A novel and versatile way to prepare thin, transparent, flexible and homogeneous films of advanced and multi-component materials has been developed by our research group. The so-called liquid/liquid interfacial route (LLIR) is a new pathway to design materials combining synthesis and processing in one single-pot and single-step, allowing the production of multi-components and multi-functional thin films for application in different fields. This talk will demonstrate the huge potentiality of LLIR to prepare novel and exclusive multicomponent films of different mater, highlighting conducting polymers- and 2D-based nanocomposites. Application of the resulting materials in different fields as electrodes in aqueous and transparent Na- or K-ion batteries, transparent electrodes, electrochromic displays, catalysts and sensors will also be shown.

Gaugino condensation on D-branes wrapping internal cycles gives a mechanism to stabilize the associated moduli. According to the effective field theory, this gives rise, when combined with fluxes, to supersymmetric AdS4 solutions. In this paper we provide a ten-dimensional description of these vacua. We first find the supersymmetry equations for type II AdS4 vacua with gaugino condensates on D-branes, in the framework of generalized complex geometry. We then solve them for type IIB compactifications with gaugino condensates on smeared D7-branes. We show that supersymmetry requires a (conformal) Calabi-Yau manifold and imaginary self-dual three-form fluxes with an additional (0,3) component. The latter is proportional to the cosmological constant, whose magnitude is determined by the expectation value of the gaugino condensate and the stabilized volume of the cycle wrapped by the branes. This confirms, qualitatively and quantitatively, the results obtained using effective field theory. We find that exponential separation between the AdS and the KK scales seems possible as long as the three-form fluxes are such that their (0,3) component is exponentially suppressed. As for the localized solution, it requires going beyond SU(3)-structure internal manifolds. Nevertheless, we show that the action can be evaluated on-shell without relying on the details of such complicated configuration. We find that no “perfect square” structure occurs, and the result is divergent. We compute the four-fermion contributions, including a counterterm, needed to cancel these divergences.

Despite its great triumph, nowadays it is well-know that the Standard Model (SM) of particle physics remains an incomplete theory, as a range of unsolved questions persist. In this context, the search for phenomena that lie beyond the SM gains even greater significance. Although originally such searches focused on the evidence of new heavy particles, more recently several experiments have become capable of probing dark sectors with feebly interacting light particles, pushing particle physics to the 'intensity frontier' era. In this talk, I will discuss the theory and phenomenology of different minimal BSM extensions related to the three possible renormalizable interactions (‘portals’) connecting the new dark sector and the SM. In particular, I will focus on models that introduce new light particles such as the dark photon, the dark Higgs, and axion-like-particles.

Nous avons étudié la force de Casimir-Lifshitz (CLF) entre des nanostructures à base de graphène, à l'équilibre et hors équilibre thermique, i.e. entre deux feuilles de graphène posées sur un substrat diélectrique se faisant face dans diverses conditions thermiques. Nous avons également étudié la CLF entre deux réseaux de graphène à l'équilibre thermique. Pour analyser ce problème, nous avons utilisé l'approche de la matrice de diffusion (S-matrix), qui nécessite des méthodes numériques efficaces pour être calculée. Parmi ces méthodes, nous avons adapté la Méthode Modale de Fourier équipée de fonctions de base locales (FMM-LBF : Fourier Modal Method - Local basis Functions) en incidence conique. De plus, nous avons étendu cette méthode pour analyser des structures cylindriques recouvertes de bandes de graphène [1]. En ce qui concerne la CLF entre des réseaux de graphène posés sur des substrats diélectriques, nous avons observé une variation notable de celle-ci en fonction du potentiel chimique. Par la suite, nous avons examiné son comportement non-additif et constaté que, pour de petites séparations (d = 60 nm), la non-additivité est relativement faible. En conséquence, nous pouvons utiliser en toute confiance une méthode additive beaucoup plus directe et rapide pour calculer la force avec une précision de quelques pourcents. Cependant, la situation est tout à fait différente pour de plus grandes séparations (d = 200 nm). À cette distance, il y a un effet non-additif significatif, entraînant des écarts allant jusqu'à 30% par rapport à la prédiction additive. Nous avons aussi découvert que cette influence non-additive peut être modulée in situ en ajustant le potentiel chimique du graphène, sans nécessiter de changements dans la géométrie ou les matériaux du système [2]. Après cela, nous avons exploré la CLF en dehors de l'équilibre thermique entre deux couches de graphène à deux températures différentes dans un bain thermique à une troisième température [3]. Contrairement au cas usuel, où la force est toujours attractive dans des conditions d'équilibre, notre étude montre que la force peut être ajustée pour devenir répulsive si l'environnement est à basse température. Nous montrons également que pour obtenir des variations significatives de la CLF, il est essentiel de maintenir une basse température pour les feuilles de graphène, qu'elles soient en équilibre ou hors équilibre thermique. Enfin, nous constatons que la dépendance de la CLF hors équilibre en fonction du potentiel chimique devient non monotone dans une certaine plage de distances. Les différentes approches théoriques et méthodes numériques développées dans cette thèse nous permettrons, dans un futur très proche, d'explorer d'autres situations intéressantes comme le transfert de chaleur et la CLF hors équilibre thermique entre deux réseaux de graphène, la CLF entre un cylindre diélectrique couvert partiellement de graphène et un plan, ou encore le torque de Casimir dans différentes nano-structures à base de graphène.

[1] Youssef Jeyar, Mauro Antezza, and Brahim Guizal. Physical Review E, 107(2):025306, 2023.

[2] Youssef Jeyar,  Minggang Luo, Kevin Austry, Brahim Guizal, Yi Zheng, H. B. Chan, and Mauro Antezza. arXiv:2306.17640, 2023

[3] Youssef Jeyar, Kevin Austry, Minggang Luo, Brahim Guizal, H. B. Chan, and Mauro Antezza. Physical Review B, 108,115412, 2023.

The paper presents systematic study on stability of the ATPS composed of mixtures of incompatible polymers (polyethylene glycol and dextran), stabilized by nanogel particles of bovine milk protein (β-lactoglobulin –BLG), further referred as (PEG(Mw)-in-DEX(Mw))BLG, where Mw is molecular mass of polymer used in our studies. The Mw of PEG was changed in the range 10-20kDa, while DEX in the range 20-75kDa. Four different blend solutions with different Mw of each polymer were prepared. Firstly, a comprehensive characterization of the investigated systems was carried out, including density as well as viscosity measurements, before and after mixing. In addition, in situ imaging was conducted using confocal microscopy, and interfacial tensions were examined using SDT (Spinning Drop Tensiometer).
After analyzing stability of several systems , a new relationship related to the molecular weight of polymers in terms of ATPS stability was revealed. It was found that with increasing the difference between molecular weight of polymer forming the continuous and dispersed phases, the stability of the protein-stabilized systems was increasing, as well. This effect resulting from changes in polymer molecular weights in presence of BLG nanogels particles led to spectacular extension of the emulsion stability.
Furthermore, it was found that the nanogel particles size, adjusted by proper synthesis conditions (mainly pH of native BLG solution before synthesis), strongly affects the ATPS stability which reaches its optimum for the BLG particles diameter ranging between 50 and 80 nm (pH of BLG native solution 5,9-6,1) (Fig. 1., BLG concentration equal to 0,105 % w/w). It was found, moreover that too large and too small nanoparticles did not stabilize the system effectively, what should be associated to BLG size-dependent ability of accumulation inside the interfacial region (between PEG and DEX rich phases).

Active matter is a broad class of materials within which individual entities, the active particles, consume energy in order to perform movement. These materials are at the intersection of many distinct fields of research, such as biology, engineering, and physics, and have thus attracted considerable attention. Because of their perpetual consumption of energy, these systems are out of thermodynamic equilibrium. As a consequence they display a wealth of surprising phenomena which challenge our conception of equilibrium phases and dynamics. Among them, collective motion is particularly intriguing and exciting on multiple grounds. First because it emerges in systems with distinct length and time scales, from collections of cells to large crowds, flocks, and swarms, yet with some common characteristics. This thus suggests some sense of universality in the mechanisms leading to different collective behaviours. Second because parts of these motions display signatures shared with other equilibrium phenomena. While the latter are very diverse, ranging from the glass transition to inertial turbulence, these connections mean that a number of concepts and tools are readily available to describe out-of-equilibrium behaviours. Third because the possible applications of the understanding and control of these phenomena are far-reaching: treatment of specific pathologies, design of intelligent materials, crowd management, etc. In this Thesis, we focus on dense active matter, where the movement of individual particles is hindered by crowding effects, and aim to characterise how this competition leads to emerging collective motion. To this effect we use a simple model of two-dimensional isotropic self-propelled particles, namely active Ornstein-Uhlenbeck particles, where the departure from the equilibrium limit is controlled via the persistence time of propulsion forces. Owing to its simplicity, the phenomena described within this model have the potential to apply to a broad range of materials. We broadly map the phase behaviour of this model, from the equilibrium-like regime at small persistence to the to far-from-equilibrium regime at large persistence. We focus our efforts on the latter regime, where velocity correlations were recently shown to emerge. We demonstrate that a disordered liquid phase exists up to very large persistence, if polydispersity frustrates the ordering of the system, and that this persistent liquid displays various manifestations of disordered collective motion. First, we show that persistent systems are dynamically arrested at large packing fraction. Close to dynamical arrest, we find that the liquid displays dynamical heterogeneity similar to equilibrium dense systems. We investigate, in the idealised limit of infinite persistence, the microscopic processes leading to these heterogeneities. Then, away from dynamical arrest, we show that our model displays chaotic advection flows, as typically shown by turbulent systems. We highlight how this specific behaviour may be universal to a broader class of active systems relying on the competition of crowding and persistent forcing. Finally, in monodisperse systems which display long-range order at large packing fraction, we describe the far-from-equilibrium mechanisms leading to structural relaxation.

Abstract:

Although water is one of the most widespread material on the earth's surface and the most directly involved in a large number of phenomena, both natural and man-made; and although its molecule is made up of just 3 atoms, it still conceals many mysteries. Not all its physical and chemical properties are yet fully understood, especially when it is confined to nanometric spaces. It is therefore still the subject of in-depth fundamental studies. However, the many technical difficulties encountered when working at the nanometric scale mean that today, most published studies are theoretical rather than experimental. The need to collect experimental data is therefore essential, particularly from systems constituted of individual nano-objects. This is the general framework for the experimental research reported in this thesis. The work carried out can be divided into two distinct parts, each of which aims to contribute to the current and future experimental studies which will be carried out on water confined in a single nanopore.

The first part of the project involves the development of an experimental protocol for fabricating micro-platforms that are impervious to liquid water, water vapor and vacuum. The fabrication of these microsystems is based on micro photolithography techniques and the use of SU-8 resin. We show that it is possible to produce waterproof and vacuum-tight microsystems with SU-8 walls no thicker than 35 µm. The proposed protocol is therefore perfectly suited to the realization of Lab-on-Chip/nanofluidic micro-platforms dedicated to the study of water confined in a nanopore and to water nanofluidic.

The second part reports on a study of the impact of water on the electron transport of µ-field-effect transistors made of an individual single-walled carbon nanotube (SWCNT-FET). Microelectronics techniques to design and manufacture a µ-platform consisting of several microelectrodes in contact with a single nanotube are used. These electrodes made it possible either to carry out electrical measurements or to use the Joule effect to open the nanotube at specific points and also to heat it to temperatures high enough to eliminate all traces of water from its environment. The electron transport response of the SWCNT-FET as a function of the environment around the nanotube, i.e. liquid water, ambient air, and vacuum is analyzed. A comparison is made between the responses obtained when the nanotube is closed or open. It is thus possible to propose a simplified qualitative model of interaction with water and to distinguish the impact created by water adsorbed outside the tube from that associated with water confined within the tube. This pioneering work opens up many new prospects on water in the fields of nanofluidic and fundamental studies about its structure and the dynamics of its molecules in a confined environment. First and foremost, it will be used to develop a µ-measurement platform based on the electromechanical characteristics of a single carbon nanotube in the presence of water either solid, liquid or vapour.