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Novel area-selective molecular layer deposition (AS-MLD) of polyimide (PI) on Cu versus native SiO2 was studied. By use of 1,6-diaminohexane (DAH) and pyromellitic dianhydride (PMDA) as precursors, PI films can be selectively deposited on the Cu surface at 200-210 degrees C with a rate around 7.8 A/cycle while negligible growth takes place on SiO2. The selectivity was successfully demonstrated also on Cu/SiO2 patterns at 200 degrees C; after 180 MLD cycles, around 140 nm thick PI was deposited on Cu regions while

Reversible addition-fragmentation chain transfer (RAFT) dispersion polymerisation in supercritical carbon dioxide is an effective process for creating block copolymer microparticles with internal nanostructures. Here we report an alternative synthesis route involving completely independent steps by exploiting the livingness of RAFT-terminated PMMA microparticles and their unique ability to be redispersed in scCO(2). This not only enables a series of block copolymers to be created from a single RAFT dispersion synthesised PMMA homopolymer batch, thus improving reproducibility, but also adds flexibility by allowing the time and concentration requirements for each stage to be decoupled. The internal morphology development and evolution for a series of poly(methyl methacrylate-block-styrene) (PMMA-b-PS) block copolymer microparticles synthesised via this route was monitored via in situ small-angle X-ray scattering (SAXS) using an autoclave with diamond windows. Together with offline kinetics experiments and postmortem transmission electron microscopy imaging, this study provides remarkably detailed insights into block copolymer self-organisation phenomena in scCO(2). Specifically, the time period over which this block copolymer undergoes phase separation before progressing from an arrangement of spheres to lamellae via the hexagonal cylinder phase is elucidated, and the data are used to plot a detailed empirical phase diagram for this block copolymer system in scCO(2).

We report on the role of temperature and shear on the melt behavior of iPP in the presence of the organic compound N1,N1′-(propane-1,3-diyl)bis(N2-hexyloxalamide) (OXA3,6). It is demonstrated that OXA3,6 facilitates a viscosity suppression when it resides in the molten state. The viscosity suppression is attributed to the interaction of iPP chains/subchains with molten OXA3,6 nanoclusters. The exact molecular mechanism has not been identified; nevertheless, a tentative explanation is proposed. The observed viscosity suppression appears similar to that encountered in polymer melts filled with solid nanoparticles, with the difference that the OXA3,6 compound reported in this study facilitates the viscosity suppression in the molten state. Upon cooling, as crystal growth of OXA3,6 progresses, the decrease in viscosity is suppressed. Retrospectively, segmental absorption of iPP chains on the surface of micrometer-sized OXA3,6 crystallites favors the formation of dangling arms, yielding OXA3,6 crystallites decorated with partially absorbed iPP chains. In other words, the resulting OXA3,6 particle morphology resembles that of a hairy particle or a starlike polymer chain. Such hairy particles effectively facilitate a viscosity enhancement, similar to branched polymer chains. This hypothesis and its implications for the shear behavior of iPP are discussed and supported using plate-plate rheometry and slit-flow experiments combined with small-angle X-ray scattering analysis.

Ultrabright x-rays capture the sequence of material damage accumulation during high strain rate catastrophic failure., Understanding high-velocity impact, and the subsequent high strain rate material deformation and potential catastrophic failure, is of critical importance across a range of scientific and engineering disciplines that include astrophysics, materials science, and aerospace engineering. The deformation and failure mechanisms are not thoroughly understood, given the challenges of experimentally quantifying material evolution at extremely short time scales. Here, copper foils are rapidly strained via picosecond laser ablation and probed in situ with femtosecond x-ray free electron (XFEL) pulses. Small-angle x-ray scattering (SAXS) monitors the void distribution evolution, while wide-angle scattering (WAXS) simultaneously determines the strain evolution. The ability to quantifiably characterize the nanoscale during high strain rate failure with ultrafast SAXS, complementing WAXS, represents a broadening in the range of science that can be performed with XFEL. It is shown that ultimate failure occurs via void nucleation, growth, and coalescence, and the data agree well with molecular dynamics simulations.

The increasing interest in atomic layer deposition (ALD) of Pt for the controlled synthesis of supported nanoparticles for catalysis demands an in-depth understanding of the nucleation controlled growth behaviour. We present an in situ investigation of Pt ALD on planar Si substrates, with native SiO2, by means of X-ray fluorescence (XRF) and grazing incidence small-angle X-ray scattering (GISAXS), using a custom-built synchrotron-compatible high-vacuum ALD setup and focusing on the thermal Pt ALD process, comprising (methylcyclopentadienyl)trimethylplatinum (MeCpPtMe3) and O-2 gas at 300 degrees C. The evolution in key scattering features provides insights into the growth kinetics of Pt deposits from small nuclei to isolated islands and coalesced worm-like structures. An analysis approach is introduced to extract dynamic information on the average real space parameters, such as Pt cluster shape, size, and spacing. The results indicate a nucleation stage, followed by a diffusion-mediated particle growth regime that is marked by a decrease in average areal density and the formation of laterally elongated Pt clusters. Growth of the Pt nanoparticles is thus not only governed by the adsorption of Pt precursor molecules from the gas-phase and subsequent combustion of the ligands, but is largely determined by adsorption of migrating Pt species on the surface and diffusion-driven particle coalescence. Moreover, the influence of the Pt precursor dose on the particle nucleation and growth is investigated. It is found that the precursor dose influences the deposition rate (number of Pt atoms per cycle), while the particle morphology for a specific Pt loading is independent of the precursor dose used in the ALD process. Our results prove that combining in situ GISAXS and XRF provides an excellent experimental strategy to obtain new fundamental insights about the role of deposition parameters on the morphology of Pt ALD depositions. This knowledge is vital to improve control over the Pt nucleation stage and enable efficient synthesis of supported nanocatalysts.

The out-of-equilibrium dynamics of electrons and phonons upon laser excitation are often described by the two-temperature model, which assumes that both subsystems are separately in thermal equilibrium. However, recent experiments show that this description is not sufficient to describe the out-of-equilibrium dynamics on ultrashort timescales. Here, we extend and apply a parameter-free microscopic out-of-equilibrium model to describe the ultrafast laser-induced system dynamics of archetypical metallic systems such as gold, aluminum, iron, nickel, and cobalt. We report strong deviations from the two-temperature model on the picosecond timescale for all the materials studied, even for those where the assumption of separate thermal equilibriums seemed less restrictive, like in gold. Furthermore, we demonstrate the importance of the phonon-mode dependent electron-phonon coupling for the relaxation process and reveal the significance of this channel in the lattice equilibration through an indirect coupling between phonons via the electronic system.

The interaction between cellulose and hemicelluloses is of fundamental importance for understanding the molecular architecture of plant cell walls. Adsorption of xyloglucan (XG) onto regenerated cellulose (RC), sulfated cellulose nanocrystal (s-CNC), and desulfated cellulose nanocrystal (d-CNC) films was studied by quartz crystal microbalance with dissipation monitoring, surface plasmon resonance, and atomic force microscopy. The amount of XG adsorbed onto different cellulose substrates increased in the order RC < s-CNC < d-CNC. The adsorption of XG onto RC films was independent of film thickness (d), whereas XG adsorption was weakly dependent on d for s-CNC films and strongly dependent on d for d-CNC films. However, approximately the same amount of XG adsorbed onto “monolayer-thin” films of RC, s-CNC, and d-CNC. These results suggest that the morphology and surface charge of the cellulose substrate played a limited role in XG adsorption and highlight the importance of film thickness of cellulose nanocrystalline films to XG adsorption.

International audience; We report on the effect of an aliphatic oxalamide based nucleating agent (OXA3,6) on the melt and crystallization behavior of isotactic polypropylene (iPP) under defined shear conditions. Through polarized optical microscopy, we demonstrate that OXA3,6 self-assembles from the iPP melt into rhombic crystals whereas their size and distribution proved highly dependent on the employed cooling rates. The presence of 0.5 wt % of OXA3,6 in iPP results in a significant suppression in iPP melt viscosity, which could not be explained via molecular modeling. A possible cause for the drop in viscosity in the presence of OXA3,6 is attributed to the interaction (absorption) of high molecular weight iPP chains with the nucleating agent, thereby suppressing their contribution to the viscoelastic response of the melt. This proposed mechanism for the suppression in melt viscosity appears similar to that encountered by the homogeneous distribution of nanoparticles such as CNTs, graphene, and silica. Shear experiments, performed using a slit flow device combined with small- angle X-ray diffraction measurements, indicate that crystallization is significantly enhanced in the presence of OXA3,6 at relatively low shear rates despite its lowered sensitivity to shear. This enhancement in crystallization is attributed to the shear alignment of the rhombic OXA3,6 crystals that provide surface for iPP kebab growth upon cooling. Overall, the suppression in melt viscosity in combination with enhanced nucleation efficiency at low as well as high shear rates makes this self-assembling oxalamide based nucleating agent a promising candidate for fast processing.

The combination of asymmetric P4VP-b-PAPI diblock copolymers (i.e. f P 4 VP ≠ f PAPI ) and 3-NDP surfactants in hydrogen-bonded [poly(4-vinylpyridine)-block-poly(N-acryloylpiperidine)](3-nonadecylphenol)x (P4PA(3-NDP)x) supramolecular double-comb diblock copolymers could potentially result in rather interesting morphologies. However, plasticization of the copolymer and the ability of 3-NDP to crystallize were found to affect their self-assembly significantly. In general, for high comb densities x, the complex's tendency to crystallize and its preference to form a flat interface dominated microphase separation. Lower values of x on the other hand gave uneven distribution of 3-NDP, resulting in a higher glass transition temperature of the P4VP block. Crystallization of 3-NDP's aliphatic tails was therefore in most cases restricted to the preferential PAPI microdomains, thereby maintaining the large length scale block copolymer morphology that was already present in the melt. Such behavior is identical to self-assembly of linear semicrystalline diblock copolymers, as in these type of systems structure formation depends on the segregation strength and relative magnitude of the order-disorder transition ( T ODT ), T g and T c , leading to mechanisms like confined crystallization or breakout.

Herein, we elucidate the impact of tubular confinement on the structure and relaxation behavior of poly(vinylidene difluoride) (PVDF) and how these affect the para-/ferroelectric behavior of this polymer. We use PVDF nanotubes that were solidified in anodic aluminum oxide (AAO) templates. Dielectric spectroscopy measurements evidence a bimodal relaxation process for PVDF nanotubes: besides the bulk-like α-relaxation, we detect a notably slower relaxation that is associated with the PVDF regions of restricted dynamics at the interface with the AAO pore. Strikingly, both the bulk-like and the interfacial relaxation tend to become temperature independent as the temperature increases, a behavior that has been observed before in inorganic relaxor ferroelectrics. In line with this, we observe that the real part of the dielectric permittivity of the PVDF nanotubes exhibits a broad maximum when plotted against the temperature, which is, again, a typical feature of relaxor ferroelectrics. As such, we propose that, in nanotubular PVDF, ferroelectric-like nanodomains are formed in the amorphous phase regions adjacent to the AAO interface. These ferroelectric nanodomains may result from an anisotropic chain conformation and a preferred orientation of local dipoles due to selective H-bond formation between the PVDF macromolecues and the AAO walls. Such relaxor-ferroelectric-like behavior has not been observed for nonirradiated PVDF homopolymer; our findings thus may enable in the future alternative applications for this bulk commodity plastic, e.g., for the production of electrocaloric devices for solid-state refrigeration which benefit from a relaxor-ferroelectric-like response., J.M. acknowledges support from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant, agreement No. 654682. A.A. and A.I. acknowledge financial support from the Spanish Ministry Ministerio de Economia y Competitividad (MINECO) (code: MAT2015-63704-P (MINECO/FEDER, UE)) and the Eusko Jaurlaritza (Basque Government) (code: IT-654-13). A.C. would like to acknowledge the financial support of the EPSRC (EP/M014142/1). A.N., T.A.E., and C.M. acknowledge financial support from MINECO (codes: MAT2014-59187-R, MAT2015-66443-C02-1-R, and MAT2014-53437-C2-1P, respectively). N.S. is in addition grateful for support from a European Research Council ERC Starting Independent Research Fellowship under the grant agreement No. 279587.

In this work we followed the formation of palladium nanoparticles, starting from palladium (II) acetate precursor, inside a poly(4-vinylpyridine-co-divinylbenzene) polymer in presence of different reducing agents. The formation and growth of palladium nanoparticles in presence of H-2 was followed as a function of temperature by simultaneous XANES-SAXS techniques, coupled with DRIFT spectroscopy in operando conditions. It was found that the pyridyl functional groups in the polymer plays a fundamental role in the stabilization of the palladium (II) acetate precursor, as well as in the stabilization of the palladium nanoparticles. The effect of a thermal treatment in alcohol (ethanol and 2-propanol) was preliminarily investigated by means of DRIFT spectroscopy in operando conditions. We found that alcohols act as reducing agents for Pd(OAc)(2). The obtained palladium nanoparticles were preliminarily characterized by means of IR spectroscopy using CO as probe molecule. (C) 2016 Elsevier B.V. All rights reserved.

In solution-processed organic bulk heterojunction (BHJ) solar cells, the purity of the phase-separated domains is known to play an important role in determining device function. While the effects of domain purity have been investigated by tuning of the BHJ morphology, such tuning typically results in several parameters (for example domain size and crystallinity) being varied at once. Here we show that by varying the time between spin-coating and the application of an anti-solvent treatment, the domain purity of the polymer-rich phase in PBDTTT-EFT: PC71BM blends can be tuned while keeping other morphological parameters constant. This unique approach enables the effect of domain purity on device function to be isolated and quantified. Over the purity range explored, solar cell power conversion efficiency is observed to monotonically increase from 7.2% to 9.6% with increasing domain purity, with the cell fill factor most affected by changes in domain purity. Employing transient photovoltage measurements we find that purer phases result in a reduction in the rate constant of bimolecular recombination. A more thorough treatment is also presented on the relationship between the total scattering intensity (derived from resonant soft X-ray scattering measurements) and domain purity. In particular it is shown that domain purity does not scale linearly with total scattering intensity requiring an initial estimate of absolute domain composition.

The ability to control crystallization reactions is required in a vast range of processes including the production of functional inorganic materials and pharmaceuticals and the prevention of scale. However, it is currently limited by a lack of understanding of the mechanisms underlying crystal nucleation and growth. To address this challenge, it is necessary to carry out crystallization reactions in well-defined environments, and ideally to perform in situ measurements. Here, a versatile microfluidic synchrotron-based technique is presented to meet these demands. Droplet microfluidic-coupled X-ray diffraction (DMC-XRD) enables the collection of time-resolved, serial diffraction patterns from a stream of flowing droplets containing growing crystals. The droplets offer reproducible reaction environments, and radiation damage is effectively eliminated by the short residence time of each droplet in the beam. DMC-XRD is then used to identify effective particulate nucleating agents for calcium carbonate and to study their influence on the crystallization pathway. Bioactive glasses and a model material for mineral dust are shown to significantly lower the induction time, highlighting the importance of both surface chemistry and topography on the nucleating efficiency of a surface. This technology is also extremely versatile, and could be used to study dynamic reactions with a wide range of synchrotron-based techniques.

Understanding and controlling the electronic structure of thin layers of quantum materials is a crucial first step towards designing heterostructures where new phases and phenomena, including the metal-insulator transition (MIT), emerge. Here, we demonstrate control of the MIT via tuning electronic bandwidth and local site environment through selection of the number of atomic layers deposited. We take CaVO3, a correlated metal in its bulk form that has only a single electron in its V4+ 3d manifold, as a representative example. We find that thick films and ultrathin films (≤6 unit cells, u.c.) are metallic and insulating, respectively, while a 10 u.c. CaVO3 film exhibits a clear thermal MIT. Our combined X-ray absorption spectroscopy and resonant inelastic X-ray scattering (RIXS) study reveals that the thickness-induced MIT is triggered by electronic bandwidth reduction and local moment formation from V3+ ions, that are both a consequence of the thickness confinement. The thermal MIT in our 10 u.c. CaVO3 film exhibits similar changes in the RIXS response to that of the thickness-induced MIT in terms of reduction of bandwidth and V 3d–O 2p hybridization., npj Quantum Materials, 4 (1), ISSN:2397-4648

Scanning tunneling microscopy, low-energy electron diffraction, and helium atom scattering show a transition to a dimerizationlike reconstruction in the one-dimensional atomic chains on Bi(114) at low temperatures. One-dimensional metals are generally unstable against such a Peierls-like distortion, but neither the shape nor the spin texture of the Bi(114) Fermi contour favors the transition: Although the Fermi contour is one dimensional and thus perfectly nested, the very short nesting vector $2{k}_{F}$ is inconsistent with the periodicity of the distortion. Moreover, the nesting occurs between two Fermi contour branches of opposite spin, which is also expected to prevent the formation of a Peierls phase. Indeed, angle-resolved photoemission spectroscopy does not reveal any change in the electronic structure near the Fermi energy around the phase transition. On the other hand, distinct changes at higher binding energies are found to accompany the structural phase transition. This suggests that the transition of a strong-coupling type and that it is driven by phonon entropy rather than electronic entropy. This picture is supported by the observed short correlation length of the pairing distortion, the second-order-like character of the phase transition, and pronounced differences between the surface phonon spectra of the high- and low-temperature phases.

Knowledge of the transitions occurring during the formation of ion-conducting polymer films and membranes is crucial to optimize material performances. The use of non-destructive scattering techniques that offer high spatio-temporal resolution is essential to investigating such structural transitions, especially when combined with complementary techniques probing at different time and spatial scales. Here, a simultaneous multi-technique study is performed on the membrane formation mechanism and the subsequent hydration of two ion-conducting polymers, the well-known commercial Nafion and a synthesized sulfonated poly(phenylene sulfide sulfone) (sPSS). The X-ray data distinguish the multi-stage processes occurring during drying. A sol-gel-membrane transition sequence is observed for both polymers. However, while Nafion membrane evolves from a micellar solution through the formation of a phase-separated gel, forming an oriented supported membrane, sPSS membrane evolves from a solution of dispersed polyelectrolyte chains via formation of an inhomogeneous gel, showing assembly and ionic phase separation only at the end of the drying process. Impedance spectroscopy data confirm the occurrence of the sol-gel transitions, while gel-membrane transitions are detected by optical reflectance data. The simultaneous multi-technique approach presented here can connect the nanoscale to the macroscopic behavior, unraveling information essential to optimize membrane formation of different ion-conducting polymers.

The zinc-substituted polyoxotungstate [PW11Zn(H2O)O-39](5-) (PW11Zn) has been encapsulated within the aluminium(III) 2-aminoterephthalate NH2-MIL-101(Al) metal-organic framework (MOF) either directly through a one-pot microwave-assisted synthesis or by an impregnation method. The resultant composite materials were characterized by elemental analysis, powder X-ray diffraction, FTIR spectroscopy, and P-31 magic-angle spinning (MAS) NMR spectroscopy. The desulfurization of a model diesel containing three refractory organosulfur compounds (1-benzothiophene, dibenzothiophene, and 4,6-dimethyldibenzothiophene) was studied with the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate as an extractant, the PW11Zn@MOF composites as sulfoxidation catalysts, and aqueous H2O2 as an oxidant. The composite obtained by direct synthesis was the most efficient catalyst and led to almost complete desulfurization of the model diesel under mild conditions. Moreover, the solid catalyst could be recovered readily and recycled without significant loss of desulfurization performance. The application of this system to the treatment of a real diesel sample provided a very good sulfur removal of 83% when combined with liquid-liquid extraction.

The developments in synchrotron radiation based polymer research have been profound over the last two decades. Not only have many more beamlines suitable for soft condensed matter research become available since the pioneering days but also the technical developments with respect to X-ray beam quality and position sensitive X-ray detectors have been very substantial. This has allowed to increase the degree of experimental sophistication considerably by introducing sample environments which not only allow the materials to be studied outside of equilibrium conditions but in fact in conditions which closely start to resemble realistic processing conditions. These developments now allow polymer researchers to bring synchrotron radiation based tools to the whole spectrum from academic relevant characterisations to trying to understand the effects that desired processing parameters have on the final materials.In this manuscript, which is not intended as a comprehensive history, it is described how the historic interplay between technical developments and the experimental desires has generated the soft condensed matter synchrotron radiation toolbox that is at present available by following some of the major areas that have been the subject of polymers in the last two decades. (C) 2016 Elsevier Ltd. All rights reserved.

This study reports a detailed characterization of the phase transition behavior and polymorphism of fatty alcohols with different chain lengths in peanut oil. Upon crystallization, fatty alcohols nucleated into rotator phases, which then transformed into well-defined crystal polymorphs. At concentrations greater than 30%, fatty alcohol crystals were in the monoclinic γ-form with a lamellar thickness that decreased as the length of the carbon chain of the fatty alcohols decreased. At concentrations lower than 30%, on the other hand, fatty alcohol crystals formed an orthorhombic β′-form. In this case, two main crystal families with lamellar thicknesses were detected. In particular, the thicker family range was from 5.95 to 4.96 nm moving from 1-docosanol to 1-hexadecanol while the thinner family range was from 4.98 to 3.68 nm. The thicker crystal population progressively decreased, while the thinner crystal population increased, suggesting an interconversion between these species. The kinetics of these chan...

Two PDMS-SiO2-TiO2-Cao porous hybrid materials were prepared using the same base composition, precursors, and solvents, but following two different sol-gel procedures, based on the authors' previous works where for the first time, in this hybrid system, calcium acetate was used as calcium source. The two different procedures resulted in monolithic materials with different structures, microstructures, and surface wettability. Even though both are highly hydrophobic (contact angles of 127.2 degrees and 150.6 degrees), and present different filling regimes due to different surface topographies, they have demonstrated to be-cytocompatible when tested with human osteoblastic cells, against the accepted idea that high-hydrophobic surfaces are not suitable to cell adhesion and proliferation. At the nanoscale, the existence of hydrophilic silica domains containing calcium, where water molecules are physisorbed, is assumed to support this capability, as discussed. (C) 2016 Elsevier B.V. All rights reserved.

The mesoscopic morphology of mixtures of ethylammonium nitrate, a protic ionic liquid, and n-pentanol is explored for the first time using small angle X-ray scattering as a function of concentration and temperature. Both compounds are amphiphilic and characterized by an extended hydrogen bonding network; however, though macroscopically homogeneous, their mixtures are highly heterogeneous at the mesoscopic spatial scales. Previous structural studies rationalized similar features in related mixtures proposing the existence of large aggregates or micelle- and/or microemulsion-like structures. Here we show that a detailed analysis of the present concentration and temperature resolved experimental data set supports a structural scenario where the mesoscopic heterogeneities are the due to density fluctuations that are precursors of liquid-liquid phase separation. Accordingly no existence of structurally organized aggregates (such as micellar or microemulsion aggregates) is required to account for the mesoscopic heterogeneities detected in this class of binary mixtures.

We investigate the effect of microfluidic flow on the microstructure and dynamics of a model surfactant mixture, combining synchrotron Small Angle X-ray Scattering (SAXS), microscopy and rheology. A system comprising a single-chain cationic surfactant, hexadecyl trimethyl ammonium chloride (C16TAC), a short-chain alcohol (1-pentanol) and water was selected for the study due to its flow responsiveness and industrial relevance. Model flow fields, including sequential contraction-expansion (extensional) and rotational flows, were investigated and the fluid response in terms of the lamellar d-spacing, orientation and birefringence was monitored in situ, as well as the recovery processes after cessation of flow. Extensional flows are found to result in considerable d-spacing increase (from approx 59 Å to 65 Å). However, under continuous flow, swelling decreases with increasing flow velocity, eventually approaching the equilibrium values at velocities ≃2 cm s(-1). Through individual constrictions we observe the alignment of lamellae along the flow velocity, accompanied by increasing birefringence, followed by an orientation flip whereby lamellae exit perpendicularly to the flow direction. The resulting microstructures are mapped quantitatively onto the flow field in 2D with 200 μm spatial resolution. Rotational flows alone do not result in appreciable changes in lamellar spacing and flow type and magnitude evidently impact the fluid microstructure under flow, as well as upon relaxation. The findings are correlated with rheological properties measured ex situ to provide a mechanistic understanding of the effect of flow imposed by tubular processing units in the phase behavior and performance of a model surfactant system with ubiquitous applications in personal care and coating industries.

Predicting strains, stresses and swelling in nuclear power plant components exposed to irradiation directly from the observed or computed defect and dislocation microstructure is a fundamental problem of fusion power plant design that has so far eluded a practical solution. We develop a model, free from parameters not accessible to direct evaluation or observation, that is able to provide estimates for irradiation-induced stresses and strains on a macroscopic scale, using information about the distribution of radiation defects produced by high-energy neutrons in the microstructure of materials. The model exploits the fact that elasticity equations involve no characteristic spatial scale, and hence admit a mathematical treatment that is an extension to that developed for the evaluation of elastic fields of defects on the nanoscale. In the analysis given below we use, as input, the radiation defect structure data derived from ab initio density functional calculations and large-scale molecular dynamics simulations of high-energy collision cascades. We show that strains, stresses and swelling can be evaluated using either integral equations, where the source function is given by the density of relaxation volumes of defects, or they can be computed from heterogeneous partial differential equations for the components of the stress tensor, where the density of body forces is proportional to the gradient of the density of relaxation volumes of defects. We perform a case study where strains and stresses are evaluated analytically and exactly, and develop a general finite element method implementation of the method, applicable to a broad range of predictive simulations of strains and stresses induced by irradiation in materials and components of any geometry in fission or fusion nuclear power plants.

Treatment of polymicrobial infections requires combination therapy with drugs that have different antimicrobial spectra and possibly work in synergy. However, the different pharmacokinetics and adverse side effects challenge the simultaneous delivery of multiple drugs at the appropriate concentrations to the site of infection. Formulation of multiple drugs in nano-carrier systems may improve therapeutic efficacy by increasing the local concentration and lowering the systemic concentration, leading to fewer side effects. In this study, we loaded polymyxin B and vancomycin on bare and carboxyl-modified mesoporous silica nanoparticles (B-MSNs and C-MSNs, respectively) to achieve simulataneous local delivery of antibiotics against Gram-positive and –negative bacteria. Polymyxin B adsorbed preferentially to nanoparticles compared to vancomycin. The total antibiotic loading was 563 μg and 453 μg per mg B-MSNs or C-MSNs, respectively. Both B-MSNs and C-MSNs loaded with antibiotics were effective against Gram-negative and Gram-positive bacteria. The antibiotics had synergistic interactions against Gram-negative bacteria, and the antimicrobial efficacy was higher for antibiotic-loaded C-MSNs compared to free antibiotics at the same concentration even though the cytotoxicity was lower. Our study shows that formulations of existing antibiotics in nanocarrier systems can improve their therapeutic efficiency, indicating that combination therapy with drug-loaded silica nanoparticles may provide a better treatment outcome for infections that require high concentrations of multiple drugs.

Bioconjugates established between anionic polyethylene glycol (PEG) based polymers and cationic proteins have proven to be a promising strategy to engineer thermostable biocatalysts. However, the enzyme activity of these bioconjugates is very low and the mechanism of non-covalent PEG-stabilization is yet to be understood. This work presents experimental and molecular dynamics simulation studies, using lipase-polymer surfactant nanoconjugates from mesophile Rhizomucor miehei (RML), performed to evaluate the effect of PEG on enzyme stability and activity. Results demonstrated that the number of hydrogen bonds between the cationized RML and PEG chain correlates with enzyme thermostability. In addition, an increase of both the number of PEG-polymers units and cationization degree of the enzyme leads to a decrease of enzyme activity. Modelling with SAXS data of aqueous solutions of the biofluid lipases agrees with previous hypothesis that these enzymes contain a core constituted of folded protein confined by a shell of surfactants. Together results provide valuable insight into the mechanism of non-covalent PEG mediated protein stabilization relevant for engineering active and thermostable biofluids. Furthermore, the first biofluids RML with activity comparable to their cationized counterpart are presented.

In this work small-angle X-ray scattering (SAXS) was used to study hydration and temperature-induced changes of pig gastric mucin (PGM) within the entire concentration range. The scattering is interpreted as originating from PGM fiber-like structures that adopt rod-like bottle-brush conformation in dilute solutions. On the basis of the knowledge about molecular structure of mucins and SAXS data for dilute solutions, we propose a theoretical model for predicting mucin conformation in solution and calculate the corresponding scattering profile. This bottle-brush model comprises a protein backbone with carbohydrate side chains and corresponding structural parameters, such as grafting distance and lengths of the backbone and side chains. It describes the experimental PGM data from dilute solutions in the full q range very well. It furthermore suggests that the carbohydrate side chains are grafted with a regular separation of around 5 nm and a length of 14 nm. The cross-section size with a radius of about 1 nm is also in accordance with the size of the carbohydrate units. Structuring of PGM solutions at higher concentrations was investigated by analyzing semidilute and concentrated PGM samples. Starting at about 20 wt %, Bragg peaks become clearly visible indicating a more ordered mucin system. In very dehydrated and fully dry mucin samples these peaks are not present indicating lack of long-range order. The SAXS data show that the structural change occurring at about 80 wt % mucin and 25 degrees C corresponds to a glass transition in agreement with our previous calorimetric results. Temperature also has an effect on the phase behavior of mucin. At intermediate levels of hydration, a phase transition is observed at about 60-70 degrees C. The main Bragg peak appears to split in two, indicating formation of a different structure at elevated temperatures. These findings are used to improve the PGM water phase diagram.

The coupling of droplet microfluidics and Small Angle Neutron Scattering (SANS) is demonstrated with a range of model systems: isotopic solvent (H2O/D2O) mixtures, surfactant (sodium dodecyl sulfate, SDS) solutions and colloidal (silica) suspensions. Several droplet carrier phases are evaluated and fluorinated oil emerges as a suitable fluid with minimal neutron background scattering (commensurate with air), and excellent interfacial properties. The combined effects of flow dispersion and compositional averaging caused by the neutron beam footprint are evaluated in both continuous and droplet flows and an operational window is established. Systematic droplet-SANS dilution measurements of colloidal silica suspensions enable unprecedented quantification of form and structure factors, osmotic compressibility, enhanced by constrained global data fits. Contrast variation measurements with over 100 data points are readily carried out in 10-20 min timescales, and validated for colloidal silica of two sizes, in both continuous and droplet flows. While droplet microfluidics is established as an attractive platform for SANS, the compositional averaging imposed by large (∼1 cm) beam footprints can, under certain circumstances, make single phase, continuous flow a preferable option for low scattering systems. We propose simple guidelines to assess the suitability of either approach based on well-defined system parameters.

The annealing behavior of very thin SiO2/Ge multilayers deposited on Si substrate by e-gun deposition in high vacuum was explored. It is shown that, after annealing at moderate temperatures (800°C) in inert atmosphere, Ge is completely outdiffused from the SiO2 matrix leaving small (about 3 nm) spherical voids embedded in the SiO2 matrix. These voids are very well correlated and formed at distances governed by the preexisting multilayer structure (in vertical direction) and self-organization (in horizontal direction). The formed films produce intensive photoluminescence (PL) with a peak at 500 nm. The explored dynamics of the PL decay show the existence of a very rapid process similar to the one found at Ge/SiO2 defected interface layers.

While the surface atomic structure of RuO2 has been well studied in ultra high vacuum, much less is known about the interaction between water and RuO2 in aqueous solution. In this work, in situ surface X-ray scattering measurements combined with density functional theory (DFT) were used to determine the surface structural changes on single-crystal RuO2(110) as a function of potential in acidic electrolyte. The redox peaks at 0.7, 1.1 and 1.4 V vs. reversible hydrogen electrode (RHE) could be attributed to surface transitions associated with the successive deprotonation of -H2O on the coordinatively unsaturated Ru sites (CUS) and hydrogen adsorbed to the bridging oxygen sites. At potentials relevant to the oxygen evolution reaction (OER), an -OO species on the Ru CUS sites was detected, which was stabilized by a neighboring -OH group on the Ru CUS or bridge site. Combining potential-dependent surface structures with their energetics from DFT led to a new OER pathway, where the deprotonation of the -OH group used to stabilize -OO was found to be rate-limiting., Skoltech-MIT Center for Electrochemical Energy (Agreement 02/MI/MIT/CP/11/07633/GEN/G/00), National Science Foundation (U.S.) (Grant ACI-1548562)

Mixed micelle formation between two oppositely charged diblock copolymers that have a common thermosensitive nonionic block of poly(N-isopropylacrylamide) (PNIPAAM) has been studied. The block copolymer mixed solutions were investigated under equimolar charge conditions as a function of both temperature and total polymer concentrations by turbidimetry, differential scanning calorimetry, two-dimensional proton nuclear magnetic nuclear Overhauser effect spectroscopy (2D H-1 NMR NOESY), dynamic light scattering, and small angle X-ray scattering measurements. Well-defined and electroneutral cylindrical micelles were formed with a radius and a length of about 3 nm and 35 nm, respectively. In the micelles, the charged blocks built up a core, which was surrounded by a corona of PNIPAAM chains. The 2D H-1 NMR NOESY experiments showed that a minor block mixing occurred between the core blocks and the PNIPAAM blocks. By approaching the lower critical solution temperature of PNIPAAM, the PNIPAAM chains collapsed, which induced aggregation of the micelles. (c) 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 1457-1469

Thermotropic smectic liquid crystalline polymers were used as a scaffold to create organic/inorganic hybrid layered nanomaterials. Different polymers were prepared by photopolymerizing blends of a hydrogen bonded carboxylic acid derivative and a 10 % cross-linker of variable length in their liquid crystalline phase. Nanopores with dimensions close to 1 nm were generated by breaking the hydrogen bonded dimers in a high pH solution. The pores were filled with positively charged silver (Ag) ions, resulting in a layered silver(I)-polymeric hybrid material. Subsequent exposure to a NaBH4 reducing solution allowed for the formation of supported hybrid metal/organic films. In the bulk of the film the dimension of the Ag nanoparticles (NPs) was regulated with subnanometer precision by the cross-linker length. Ag nanoparticles with an average size of 0.9, 1.3, and 1.8 nm were produced inside the nanopores thanks to the combined effect of spatially confined reduction and stabilization of the nanoparticles by the polymer carboxylic groups. At the same time, strong Ag migration occurred in the surface region, resulting in the formation of a nanostructured metallic top layer composed of large (10–20 nm) NPs.

The mechanism of Pt and PtPb nanocrystal formation under supercritical ethanol conditions has been investigated by means of in situ X-ray total scattering and pair distribution function (PDF) analysis. The metal complex structures of two different platinum precursor solutions, chloroplatinic acid and Pt(acac)(2) (acac=acetylacetonate) provide atomic-scale detail about the nucleation mechanisms after initiation of the reaction with Pb(acac)(2) by heating. The stronger Pt-O chemical bonding in the Pt(acac)(2) precursor complex compared with the Pt-Cl bonding in the chloroplatinic acid precursor complex leads to a much slower reduction of the Pt center, and this allows more optimal co-reduction conditions providing a pathway for formation of phase-pure intermetallic PtPb product. The matching chemistry of the Pt(acac)(2) and Pb(acac)(2) precursors allow development of a facile continuous flow supercritical ethanol process for obtaining phase-pure hexagonal PtPb nanocrystals. The study thus highlights the importance of in situ studies in revealing atomic-scale information about nucleation mechanisms, which can be used in design of specific synthesis pathways, and the new continuous-flow process to obtain PtPb nanocrystals holds potential for large-scale production.

International audience; The directed self-assembly of diblock copolymer chains (poly(1,1-dimethylsilacyclobutane)-block-polystyrene, PDMSB-b-PS) into a thin film double gyroid structure is described. A decrease of the kinetics of a typical double-wave pattern formation is reported within the 3D-nanostructure when the film thickness on mesas is lower than the gyroid unit cell. However, optimization of the solvent-vapor annealing process results in very large grains (over 10 μm²) with specific orientation (i.e., parallel to the air substrate) and direction (i.e., along the groove direction) of the characteristic (211) plane, demonstrated by templating sub-100-nm-thick PDMSB-b-PS films.

We report a microfluidic approach to perform small angle neutron scattering (SANS) measurements of contrast variation and matching, extensively employed in soft and biological matter research. We integrate a low scattering background microfluidic mixer and serpentine channel in a SANS beamline to yield a single phase, continuous flow, reconfigurable liquid cell. By contrast with conventional, sequential measurements of discrete (typically 4-6) solutions of varying isotopic solvent composition, our approach continually varies solution composition during SANS acquisition. We experimentally and computationally determine the effects of flow dispersion and neutron beam overillumination of microchannels in terms of the composition resolution and precision. The approach is demonstrated with model systems: H2O/D2O mixtures, a surfactant (sodium dodecyl sulfate, SDS), a triblock copolymer (pluronic F127), and silica nanoparticles (Ludox) in isotopic aqueous mixtures. The system is able to zoom into a composition window to refine contrast matching conditions, and robustly resolve solute structure and form factors by simultaneous fitting of scattering data with continuously varying contrast. We conclude by benchmarking our microflow-SANS with the discrete approach, in terms of volume required, composition resolution and (preparation and measurement) time required, proposing a leap forward in equilibrium, liquid solution phase mapping and contrast variation by SANS.

The morphological evolution of cylinder-forming poly(styrene)-b-poly(methyl methacrylate) block copolymer (BCP) thick films treated at high temperatures in the rapid thermal processing (RTP) machine was monitored by means of in-depth grazing-incidence small-angle X-ray scattering (GISAXS). The use of this nondisruptive technique allowed one to reveal the formation of buried layers composed of both parallel-and perpendicular-oriented cylinders as a function of the film thickness (24 700 nm, the two interfaces are completely decoupled, and the formation of a superficial layer of about 50 nm composed of perpendicular cylinders is observed. Furthermore, the through-film morphology affects the nanodomain long-range order, which substantially decreases in correspondence with the beginning of the decoupling process. When the thick samples are exposed to longer thermal treatments, an increase in the long-range order of the nanodomains occurs, without any sensible variation of the thickness of the superficial layer.

Small angle X-ray and neutron scattering (SAXS/SANS) provide a non-localised quantitative analysis of nanoscale ω precipitates in Ti-7Mo at.% and Gum metal, a Ti-Nb based alloy. The nucleation and coarsening kinetics are more rapid in the Ti-Nb alloy than the Ti-Mo alloy, presumably as Nb diffuses more rapidly than Mo in Ti. Therefore Mo-based β -Ti alloys are more stable during ω ageing than Nb-based β -Ti alloys. To the authors’ knowledge, this represents the first publication quantifying ω size, volume fraction and element partitioning in Gum metal.

The formation of ionic liquid (IL) mixtures has been proposed as an approach to rationally fine-tune the physicochemical properties of ILs for a variety of applications. However, the effects of forming such mixtures on the resultant properties of the liquids are only beginning to be understood. Towards a more complete understanding of both the thermodynamics of mixing ILs and the effect of mixing these liquids on their structures and physicochemical properties, the spatial arrangement and free volume of IL mixtures containing the common [C4C1im]+ cation and different anions have been systematically explored using small angle X-ray scattering (SAXS), positron annihilation lifetime spectroscopy (PALS) and 129Xe NMR techniques. Anion size has the greatest effect on the spatial arrangement of the ILs and their mixtures in terms of the size of the non-polar domains and inter-ion distances. It was found that differences in coulombic attraction between oppositely charged ions arising from the distribution of charge density amongst the atoms of the anion also significantly influences these inter-ion distances. PALS and 129Xe NMR results pertaining to the free volume of these mixtures were found to strongly correlate with each other despite the vastly different timescales of these techniques. Furthermore, the excess free volumes calculated from each of these measurements were in excellent agreement with the excess volumes of mixing measured for the IL mixtures investigated. The correspondence of these techniques indicates that the static and dynamic free volume of these liquid mixtures are strongly linked. Consequently, fluxional processes such as hydrogen bonding do not significantly contribute to the free volumes of these liquids compared to the spatial arrangement of ions arising from their size, shape and coulombic attraction. Given the relationship between free volume and transport properties such as viscosity and conductivity, these results provide a link between the structures of IL mixtures, the thermodynamics of mixing and their physicochemical properties.

We observe anharmonic decay of the photoexcited coherent A1g phonon in bismuth to points in the Brillouin zone where conservation of momentum and energy are satisfied for three-phonon scattering. The decay of a coherent phonon can be understood as a parametric resonance process whereby the atomic displacement periodically modulates the frequency of a broad continuum of modes. This results in energy transfer through resonant squeezing of the target modes. Using ultrafast diffuse x-ray scattering, we observe build up of coherent oscillations in the target modes driven by this parametric resonance over a wide range of the Brillouin zone. We compare the extracted anharmonic coupling constant to first principles calculations for a representative decay channel., Comment: 5 pages, 6 figures

International audience; In this "cookbook", we present some recipes of pertinent Resonant Inelastic X-ray Scattering (RIXS) experiments with a focus on hard X-ray range. As a starter, we discuss the new possibilities of investigation of materials introduced by this method. Our 5 recipes focus on spectroscopic innovations or new physical insights, and the dessert looks very briefly at perspectives for the years to come. (C) 2013 Published by Elsevier B.V.

From an engineering perspective, skeletal tissues are remarkable structures because they are lightweight, stiff and tough, yet produced at ambient conditions. The biomechanical success of skeletal tissues is largely attributable to the process of biomineralization — a tightly regulated, cell-driven formation of billions of inorganic nanocrystals formed from ions found abundantly in body fluids. In this Review, we discuss nature's strategies to produce and sustain appropriate biomechanical properties in mineralizing (by the promotion of mineralization) and non-mineralizing (by the inhibition of mineralization) tissues. We review how perturbations of biomineralization are controlled over a continuum that spans from the desirable (or defective in disease) mineralization of the skeleton to pathological cardiovascular mineralization, and to mineralization of bioengineered constructs. A materials science vision of mineralization is presented with an emphasis on the micro- and nanostructure of mineralized tissues recently revealed by state-of-the-art analytical methods, and on how biomineralization-inspired designs are influencing the field of synthetic materials.

Polyethylene glycol (PEG) is an established grafting agent for engineered materials deployed in aqueous environments including biological systems. Phosphorylcholine (PC) has shown promise as a viable strategy for enhancing the biofunctionality of surfaces and structures. Here we developed a new and facile strategy for grafting superparamagnetic iron oxide nanoparticles (IONPs) by phosphonic acid terminated poly(2-(methacryloyloxy)ethyl phosphorylcholine) brushes, synthetized by reversible addition-fragmentation chain transfer (RAFT) polymerization. Properties of covalently bound IONPs with PC, PEG or PEG:PC brush-like structures via a "grafting onto" approach through robust bidentate Fe-O-P bonds were compared. The presence of modified polymers on the functionalized IONP surfaces was proved using both ATR-FTIR and TGA. The resultant synthesized IONPs were characterized for their physicochemical and biological aspects. Interestingly, compared with PEG combs, specifically, PC brushes rendered comparable or enhanced suspendability, stability, biocompatibility and cellular distribution. We attribute these characteristics to the biomimetic nature and larger polarity of PC in contrast to the synthetic and hydrophilic PEG. These synthesis strategies and characterizations may prove beneficial to the design and applications of IONPs in nanobiotechnology and nanomedicine. Refereed/Peer-reviewed

When viewed as an elementary particle, the electron has spin and charge. When binding to the atomic nucleus, it also acquires an angular momentum quantum number corresponding to the quantized atomic orbital it occupies. Even if electrons in solids form bands and delocalize from the nuclei, in Mott insulators they retain their three fundamental quantum numbers spin, charge and orbital. The hallmark of one dimensional physics is a breaking up of the elementary electron into its separate degrees of freedom. The separation of the electron into independent quasiparticles that carry either spin spinons or charge holons was first observed fifteen years ago. Here we report observation of the separation of the orbital degree of freedom orbiton using resonant inelastic X ray scattering on the one dimensional Mott insulator Sr2CuO3. We resolve an orbiton separating itself from spinons and propagating through the lattice as a distinct quasiparticle with a substantial dispersion in energy over momentum, of about 0.2 electronvolts, over nearly one Brillouin zone

Measuring how the magnetic correlations throughout the Brillouin zone evolve in a Mott insulator as charges are introduced dramatically improved our understanding of the pseudogap, non-Fermi liquids and high $T_C$ superconductivity. Recently, photoexcitation has been used to induce similarly exotic states transiently. However, understanding how these states emerge has been limited because of a lack of available probes of magnetic correlations in the time domain, which hinders further investigation of how light can be used to control the properties of solids. Here we implement magnetic resonant inelastic X-ray scattering at a free electron laser, and directly determine the magnetization dynamics after photo-doping the Mott insulator Sr$_2$IrO$_4$. We find that the non-equilibrium state 2~ps after the excitation has strongly suppressed long-range magnetic order, but hosts photo-carriers that induce strong, non-thermal magnetic correlations. The magnetism recovers its two-dimensional (2D) in-plane N\'eel correlations on a timescale of a few ps, while the three-dimensional (3D) long-range magnetic order restores over a far longer, fluence-dependent timescale of a few hundred ps. The dramatic difference in these two timescales, implies that characterizing the dimensionality of magnetic correlations will be vital in our efforts to understand ultrafast magnetic dynamics., Comment: 7 page, 4 figures; to appear in Nature Materials

International audience; The self-assembly kinetics for a norovirus capsid protein were probed by time-resolved small-angle X-ray scattering and then analyzed by singular value decomposition and global fitting. Only three species contribute to the total scattering intensities: dimers, intermediates comprising some 11 dimers, and icosahedral T = 3 capsids made up of 90 dimers. Three-dimensional reconstructions of the intermediate robustly show a stave-like shape consistent with an arrangement of two pentameric units connected by an interstitial dimer. Upon triggering of self-assembly, the biphasic kinetics consist of a fast step in which dimers are assembled into intermediates, followed by a slow step in which intermediates interlock into capsids. This simple kinetic model reproduces experimental data with an excellent agreement over 6 decades in time and with nanometer resolution. The extracted form factors are robust against changes in experimental conditions. These findings challenge and complement currently accepted models for the assembly of norovirus capsids.

International audience; Hybrid polyion complex (HPIC) micelles are nanoaggregates obtained by complexation of multivalent metal ions by double hydrophilic block copolymers (DHBC). Solutions of DHBC such as the poly(acrylic acid)-block-poly(acrylamide) (PAA-b-PAM) or poly(acrylic acid)-block-poly(2-hydroxyethylacrylate) (PAA-b-PHEA), constituted of an ionizable complexing block and a neutral stabilizing block, were mixed with solutions of metal ions, which are either monoatomic ions or metal polycations, such as Al3+, La3+, or Al-13(7+). The physicochemical properties of the HPIC micelles were investigated by small angle neutron scattering (SANS) and dynamic light scattering (DLS) as a function of the polymer block lengths and the nature of the cation. Mixtures of metal cations and asymmetric block copolymers with a complexing block smaller than the stabilizing block lead to the formation of stable colloidal HPIC micelles. The hydrodynamic radius of the HPIC micelles varies with the polymer molecular weight as M-0.6. In addition, the variation of R-h of the HPIC micelle is stronger when the complexing block length is increased than when the neutral block length is increased. R-h is highly sensitive to the polymer asymmetry degree (block weight ratio), and this is even more true when the polymer asymmetry degree goes down to values close to 3. SANS experiments reveal that HPIC micelles exhibit a well-defined core-corona nanostructure; the core is formed by the insoluble dense poly(acrylate)/metal cation complex, and the diffuse corona is constituted of swollen neutral polymer chains. The scattering curves were modeled by an analytical function of the form factor; the fitting parameters of the Pedersen's model provide information on the core size, the corona thickness, and the aggregation number of the micelles. For a given metal ion, the micelle core radius increases as the PAA block length. The radius of gyration of the micelle is very close to the value of the core radius, while it varies very weakly with the neutral block length. Nevertheless, the radius of gyration of the micelle is highly dependent on the asymmetry degree of the polymer: if the neutral block length increases in a large extent, the micelle radius of gyration decreases due to a decrease of the micelle aggregation number. The variation of the R-g/R-h ratio as a function of the polymer block lengths confirms the nanostructure associating a dense spherical core and a diffuse corona. Finally, the high stability of HPIC micelles with increasing concentration is the result of the nature of the coordination complex bonds in the micelle core.

International audience; Rheological and optical microscopy experiments were conducted to monitor the sol-gel transition during gelatinization process of starch granules During the gelatinization phenomenon the grains grow and dissolve into the plasticizer leading to a drastic increase of the elastic modulus (G) and the loss modulus (G") and to their crossover as a consequence of the formation of a physical gel The kinetics of gelation were studied by oscillatory shear experiments and the influence of parameters such as temperature or volume fraction on the gelation process was investigated The variation of the gel time with temperature for any composition of glycerol/starch suspension was predicted from the Dickinson model The relaxation exponent (n = 0 73) was calculated by varying the frequency at constant volume fraction and temperature The deduced value indicates that the gelation process is described by percolation theory Apparent activation energies were estimated from the rheological data as well as from the optical microscopy data and were found to be nearly the same At last the ability of two polyols to act as plasticizer was assessed and compared to that of glycerol (C) 2010 Elsevier Ltd All rights reserved

International audience; This paper presents a study of the strain hardening of a 7000 series aluminium alloy. A wide variety of microstructural states are tested both in uniaxial tension and by performing Bauschinger tests. Their microstructural features are evaluated quantitatively in terms of precipitate size and volume fraction using small-angle X-ray scattering. A physically-based model for strain hardening, using a modified version of the Kocks-Mecking-Estrin formalism, is presented for the precipitation states that exhibit precipitate bypassing. The model takes explicitly into account the microstructural information and describes in detail the mechanisms governing the storage, stability and annihilation of Orowan loops around the precipitates. It describes both the uniaxial and the strain-reversal tests, by evaluating separately the kinematic and isotropic contributions to strain hardening and using an appropriate mixing law. In addition, the transient of strain-reversal Bauschinger tests is discussed with respect to the effect of precipitates on strain reversibility. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

International audience; Using a combination of experimental techniques, including anomalous small-angle scattering and atom-probe tomography, the evolution of precipitate microstructures during the different steps of retrogression and re-ageing (RRA) heat treatments of an Al-Zn-Mg-Cu alloy has been systematically evaluated. Quantitative information on the morphology, scale and chemistry of the precipitates provide new insight into the mechanisms at work during this process. It is shown that both the final chemistry and precipitate size distribution are different in the final RRA temper compared to classical heat treatments, with the presence of small clusters nucleated during the re-ageing step, and an average precipitate composition richer in Cu, together with a matrix enrichment in Zn, related to the difference in diffusivity between the two solute atoms. The mechanisms of precipitate evolution during the reversion and re-ageing steps are discussed in light of the influence of the process parameters.

International audience; The composition of precipitates in three alloys of the Al-Zn-Mg-Cu system has been investigated for different heat treatments, including peak-aged and over-aged states as well as near-equilibrium conditions, by combining atom probe tomography and systematic anomalous small-angle X-ray scattering experiments. We show that the concentration of Cu in the precipitates changes during heat treatments and is alloy dependent. At low ageing temperature (120 degrees C) the Cu content in the precipitates is close to the alloy content. The precipitate Cu content is shown to increase with increasing temperature and Cu alloy content. We show that in near-equilibrium conditions the precipitate compositions are 33 at.% in Mg, about 15 at.% in Al, about 13 at.% in Cu and balance Zn. Our results strongly suggest that the gradual incorporation of Cu in the precipitates during the heat treatment is essentially related to the slower diffusivity of this element in aluminium.

A method allowing the evaluation of the solvophilic/solvophobic character of polyelectrolytes from their conformation in solution is discussed. Analyzed systems are salt-free aqueous solutions of natural copolysaccharides with controlled chemical structures. Small-angle X-ray scattering diagrams revealed their conformation by the "polyelectrolyte peak". The study of this peak allowed the determination of c(b), the crossover concentration associated with the transition between the two structural organization regimes predicted by the scaling model of hydrophobic polyelectrolytes developed by Dobrynin and Rubinstein.(1) A structural law of behavior as a function of the chain primary structure is built for chitosan, showing an increasing hydrophobic character when the fraction of N-acetyl-D-glucosamine residues (DA) increases. The results concerning this random copolymer are compared with those obtained for hyaluronan. Consistently, in the case of alginates, the relative content of the constitutive units is shown not to influence the polymer hydrophobicity.