula muscle before and after tetani. The patterns showed that the IHM is present in live relaxed muscle. Tetanic contraction produced only a very small backbone elongation, implying that mechanosensing-proposed in vertebrate muscle-is not of primary importance in tarantula. Rather, thick filament activation results from increases in myosin phosphorylation that release a fraction of heads to produce force, with the remainder staying in the ordered IHM configuration. After the tetanus, the released heads slowly recover toward the resting, helically ordered state. During this time the released heads remain close to actin and can quickly rebind, enhancing the force produced by posttetanic twitches, structurally explaining posttetanic potentiation. Taken together, these results suggest that, in addition to stretch activation in insects, two other mechanisms for thick filament activation have evolved to disrupt the interactions that establish the relaxed helices of IHMs: one in invertebrates, by either regulatory light-chain phosphorylation (as in arthropods) or Ca2+-binding (in mollusks, lacking phosphorylation), and another in vertebrates, by mechanosensing.

Thick Filament Activation and Post-Tetanic Potentiation Mechanisms Evolved Differently in Invertebrate and Vertebrate Striated Muscle

Striated muscle contraction involves sliding of actin thin filaments along myosin thick filaments, controlled by calcium through thin filament activation. In relaxation, the two heads of myosin interact with each other to form the interacting-heads motif, consisting of blocked and free heads helically arranged around the filament backbone. A key question is how both free and blocked heads are activated and released from the backbone to approach actin and produce force. In a proposed mechanosensing mechanism for vertebrate striated muscle, a ∼1.4% backbone elongation leads to thick filament activation. We used time-resolved synchrotron X-ray diffraction to determine whether a similar mechanism is present in tarantula striated muscle. Tetanic isometric contraction produced only very small backbone elongation (∼0.27%), much smaller than in frog, suggesting that a mechanosensing mechanism is not of primary importance in tarantula. Rather, thick filament activation is produced by a phosphorylation mechanism, revealed by the X-ray diffraction patterns and force measurements before and after tetanus, correlated with the levels of myosin regulatory light chain phosphorylation. The results provide insights into the mechanism of force potentiation and post-tetanic potentiation. We also show that tarantula (Aphonopelma hentzi) muscle has an additional thermosensing mechanism that disorders the myosin heads above and below 22.5° C. Together, these findings suggest that -apart from insect flight muscle stretch activation - two other molecular mechanisms for thick filament activation have evolved to disrupt the intermolecular interactions that establish the relaxed helices of free and blocked heads: one in invertebrates (with a rigid paramyosin core), by either RLC phosphorylation (as in arthropods) or Ca2+-binding (as in mollusks, that lack phosphorylation), and another in vertebrates (lacking paramyosin), by mechanosensing. Supported by NIH grants AR067279, GM103622, AR072036 and HL139883.

Configurational constraints on glass formation in the liquid calcium aluminate system

We report new time-resolved synchrotron x-ray diffraction (SXRD) measurements to track structural transformations in calcium-aluminate (CaO)x(Al2O3)1−x liquids during glass formation, and review recent progress in neutron diffraction with isotope substitution (NDIS) experiments, combined with aspherical ion model molecular dynamics (AIM-MD) simulations, to identify the atomic-scale configurational constraints on glass-forming ability. The time-resolved measurements reveal substantial changes in ordering on short- and intermediate-range occurring during supercooling. In the equimolar composition x = 0.5 (CA), the liquid undergoes a remarkable structural re-organisation on vitrification as over coordinated AlO5 polyhedra and oxygen triclusters breakdown to form a network of predominantly corner-shared AlO4 tetrahedra. This is accompanied by the formation of branched chains of edge-and face-sharing Ca-centred CaOy polyhedra contributing to cationic ordering on intermediate length-scales. The Ca-rich end-member of the glass-forming system x = 0.75 (C3A) is largely composed of AlO4 tetrahedra, but % unconnected AlO4 monomers and Al2O7 dimers are present, representing a threshold after which the glass can no longer support the formation of an infinitely connected network. Overall, the AIM-MD simulations are in excellent agreement with the SXRD and NDIS experiments suggesting an accurate potential model. However, small discrepancies between the simulated glass structures and experimental measurements are apparent, indicating a small degree of liquid-like ordering persists in the simulated glass trajectories. This may be due to the short simulation time-scales which are unrepresentative of the viscous kinetic processes involved in supercooling and glass formation. One approach to improve future models could be the integration of rare event sampling techniques into MD simulation codes to massively extend equilibration time-scales and more accurately model vitrification and structural configurations in real glass systems.

Nanosecond Optically Induced Phase Transformation in Compressively Strained BiFeO_{3} on LaAlO_{3}.

Above-band-gap optical illumination of compressively strained BiFeO_{3} induces a transient reversible transformation from a state of coexisting tilted tetragonal-like and rhombohedral-like phases to an untilted tetragonal-like phase. Time-resolved synchrotron x-ray diffraction reveals that the transformation is induced by an ultrafast optically induced lattice expansion that shifts the relative free energies of the tetragonal-like and rhombohedral-like phases. The transformation proceeds at interfaces between regions of the tetragonal-like phase and regions of a mixture of tilted phases, consistent with the motion of a phase boundary. The optically induced transformation demonstrates that there are new optically driven routes towards nanosecond-scale control of phase transformations in ferroelectrics and multiferroics.

Mineralogical and geochemical constraints on chromium oxidation induced by birnessite

We have explored redox reactions between dissolved Cr and the phyllomanganate birnessite with high resolution through simultaneous synchrotron X-ray diffraction, X-ray spectroscopy, and fluid analysis at different concentrations of solution pH. Specifically, we collected time-resolved synchrotron X-ray diffraction patterns and X-ray absorption near edge structure (XANES) spectra from triclinic Na-birnessite every 15 min while passing pH controlled 1.0 mM Cr(III) nitrate solutions through a capillary cell. In addition, we quantified Cr(VI) concentrations of the eluate solution every 15 min using spectrophotometry.Consistent with previous studies, we observed an increased rate of Cr(VI) production with decreasing pH. We attribute the comparatively slow kinetics of Cr(III) oxidation at pH 5.0 and 4.0 to a transformation from triclinic to hexagonal birnessite. This solid-state transition reproducibly coincided with a ∼10-fold decline in the extent of oxidation of aqueous Cr(III). Control experiments without Cr(III) revealed no evidence for birnessite transformation within the same time frame, and experiments with hexagonal birnessite as the starting material generated solutions with low fractions (∼3 mol%) of dissolved Cr(VI) from start to finish. At pH 3.0 and 2.0, however, production of Cr(VI) was consistently higher than was observed at pH 5.0 and 4.0. Specifically, at pH 2.0, 80 mol% of the influent Cr(III) was oxidized to Cr(VI) during the experiment compared to 20 mol% at pH 5.0. XANES analyses showed evidence for both Cr(III) and Cr(VI) adsorbing onto the surface of birnessite at all pH values.We propose that Cr(III) is oxidized to Cr(VI) by an electron exchange that reduces Mn(III) in birnessite to Mn(II). At pH 3.5 and higher, the structure of birnessite consequently transforms to hexagonal birnessite. By this pathway, the birnessite crystal structure critically controls the oxidation of dissolved Cr(III) due to the accessibility of reactive Mn(III) in triclinic birnessite relative to hexagonal birnessite. Below pH 3.5, however, birnessite dissolution systematically exposes reactive sites that enable the continuous oxidation of Cr(III) to Cr(VI).

Kinetics of the Atomic Structure of Palladium Nanoparticles during the Desorption of Hydrogen According to X-Ray Diffraction

The process of desorption of hydrogen from small palladium nanoparticles is monitored by time-resolved synchrotron X-ray diffraction. Changes in the diffraction patterns corresponding to the transition from the palladium β-phase to the α-phase are detected with an accuracy of 0.3 s. The model of the continuous change in the size of the β-phase region can be excluded, since the Rietveld analysis does not reveal a broadening of the diffraction peaks corresponding to the palladium lattice during desorption. The theoretical simulation shows the presence of a surface/core interface with different average cell parameters. However, the near-surface layers of the nanoparticle make a lower contribution to the observed diffraction reflections because of a lower crystallinity. The cell parameter in the nanoparticle core depends on the hydrogen concentration both in the core itself and in the shell due to the presence of stresses at the interface.

A kinetic and mechanistic study into the transformation of calcium sulfate hemihydrate to dihydrate.

The conversion of CaSO4·0.5H2O to CaSO4·2H2O is of great importance industrially, being the reaction behind plasterboard production and the setting of medical plasters. A detailed kinetic and mechanistic study of this process was conducted using time-resolved synchrotron X-ray diffraction in this work. The CaSO4·2H2O product is very similar regardless of whether the α- or β-form of CaSO4·0.5H2O is used as the starting material, but the reaction process is very different. The induction time is usually shorter for α-CaSO4·0.5H2O than β-CaSO4·0.5H2O, and a greater conversion percentage is observed with the former (although in neither case does the reaction proceed to 100% completion). The temperature of the system, widely used in industry as an indirect measure of the extent of the hydration process, is found to be a poor proxy for this, with the maximum temperature reached well before the reaction is complete. The Avrami-Erofe'ev and Gualtieri models could both be fitted to the experimental data, with the fits being substantially closer in the case of α-CaSO4·0.5H2O. The rate of reaction in the Avrami model tends to increase with the amount of gypsum seeds added to accelerate the process, and the importance of nucleation declines. The Gualtieri analysis suggested that the rate of nucleation increases substantially with the amount of seeds added, while there are less distinct changes in the rate of crystal growth. At low seed concentrations (<0.5% w/w) the rate of crystal growth is greater than the rate of nucleation, but at concentrations above 0.5% w/w nucleation is faster. These findings represent the first synchrotron study of the conversion of CaSO4·0.5H2O to CaSO4·2H2O, and will be of importance to gypsum producers globally.

In Situ Time-Resolved Phase Evolution and Phase Transformations in U-6 Wt Pct Nb

In situ time-resolved synchrotron X-ray diffraction experiments were conducted to study the fine-scale phase evolution of U-6Nb. Upon rapid heating from 125 °C to 400 °C, a reverse martensitic transformation sequence, α″ → γo → γs, was observed in less than 4 seconds, which represents the first direct observation of the γo → γs transformation in diffraction-based measurements. Consistent with previous ex situ metallography experiments, our isothermal hold experiments at 526 °C, 530 °C and 565 °C reveal two distinct reactions for the phase separation, γs → α-U + γ1 (general precipitation) followed by (α-U + γ1) → α-U + γ1-2 (discontinuous precipitation). For the first-stage precipitation, the incubation time is determined to be ~ 50 and 100 seconds, respectively, for the isothermal aging at 526-530 °C and 565 °C. At this stage, the phase transformation is characterized by the simultaneous growth of α-U and γ1 at the expense of γs. As expected from the Arrhenius equation for the reaction rate, the determined times (~ 23 minutes) for the completion of the first-stage reaction at 526 ± 3 °C and 530 ± 3 °C are nearly twice longer than that at 565 ± 4 °C (~ 13 minutes). Over these periods of time, the Nb contents derived from a Vegard’s-type relationship for γ1 are in the 30.2 to 32.1 and 29.2 to 30.6 at. pct ranges, and the kinetics of the precipitation at 565 ± 4 °C can be described by the classic Avrami rate equation and one-dimensional growth of a surface or grain-boundary nucleation. During the second-stage precipitation, the γ1 phase continues to enrich in Nb as it gradually evolves toward the α + γ1-2 metastable state (up to 47 at. pct over a period of 172 minutes at 530 °C). These new and time-resolved measurements can be used to better constrain the time–temperature–transformation diagram, solute (Nb) redistribution, and transformation kinetics during the early stages of the diffusional phase transformation.

Phase transitions in bismuth under rapid compression**Project supported by the Joint Fund of the National Natural Science Foundation of China and the China Academy of Engineering Physics (NSAF) (Grant No. U1530134), the Foundation of National Key Laboratory of Shock Wave and Detonation Physics, China (Grant No. 6142A0306010817), and the Chinese Academy of Sciences (Grant Nos. KJCX2-SW-N20 and KJCX2-SW-N03).

The structural phase transitions of bismuth under rapid compression has been investigated in a dynamic diamond anvil cell using time-resolved synchrotron x-ray diffraction. As the pressure increases, the transformations from phase I, to phase II, to phase III, and then to phase V have been observed under different compression rates at 300 K. Compared with static compression results, no new phase transition sequence appears under rapid compression at compression rate from 0.20 GPa/s to 183.8 GPa/s. However, during the process across the transition from phase III to phase V, the volume fraction of product phase as a function of pressure can be well fitted by a compression-rate-dependent sigmoidal curve. The resulting parameters indicate that the activation energy related to this phase transition, as well as the onset transition pressure, shows a compression-rate-dependent performance. A strong dependence of over-pressurization on compression rate occurs under rapid compression. A formula for over-pressure has been proposed, which can be used to quantify the over-pressurization.

Poly (3-hydroxybutyrate-co-3-hydroxyvalerate)/cellulose nanocrystal films: artificial weathering, humidity absorption, water vapor transmission rate, antimicrobial activity and biocompatibility

Bionanocomposite films of poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) with different cellulose nanocrystal (CNC) loadings were prepared. Effects of artificial weathering, humidity absorption, water vapor transmission rate (WVTR), antimicrobial activity and biocompatibility were studied. Differential scanning calorimetry (DSC) and time resolved synchrotron X-ray diffraction were used to provide information about the effect of CNC on the crystalline structure of PHBV in the bionanocomposites. The incorporation of CNC accelerated the crystallization rate of PHBV due to a nucleating effect. DSC results showed first a decrease of crystallization and then the occurrence of secondary crystallization after artificial weathering. Scanning electron microscopy images implied well CNC distribution before artificial weathering and formation of blister—like points due to artificial weathering. Hydrophobicity of bionanocomposites was found to be slightly lower than for the PHBV in the humidity absorption tests. Bionanocomposites exhibited smaller WVTR due to restricted PHBV chain mobility. Samples with zinc oxide and silver showed antimicrobial inhibition activities against S. enterica, L. monocytogenes, S. aureus and E. coli. Results of cell viability and nitrite accumulation tests showed that PHBV and its bionanocomposites were biocompatible.