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Droplet-on-demand using a positive pressure pulse
No full textInternational audienceDroplet generation under steady conditions is a common microfluidic method for producing biphasic systems. However, this process works only over a limited range of imposed pressure: beyond a critical value, a stable liquid jet can instead form. Furthermore, for a given geometry the pressure conditions set both the generation rate of droplets and their volume. Here, we report on-demand droplet production using a positive pressure pulse to the dispersed-phase inlet of a flow-focusing geometry. This strategy enables confined droplet generation within and beyond the pressure range observed under steady conditions, and decouples volume and production rate. In particular, elongated plugs not possible under steady conditions may be formed when the maximal pressure during the pulse reaches the jet regime. The measured volume of droplets-on-demand, as well as the onset of droplet generation are both captured with a simple model that considers hydraulic resistances. This work provides a strategy and design rules for processes that require individual droplets or elongated plugs in a simple microfluidic chip design
Relaxation of the Adsorbed Material and Shadowing Effects on the Shape and Size of Electrodeposited Dendrites
No full textInternational audienceMaterials with dendritic morphologies exhibit large surface areas that improve the catalytic, optical, and wetting properties but have ambiguous effects in batteries, so modeling their growth may help find the best operation conditions in each case. Kinetic Monte Carlo simulations are used here to study a metal electrodeposition model that represents the interplay between diffusive cation flux in the electrolyte and surface diffusion of adsorbed atoms (adatoms) with electrodes perpendicular to the gradient of the electrolyte concentration and different crystallographic orientations. In FCC lattices, dendrites with a pine tree shape are formed for all orientations, with dominant (111) surfaces and with trunks propagating in [001] and equivalent directions. However, with ( 110) and ( 111) substrates, secondary branches do not grow because the inclined primary branches block the cation flux (shadowing effect), so the dendrites may have a leaf-like shape. Some morphologies obtained here resemble those of the silver and gold electrodeposits. The extension to electrodeposition of HCP crystals with (0001) substrates shows the formation of leaf-like dendrites with a hexagonal symmetry. In both lattices, hierarchically organized structures appear for model parameters that warrant large diffusion lengths of adsorbed atoms on flat planes (typically coordination numbers n ≤ 4) and their stability at low-energy configurations (n ≥ 7). Average dendrite widths scale approximately with the diffusion length from adsorption to permanent incorporation to the crystal. These results show that dendrite widths are directly related to the relaxation of the electrodeposited material, and their crystallography is controlled by the energetics of the relaxation, but their visual appearance may depend on their angles with the electrode. In the range of model parameters where the coordination number weakly affects the diffusion of adsorbed atoms, the dendrites become rounded and have flower-like shapes. Possible effects of the orientation on the physicochemical properties of thin dendritic films are discussed
Fabrication of COC micromodels with wettability heterogeneities: method and influence on fluid transport
No full textInternational audienceWettability plays a key role in multiphase fluid flow through porous media, significantly influencing geological processes such as CO2 sequestration, groundwater remediation, or oil recovery. Micromodels, i.e. microfluidic porous media, have advanced the study of fluid flows in porous media by enabling direct visualisation of these processes. However, the influence of wettability heterogeneities on fluid flows in porous media remains underexplored in the literature, with studies focusing primarily on homogeneous wettabilities. In this study, we propose a complete method to manufacture micromodels with controllable, heterogeneous wettabilities. This work is at the crossroads of three different fields: microfabrication, surface treatment and fluid transport in porous media. The micromodels are made from a transparent polymer, cyclic olefin copolymer (COC), using hot-embossing. A plasma enhanced chemical vapor deposition (PECVD) process with a tetraethyl orthosilicate (TEOS) precursor is then used locally to reduce the COC's wettability. The durability, degree, and localisation of the deposition are quantitatively assessed with scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDS), IR spectroscopy, and contact angle measurements. Our fabrication method successfully produced mixed-wet micromodels with easily controllable wettability patterns. Additionally, our study also presents a qualitative analysis of the impact of wettability heterogeneities on multiphase flows for oil, water, and water-in-oil emulsion injections. The location of the treated surface areas is shown to strongly impact emulsion stability and transport
Nearfield control over magnetic light-matter interactions
No full textInternational audienceLight-matter interactions are frequently perceived as predominantly influenced by the electric field, with the magnetic component of light often overlooked. Nonetheless, the magnetic field plays a pivotal role in various optical processes, including chiral light-matter interactions, photon-avalanching, and forbidden photochemistry, underscoring the significance of manipulating magnetic processes in optical phenomena. Here, we explore the ability to control the magnetic light and matter interactions at the nanoscale. In particular, we demonstrate experimentally, using a plasmonic nanostructure, the transfer of energy from the magnetic nearfield to a nanoparticle, thanks to the subwavelength magnetic confinement allowed by our nano-antenna. This control is made possible by the particular design of our plasmonic nanostructure, which has been optimized to spatially decouple the electric and magnetic components of localized plasmonic fields. Furthermore, by studying the spontaneous emission from the Lanthanide-ions doped nanoparticle, we observe that the measured field distributions are not spatially correlated with the experimentally estimated electric and magnetic local densities of states of this antenna, in contradiction with what would be expected from reciprocity. We demonstrate that this counter-intuitive observation is, in fact, the result of the different optical paths followed by the excitation and emission of the ions, which forbids a direct application of the reciprocity theorem
Advances in dynamic and batch processing of PIXE spectra
No full textInternational audienceWe present here the advances on two custom-built software programs for PIXE spectra processing, both of them based on the GUPIX package. The first one, named LivePIXE, is a standalone executable that has been implemented in the New AGLAE data acquisition system to process dynamically PIXE spectra during recording, almost in real-time. It allows to verify if the selected area of the object is relevant for the analysis and it provides a first interpretation of the PIXE results in order to orientate further analysis. The second program presented here is an updated version of the TrauPIXE software, which we had previously developed to process series of recorded PIXE spectra. As different X-ray absorbers can be installed in front of the detectors, each element of interest in the sample can be measured with different detection limits and uncertainties. This updated version selects the most precise element concentrations from all the PIXE results. It can also take into account the elemental concentrations obtained simultaneously by PIGE or/and RBS and incorporate them during the PIXE processing and into the final compositional table
Ultralow-Temperature Thermodynamics and Optical Coherence of Narrow Linewidth Optical Emitters
No full textThe coherence properties of optical emitters in crystals are critical for quantum technologies and optical frequency metrology. Cooling to sub-kelvin temperatures can significantly enhance their coherence, making it essential to identify the key parameters governing emitter and host crystal behavior in this ultra cold regime. We investigate a Czochralski-grown europium doped yttrium orthosilicate crystal, and we report measurements of the heat capacity, a parameter fundamental to evaluating thermal noise limits in metrology schemes based on spectral hole stabilization in such samples. In parallel, we characterize optical coherence via photon echo measurements as a function of temperature. Below 1 K, where phonon contributions diminish, two-level systems (TLS) associated with crystal imperfections may emerge as a limiting factor. A linear-in-temperature term in the heat capacity serves as a signature of TLS, and from our data, we establish an upper bound on this contribution. This, combined with the optical homogeneous linewidth from photon-echo measurements being constant in the interval from 300 mK to 2 K demonstrates a minimal TLSrelated effects in our sample. These findings highlight the promise of ultralow-temperature operation for enhancing the performance of optical quantum devices based on doped crystals
Transfer learning assessment of small datasets relating manufacturing parameters with electrochemical energy cell component properties
No full textInternational audienceThe performance of electrochemical cells for energy storage and conversion can be improved by optimizing their manufacturing processes. This can be time-consuming and costly with the traditional trial-and-error approaches. Machine Learning (ML) models can help to overcome these obstacles. In academic research laboratories, manufacturing dataset sizes can be small, while ML models typically require large amounts of data. In this work, we propose a simple but still novel application of a Transfer Learning (TL) approach to address these manufacturing problems with a small amount of data. We have tested this approach with pre-existing experimental and stochastically generated datasets. These datasets consisted of component properties (e.g., electrode density) related to different manufacturing parameters (e.g., solid content, comma gap, coating speed). We have demonstrated the robustness of our TL approach for manufacturing problems by achieving excellent prediction performance for electrodes in lithium-ion batteries and gas diffusion layers in fuel cells
Crystalline vs. amorphous Li4PS4I: Impact of structure on ionic transport and performances in solid-state battery
No full textInternational audienceAll-solid-state batteries (ASSBs) are emerging as next-generation energy storage solutions due to their potential advantages, including enhanced safety, higher energy density, and broader operational temperature ranges. Among various solid electrolytes, amorphous and crystalline Li4PS4I, have attracted interest due to their predicted high conductivity, and high moisture-tolerance. However, experimental studies have reported a wide variation in conductivity values for Li4PS4I, ranging from 0.03 to 3.5 mS.cm−1 at 298 K which are significantly lower than theoretical predictions. Herein, by employing a combination of X-ray diffraction (XRD), 31P magic-angle spinning nuclear magnetic resonance (31P MAS NMR), electrical impedance spectroscopy (EIS), we demonstrate that controlling the crystallinity of Li4PS4I plays a crucial role in its electrochemical performance. Pair distribution function (PDF) analysis reveals the differences in local atomic arrangements between amorphous and crystalline Li4PS4I. Additionally, the analysis indicates that mechanical milling alters the local environment of PS4 tetrahedra and iodide anions, which may explain the discrepancy in conductivity. Furthermore, ASSBs incorporating amorphous-ceramic Li4PS4I in the cathode composite exhibit enhanced cycling stability compared to amorphous Li4PS4I. These findings underscore the potential of tuning crystallinity as an effective approach to optimize the ionic transport properties and cycling performance of ASSBs, paving the way for further advancements in solid electrolytes
Lanthanide‐mediated Defluorinative Transformations of Trifluoromethylated Benzofulvenes: Access to Functionalized Difluoroalkenes and Mechanistic Insights
No full textInternational audienceAbstract Accessing difluorinated organic molecules via selective C−F bond activation in CF 3 ‐containing substrates has become a valuable synthetic pathway. The combination of lanthanide metals (lanthanum, dysprosium) with Lewis acids (AlCl 3 , LaI 3 ) allows the efficient regio‐ and stereoselective transformation of CF 3 ‐benzofulvenes into a range of versatile difluoroalkenes proceeding via ϵ,ϵ‐difluoropentadienyl lanthanide or aluminium species. The reaction of these organometallic intermediates towards ketones and nitroalkenes is herein reported and analyzed in relation to previous studies on aldehydes. The influence of steric and electronic factors of the organic substrates but also of the lanthanide metals and Lewis acids on the regio and stereoselective reaction is highlighted and corroborated by in‐depth DFT studies. The resulting difluorinated homoallylic alcohols and nitroalkanes were further functionalized to new benzofulvenes and their reactivity explored
Measurement of Electrolyte Self-Diffusion in Laser Structured Electrodes
No full textInternational audienc