Ref HAL: hal-05349562_v1
DOI: 10.1180/clm.2025.10012
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This study investigates the influence of interlayer cations on the thermodynamics and sorption mechanisms of water in a reference Wyoming montmorillonite. The behaviour of the montmorillonite exchanged with monovalent cations (Li + , Na + , K + , Rb + , Cs + ) or divalent cations (Mg 2+ , Ca 2+ , Ba 2+ ) is compared. The analysis combines X-ray diffraction (XRD), water sorption isotherms at various temperatures and mid-infrared spectroscopy. Li + , Mg 2+ and Ca 2+ promote greater water uptake and swelling, whereas K + , Rb + and Cs + significantly limit these processes. The behaviour of Na + and Ba 2+ stands out, demonstrating intermediate water uptake and high swelling. Mid-infrared spectral analysis supports these observations. It is shown that a cation’s effect on water uptake and swelling correlates best with the product of its elementary charge and ionic radius rather than with other properties such as the electrostatic potential, solvation enthalpy or chemical hardness. However, differences in isotherm shapes, hysteresis between adsorption and desorption and the variation of isosteric heat with water content suggest the presence of two distinct sorption mechanisms: one involving Li + , Cs + , Mg 2+ , Ca 2+ and Ba 2+ , and another involving Na + , K + and Rb + . These findings indicate that isotherm shape and swelling alone do not directly reflect water uptake capacity. These findings thus outline that the chaotropic (structure-breaking) or kosmotropic (structure-making) nature of the cations, along with the complex interplay between cation hydration and TOT layer attraction, may explain the complex observed differences.

Ref HAL: hal-05347389_v1
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Gravity affects the flow and the behavior at rest of complex fluids and flows by inducing sedimentation, drainage, and interfacial deformation, which can mask more fundamental physical processes. On Earth, standard countermeasures against gravity come with limitations in terms of possible formulations or the quality and homogeneity of the applied strain. Alternatively, one can run these experiments in free-fall or in orbit where the effects of gravity are canceled i.e., under microgravity conditions. In this short review, we present several European Space Agency-led projects of interest to rheologists that leverage microgravity environments: FAST/FASTER , which studies interfacial rheology using Capillary Pressure Tensiometers; SMD-FOAM, fundamental experiments on foam coarsening ; SMD-PASTA and SEEDS, aimed at understanding the dynamics of emulsion droplets, its evolution and microrheology using Diffusing Wave Spectroscopy; results associated with studies on granular materials in microgravity, including AstEx and CompGran; COLIS, which examines the thermally driven perturbation of soft colloidal glasses monitored by Dynamic Light Scattering; BIOMICS/KRABS, investigating the aggregation and migration of soft particles and red blood cells under flow. Microgravity experiments allowed for high-precision measurements of interfacial viscoelasticity, detailed studies of emulsion aging and drop coalescence, observed plastic rearrangements in colloidal glasses, characterized the dynamics under flow of red blood cell analogues, and rationalized the impact of gravity on convection and fluidization in agitated granular matter. Collectively, these experiments demonstrate the complementarity and the relevance of ESA's microgravity platforms in expanding the frontiers of soft matter rheology.

Commentaires: Submitted to Journal of Rheology (revised version)

Ref HAL: hal-05342528_v1
Ref Arxiv: 2501.16736
DOI: 10.1103/PhysRevMaterials.9.024001
Ref. & Cit.: NASA ADS
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Ref HAL: hal-05347307_v1
DOI: 10.1371/journal.pone.0333021
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Plastic pollution is a major and global threat to ecosystems and human health, resulting from the spreading and breakdown of plastic litter in the environment. In an aquatic environment, the first causes of this degradation are exposure to natural ultraviolet light and abrasion or collisions in the water. The extent of such degradation on a plastic object after a given time remains very difficult to quantify, especially regarding the relative production of microplastics, nanoplastics and soluble species along with volatile compounds. All of these degradation products may contribute differently to environmental pollution. Therefore, when evaluating the pollution caused by plastic objects, we should consider how much of each byproduct is generated. We propose a novel method based on conservation of the carbon mass during the degradation process. This approach is the first to enable quantification of carbon retrieved in each type of degradation product (Microplastics, Nanoplastics, Solubles, Volatile Compounds), as well as its evolution with exposure time. By applying this method to polypropylene granules, we demonstrate its effectiveness in tracking carbon footprint throughout the aging process. One of the unexpected results of this study is to show that the amount of carbon released in volatile form is far from negligible (17%) compared to MP (55%). The procedure we present is general enough to be applied to any type of polymer, and can be a valuable tool for assessing the amount of by-products of a given size released into the environment.

Ref HAL: hal-05344568_v1
Ref Arxiv: 2502.03166
DOI: 10.1103/dvbq-9z5f
Ref. & Cit.: NASA ADS
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Interfacial Dzyaloshinkii-Moriya interaction (DMI) is a key ingredient in the stabilization of chiral magnetic states in thin films. Its sign and strength often determine crucial properties of magnetic objects, like their topology or how they can be manipulated with currents. A few experimental techniques are currently available to measure DMI quantitatively, based on the study of domain walls, spin waves, or spin-orbit torques. In this work, we propose a qualitative variant of spin wave methods. We rely on magnetic noise from confined thermal spin waves in domain walls and skyrmions in perpendicularly magnetized thin films, which we probe with scanning NV center relaxometry. We show both numerically and experimentally that the sign of the DMI can be inferred from the amplitude of the detected noise, which is affected by the non-reciprocity in the spin wave dispersion. Furthermore, we also demonstrate that the noise distribution around the contour of magnetic skyrmions reveals their Néel/Bloch nature, giving therefore also insight into the strength of DMI involved in their stabilization.

Ref HAL: hal-05344552_v1
DOI: 10.1016/j.polymer.2024.127927
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A combined SAXS-shear analysis of polymer nanocomposites for the first time between parallel plates is presented. This set-up allows investigating microstructural changes accompanying macroscopic rheological phenomena, such as the Payne effect. The latter is known to induce filler network destruction and subsequent flocculation when the shear strain amplitude is increased or decreased, respectively. First, a detailed SAXS analysis of the microstructure of carbon black in styrene-butadiene nanocomposites is applied to a series of increasing filler loading. The average size and mass of primary particles and small aggregates are estimated using a model of inter-aggregate polydisperse hardsphere interactions. In a second time, the impact of a new geometry of the shear experiments with a horizontal X-ray beam passing through a disc-shaped nanocomposite on the SAXS pattern is analyzed in terms of sample heterogeneity (different positions), anisotropy (orientations), and sample thickness (transmission and heterogeneity). Application of our quantitative analysis shows that hot molding induces a slight anisotropy of the aggregate shapes into prolate ellipsoids oriented parallel to the rubber sheet. The Payne effect is then followed by scattering, surprisingly showing no modification of the intensity under oscillatory shear. Thus, the aggregate structure observed on the scale of standard SAXS is not broken up during Payne experiments, hinting at either an averaging effect over oscillation periods, or to the reorganization of large-scale agglomerate or network structures.

Ref HAL: hal-05344531_v1
DOI: 10.1021/acsami.5c11985
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Mesoporous systems are ubiquitous in membrane science and applications due to their high internal surface area and tunable pore size. A new synthesis pathway of hydrolytic ionosilica films with mesopores formed by ionic liquid (IL) templating is proposed and compared to the traditional nonhydrolytic strategy. For both pathways, the multi-scale formation of pores has been studied as a function of IL content, combining results of thermogravimetric analysis (TGA), nitrogen sorption, and small-angle X-ray scattering (SAXS). The combination of TGA and nitrogen sorption provides access to ionosilica and pore volume fractions, with contributions of meso-and macropores. We then elaborate an original and quantitative geometrical model to analyze the SAXS data based on small spheres (Rs = 1 -2 nm) and cylinders (Lcyl = 10 -20 nm) with radial polydispersity provided by the nitrogen sorption isotherms. As a main result, we found that for a given incorporation of templating IL, both synthesis pathways produce very similar pore geometries, but the better incorporation efficacy of the new hydrolytic films provides a higher mesoporosity. Our combined study provides a coherent view of mesopore geometry, and thereby an optimization pathway of porous ionic membranes in terms of accessible mesoporosity contributing to the specific surface. Possible applications include electrolyte membranes of improved ionic properties, e.g., in fuel cells and batteries, as well as molecular storage.