HAL Portal ESPCI (Ecole Supérieure de Physique et de Chimie Industrielles)
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Dynamic Heterogeneity of Short Semi-crystalline Polymer Chains during Recrystallization
No full textInternational audienceThe instant crystallization of semi-crystalline polymers have become possible following the recent advances in Fast Scanning Calorimetry (FSC) and enables to make a bridge between the time scale available experimentally with those accessible with computer simulations. Although the FSC observations have provided new information on the crystallization kinetics and evolution of the crystals, the molecular details on the chain exchange events between ordered and disordered domains of crystals have remained elusive. Using molecular dynamics simulations, we examined the detailed chain dynamics and thermodynamics of polyamide 6 (PA6) system under two heating treatments. (i) Quenching PA6 melt deeply below the melting temperature T m and (ii) annealing the resulting quenched system to a temperature close to T m . We categorized the chains into mobile amorphous fraction (MAF) and rigid amorphous fraction (RAF), based on the length of consecutive chain's bond angles in trans state. In the deep quenched system close to the glass transition temperature T g , the mobility of the MAF chains are strongly suppressed and they remain in glassy state. However, upon rising the temperature close to melting temperature, the system undergoes recrystallization leading to coexistence of RAF and supercooled liquid MAF chains. The highly mobile unentangled MAF chains explore the interphase domains, and during the late-stage of crystallization, they are thermally translocated into the lamellae by reducing the fold number of RAF chains. The chain mobility in the annealed system could potentially lead to improved biodegradation in semi-crystalline chains
Electroluminescence and energy transfer mediated by hyperbolic polaritons
No full textData are publicly available on Zenodo at 10.5281/zenodo.10625437https://zenodo.org/records/14382617International audienceUnder high electrical current, some materials can emit electromagnetic radiation beyond incandescence. This phenomenon, referred to as electroluminescence, leads to the efficient emission of visible photons and is the basis of domestic lighting devices (for example, light-emitting diodes)1,2. In principle, electroluminescence can lead to mid-infrared emission of confined light–matter excitations called phonon polaritons3,4, resulting from the coupling of photons with crystal lattice vibrations (optical phonons). In particular, phonon polaritons arising in the van der Waals crystal hexagonal boron nitride (hBN) present hyperbolic dispersion, which enhances light–matter coupling5,6. For this reason, electroluminescence of hyperbolic phonon polaritons (HPhPs) has been proposed as an explanation for the peculiar radiative energy transfer within hBN-encapsulated graphene transistors7,8. However, as HPhPs are locally confined, they are inaccessible in the far field, and as such, any hint of electroluminescence has been based on indirect electronic signatures and has yet to be confirmed by direct observation. Here we demonstrate far-field mid-infrared (wavelength approximately 6.5 μm) electroluminescence of HPhPs excited by strongly biased high-mobility graphene within a van der Waals heterostructure, and we quantify the associated radiative energy transfer through the material. The presence of HPhPs is revealed by far-field mid-infrared spectroscopy owing to their elastic scattering at discontinuities in the heterostructure. The resulting radiative flux is quantified by mid-infrared pyrometry of the substrate receiving the energy. This radiative energy transfer is also shown to be reduced in hBN with nanoscale inhomogeneities, demonstrating the central role of the electromagnetic environment in this process
Using lateral dispersion to optimise microfluidic trap array efficiency
No full textInternational audienceMicrofluidic trapping arrays have proven to be efficient tools for various applications that require working at the single-cell level, such as cell-cell communication or fusion. Although several hydrodynamic trapping devices have already been optimised, two-dimensional (2D) single-layer trapping arrays with high trap densities remain partially inefficient. Specifically, many traps remain empty, even after prolonged injection, which drastically reduces the number of samples available for post-treatment. These unfilled traps result from the symmetrical nature of the flow around the traps, and breaking this symmetry enhances capture efficiency. In this study, we use a numerical approach to show that optimal geometries can significantly increase filling efficiency and a preliminary experimental test confirming our approach is provided. We show that these improvements are achieved by promoting lateral dispersion of particles, facilitated either through an optimised oblique flow or by introducing disorder into the spatial arrangement of traps without specific inlet/outlet adjustment
Programmable metasurfaces for future photonic artificial intelligence
No full textInternational audiencePhotonic neural networks (PNNs), which share the inherent benefits of photonic systems, such as high parallelism and low power consumption, could challenge traditional digital neural networks in terms of energy efficiency, latency and throughput. However, producing scalable photonic artificial intelligence (AI) solutions remains challenging. To make photonic AI models viable, the scalability problem needs to be solved. Large optical AI models implemented on PNNs are only commercially feasible if the advantages of optical computation outweigh the cost of their input-output overhead. In this Perspective, we discuss how field-programmable metasurface technology may become a key hardware ingredient in achieving scalable photonic AI accelerators and how it can compete with current digital electronic technologies. Programmability or reconfigurability is a pivotal component for PNN hardware, enabling in situ training and accommodating non-stationary use cases that require fine-tuning or transfer learning. Co-integration with electronics, 3D stacking and large-scale manufacturing of metasurfaces would significantly improve PNN scalability and functionalities. Programmable metasurfaces could address some of the current challenges that PNNs face and enable next-generation photonic AI technology
Numerical Validation of a Model of Antenna-Related Losses Within Reverberation Chambers
No full textInternational audienceReverberation Chambers (RCs) are widely used to perform electromagnetic testings. The contribution of antennas to the overall RC quality factor is of particular interest both to predict the amount of losses brought by antennas during measurements, as well as to perform noninvasive antenna characterisation. In this communication, we present a recently-proposed model, based on antenna scattering-matrix theory, which take into account both the structural and the antenna modes as well as the complex interactions between the two. In particular, we show, numerically, that it is possible to retrieve both the radiation efficiency and the input impedance, from the evaluation of the antenna contribution to the RC quality factor for a set of different loads
Physio-fUS: a tissue-motion based method for heart and breathing rate assessment in neurofunctional ultrasound imaging
No full textInternational audienceBackground Recent studies have shown growing evidence that brain function is closely synchronised with global physiological parameters. Heart rate is linked to various cognitive processes and a strong correlation between neuronal activity and breathing has been demonstrated. These findings highlight the significance of monitoring these key physiological parameters during neuroimaging as they provide valuable insights into the overall brain function. Today, in neuroimaging, assessing these parameters requires additional cumbersome devices or implanted electrodes. Here we demonstrate that ultrasonic neurofunctional imaging data alone is sufficient to extract these parameters.Methods In this work, we performed ultrafast ultrasound imaging in male rodents and human neonates, and we extracted heart and breathing rates from local tissue motion assessed by raw ultrasound data processing. Such "Physio-fUS" automatically selects two specific and optimal brain regions with pulsatile tissue signals to monitor such parameters.Findings We validated the correspondence of these periodic signals with heart and breathing rates assessed using gold-standard electrodes in anaesthetised rodents. We extracted heart and breathing rates in sleeping rats and heart rate in rats moving freely in an arena. We also validated Physio-fUS imaging in sleeping human newborns using conventional ECG.Interpretation We show the potential of fUS imaging as an integrative tool for simultaneously monitoring physiological parameters during neurofunctional imaging. Beyond the technological improvement, it could enhance our understanding of the link between breathing, heart rate and neurovascular activity in preclinical research and clinical functional ultrasound imaging.</div
Mechanosynthesis and Polymerization of Styrene Derivatives Based on Building Blocks of Lignin
No full textInternational audienceGiven the constraints dictated by the environment and the current policies, it is urgent to conceive and developnovel molecular building blocks and materials from bio-sourced platforms in order to compete and replace thoseobtained from petroleum sources (styrene, bisphenol A, etc.). Bio-sourced monomers can be obtained from thetransformation of molecules extracted from five main sources, namely terpenes, carbohydrates, lignin, proteins andlipids from animal, plant, or sea origin. Thanks to the presence of alcohol, acid or amine functional groups, thesebio-sourced molecules can often be polymerized by condensation reaction and yield bio-based polyesters orpolyamides with mechanical properties that can compete with their petroleum-based counterparts.Step-growth polymerization remains therefore the most explored pathway to produce bioplastics nowadays.Recently, the number of publications reporting free-radical chain-reaction polymerization (FRP) of bio-monomershas strongly increased. However, it remains still limited, probably due to the little number of readily availableradically polymerizable bio-sourced structures. In this context, lignin, the second most abundant natural polymericconstituent of wood, accounting for around 20% of the lignocellulosic biomass11 and currently discarded as wasteby the paper industry, appears to be a suitable candidate. Indeed, the controlled degradation of lignin allows toproduce biofuels, precursors for organic synthesis or oligomers that can be applied to prepare functional materials.Among those examples, the compounds obtained from lignin degradation represent a promising alternative todesign bio-sourced polymers displaying interesting thermo-mechanical properties thanks to the presence ofaromatic cycles.In this communication, we report the synthesis of polystyrenes prepared in three steps from vanillin, 4-hydrobenzaldehyde, and syringaldehyde, compounds that can be obtained through lignin depolymerization underoxidative conditions. The synthesis involves the conversion of these biosourced platforms into polymerizablestyrene derivatives through a methylation of the hydroxyl group followed by an olefination of the aldehyde function.The monomers were first synthesized under conventional conditions using solvents. Then, the synthesis wasimproved from the sustainability point of view by using a ball mill under solventless conditions, generating muchless waste in the process. Mechanochemistry has successfully been transposed from material sciences to organicchemistry in the past decades. Compared to conventional procedures and solvent-based reactions, it usesmechanical energy to induce a chemical reaction in solvent-free conditions and can afford shorter reaction times,higher yields and more sustainable process.The three monomers were then converted into biosourced homopolymers through free radical polymerization inbulk, providing functional polystyrene derivatives with thermal properties comparable to those of common petrosourced polystyrene
Experiments on water-wave interactions with a horizontal submerged elastic plate
No full textInternational audienceThis article explores how a submerged elastic plate, clamped at one edge, interacts with water waves. Submerged elastic plates have been considered as potentially effective design elements in the development of wave energy harvesters but their behaviour in a wave field remains largely unexplored, especially experimentally. Positioned at a fixed depth in a wave tank, the flexible plate demonstrates significant wave reflection capabilities, a characteristic absent in rigid plates of identical dimensions. The experiments thus reveal that plate motion is crucial for wave reflection. Sufficiently steep waves are shown to induce a change in the mean position of the plate, with the trailing edge reaching the free surface in some cases. This configuration change is found to be particularly efficient to break water waves. These findings contribute to understanding the potential of elastic plates for wave energy harvesting and wave attenuation scenarios
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
Modeling the dynamics of aeolian meter-scale bedforms induced by bed heterogeneities
No full textInternational audienceDesert surfaces are typically non uniform, with individual sand dunes generally surrounded by gravel or non-erodible beds. Similarly, beaches vary in composition and moisture that enhances cohesion between the grains. These bed heterogeneities affect the aeolian transport properties greatly, and can then influence the emergence and dynamics of bedforms. Here, we propose a model that describes how, due to transport capacity being greater on consolidated than erodible beds, patches of sand can grow, migrate and spread to form bedforms with meter-scale length. Our approach has a quantitative agreement with high-resolution spatio-temporal observations, where conventional theory would predict the disappearance of these small bedforms. A crucial component of the model is that the transport capacity does not instantly change from one bed configuration to another. Instead, transport capacity develops over a certain distance, which thereby determines the short-term evolution of the bedform. The model predicts various stages in the development of these meter-scale bedforms, and explains how the evolution of bed elevation profiles observed in the field depends on the duration of the wind event and the intensity of the incoming sand flux. Our study thus sheds light on the initiation and dynamics of early-stage bedforms by establishing links between surface properties, emerging sand patterns and protodunes, commonly observed in coastal and desert landscapes