Edouard Chauveau

Satureja montana essential oil is a natural substance able to inhibit the growth of several pathogens. This antimicrobial effect is often attributed to its ability to penetrate cellular structures and disrupt them. Although these properties are recognized as playing a key role in the mechanism of action of this substance, many unresolved issues still exist, and fundamental studies focused on such aspects are scarce. In this framework, we investigated the interaction of SEO with lipid monolayers, which represent simplified models of cell membranes, using the Langmuir monolayer technique, complemented by fluorescence anisotropy and differential scanning calorimetry on lipid bilayers. By focusing on packing conditions that approximate those of biological membranes and using lipids with different polar heads and structures, such as the ones occurring in bacterial membranes, we aim to clarify the effect of this essential oil on the lipid membrane. Our results show that Satureja montana essential oil consistently manages to insert into the membrane and interfere with the lipid–lipid interactions, thereby altering the lipid packing and significantly increasing the membrane fluidity, depending on the oil concentration and the nature of the lipid.

Two-dimensional Dirac fermions in HgTe quantum wells close to the topological phase transition can generate significant cyclotron emission that is magnetic field tunable in the terahertz frequency range. Due to their relativistic-like dynamics, their cyclotron mass is strongly dependent on their electron concentration in the quantum well, providing a second tunability lever and paving the way for a gate-tunable, permanent-magnet Landau laser. In this work, we demonstrate the proof-of-concept of such a back-gate tunable THz cyclotron emitter at a fixed magnetic field. The emission frequency detected at 1.5 T is centered at 2.2 THz and can already be electrically tuned over 250 GHz. With an optimized gate and a realistic permanent magnet of 1.0 T, we estimate that the cyclotron emission could be continuously and rapidly tunable by the gate bias between 1 and 3 THz, that is to say on the less covered part of the THz gap.

Some original poly(tetrasubstituted imidazole)s incorporating different units were synthesized and characterized. These materials were obtained via a cascade polycondensation process assisted by microwave irradiation that was developed by our team. This time, we integrated two well-known chromophore structures into the macromolecular backbone, which were benzothiadiazole (BTD) and diketopyrrolopyrrole (DKPP). These new polymers were fully characterized: their chemical structures were confirmed using NMR spectroscopy and their thermal, optical and electrochemical properties were investigated and compared with a reference polymer containing a phenyl spacer instead of the mentioned chromophore units. These materials were found to exhibit a large Stokes shift of up to 350 nm. Furthermore, a polymer presenting large absorption on the UV–visible range and an emission close to the near-infrared region was obtained by coupling the mentioned moieties. According to the established properties of this latter polymer, it presents a potential for applications in biological imaging or optoelectronic devices.

Both the dispersion state of nanoparticles (NPs) within polymer nanocomposites (PNCs) and the dynamical state of the polymer altered by the presence of the NP/polymer interfaces have a strong impact on the macroscopic properties of PNCs. In particular, mechanical properties are strongly affected by percolation of hard phases, which may be NP networks, dynamically modified polymer regions, or combinations of both. In this article, the impact on dispersion and dynamics of surface modification of the NPs by short monomethoxysilanes with eight carbons in the alkyl part (C₈) is studied. As a function of grafting density and particle content, polymer dynamics is followed by broadband dielectric spectroscopy and analyzed by an interfacial layer model, whereas the particle dispersion is investigated by small-angle X-ray scattering and analyzed by reverse Monte Carlo simulations. NP dispersions are found to be destabilized only at the highest grafting. The interfacial layer formalism allows the clear identification of the volume fraction of interfacial polymer, with its characteristic time. The strongest dynamical slow-down in the polymer is found for unmodified NPs, while grafting weakens this effect progressively. The combination of all three techniques enables a unique measurement of the true thickness of the interfacial layer, which is ca. 5 nm. Finally, the comparison between longer (C₁₈) and shorter (C₈) grafts provides unprecedented insight into the efficacy and tunability of surface modification. It is shown that C₈-grafting allows for a more progressive tuning, which goes beyond a pure mass effect.

PNIPAm microgels synthesized via free radical polymerization (FRP) are often considered as neutral colloids in aqueous media, although it is well known, since the pioneering works of Pelton and coworkers, that the vanishing electrophoretic mobility characterizing swollen microgels largely increases above the lower critical solution temperature (LCST) of PNIPAm, at which microgels partially collapse. The presence of an electric charge has been attributed to the ionic initiators that are employed when FRP is performed in water and that stay anchored to microgel particles. Combining dynamic light scattering (DLS), electrophoresis, transmission electron microscopy (TEM) and atomic force microscopy (AFM) experiments, we show that collapsed ionic PNIPAm microgels undergo large mobility reversal and reentrant condensation when they are co-suspended with oppositely charged polyelectrolytes (PE) or nanoparticles (NP), while their stability remains unaffected by PE or NP addition at lower temperatures, where microgels are swollen and their charge density is low. Our results highlight a somehow double-faced electrostatic behavior of PNIPAm microgels due to their tunable charge density: they behave as quasi-neutral colloids at temperature below LCST, while they strongly interact with oppositely charged species when they are in their collapsed state. The very similar phenomenology encountered when microgels are surrounded by polylysine chains and silica nanoparticles points to the general character of this twofold behavior of PNIPAm-based colloids in water.

Nematic twist-bend phases (N_TB) are new types of nematic liquid crystalline phases with attractive properties for future electro-optic applications. However, most of these states are monotropic or are stable only in a narrow high temperature range. They are often destabilized under moderate cooling, and only a few single compounds have shown to give room temperature N_TB phases. Mixtures of twist-bend nematic liquid crystals with simple nematogens have shown to strongly lower the nematic to N_TB phase transition temperature. Here, we examined the behaviour of new types of mixtures with the dimeric liquid crystal [4′,4′-(heptane-1,7-diyl)bis(([1′,1″-biphenyl]4″-carbo-nitrile))] (CB7CB). This now well-known twist-bend nematic liquid crystal presents a nematic twist-bend phase below T ≈ 104 °C. Mixtures with other monomeric alkyl or alkoxy -biphenylcarbonitriles liquid crystals that display a smectic A (SmA) phase also strongly reduce this temperature. The most interesting smectogen is 4′-Octyl-4-biphenylcarbonitrile (8CB), for which a long-term metastable N_TB phase is found at room and lower temperatures. This paper presents the complete phase diagram of the corresponding binary system and a detailed investigation of its thermal, optical, dielectric, and elastic properties.