Metallurgy of soft spheres with hard core: from BCC to Frank-Kasper phases

Understanding how soft particles can fill the space is still an open question. Structures far from classical FCC or BCC phases are now commonly experimentally observed in many different systems. Models based on pair interaction between soft particle are at present much studied in 2D. Pair interaction with two different lengths have been shown to lead to quasicrystalline architectures. It is also the case for a hard core with a square repulsive shoulder potential. In 3D, global approaches have been proposed for instance by minimizing the interface area between the deformed objects in the case of foams or micellar systems or using self-consistent mean field theory in copolymer melts. In this paper we propose to compare a strong van der Waals attraction between spherical hard cores and an elastic energy associated to the deformation of the soft corona. This deformation is measured as the shift between the deformed shell compared to a corona with a perfect spherical symmetry. The two main parameters in this model are: the hard core volume fraction and the weight of the elastic energy compared to the van der Waals one. The elastic energy clearly favours the BCC structure but large van der Waals forces favors Frank and Kasper phases. This result opens a route towards controlling the building of nanoparticle superlattices with complex structures and thus original physical properties.Comment: To appear in EPJ

Grazing incidence x-ray diffraction studies of lipid-peptide mixed monolayers during shear flow

Grazing Incidence X-ray Diffraction (GIXD) studies of monolayers of biomolecules at the air-water interface give quantitative information of in-plane packing, coherence lengths of the ordered diffracting crystalline domains and the orientation of hydrocarbon chains. Rheo-GIXD measurements revel quantitative changes in the monolayer under shear. Here we report GIXD studies of monolayers of Alamethicin peptide, DPPC lipid and their mixtures at the air-water interface under the application of steady shear stresses. The Alamethicin monolayer and the mixed monolayer show flow jamming transition. On the other hand, pure DPPC monolayer under the constant stress flows steadily with a notable enhancement of area/molecule, coherence length, and the tilt angle with increasing stress, suggesting fusion of nanocrystallites during flow. The DPPC-Alamethicin mixed monolayer shows no significant change in the area/DPPC molecule or in the DPPC chain tilt but the coherence length of both phases (DPPC and Alamethicin) increases suggesting that the crystallites of individual phases are merging to bigger size promoting more separation of phases in the system during flow. Our results show that Rheo-GIXD has the potential to explore in-situ molecular structural changes under rheological conditions for a diverse range of confined biomolecules at the interfaces.Comment: 21 pages, 11 figures, 2 table

COVID-19 symptoms at hospital admission vary with age and sex: results from the ISARIC prospective multinational observational study

Background: The ISARIC prospective multinational observational study is the largest cohort of hospitalized patients with COVID-19. We present relationships of age, sex, and nationality to presenting symptoms. Methods: International, prospective observational study of 60 109 hospitalized symptomatic patients with laboratory-confirmed COVID-19 recruited from 43 countries between 30 January and 3 August 2020. Logistic regression was performed to evaluate relationships of age and sex to published COVID-19 case definitions and the most commonly reported symptoms. Results: ‘Typical’ symptoms of fever (69%), cough (68%) and shortness of breath (66%) were the most commonly reported. 92% of patients experienced at least one of these. Prevalence of typical symptoms was greatest in 30- to 60-year-olds (respectively 80, 79, 69%; at least one 95%). They were reported less frequently in children (≤ 18 years: 69, 48, 23; 85%), older adults (≥ 70 years: 61, 62, 65; 90%), and women (66, 66, 64; 90%; vs. men 71, 70, 67; 93%, each P < 0.001). The most common atypical presentations under 60 years of age were nausea and vomiting and abdominal pain, and over 60 years was confusion. Regression models showed significant differences in symptoms with sex, age and country. Interpretation: This international collaboration has allowed us to report reliable symptom data from the largest cohort of patients admitted to hospital with COVID-19. Adults over 60 and children admitted to hospital with COVID-19 are less likely to present with typical symptoms. Nausea and vomiting are common atypical presentations under 30 years. Confusion is a frequent atypical presentation of COVID-19 in adults over 60 years. Women are less likely to experience typical symptoms than men

Structures et proprietes optiques des cristaux colloiedaux minces

SIGLECNRS T 56026 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

ETUDE STRUCTURALE DES PHASES BLEUES SMECTIQUES

PARIS7-Bibliothèque centrale (751132105) / SudocSudocFranceF

Phases lamellaires dopées avec des polyoxométalates

Les systèmes hybrides organiques-inorganiques sont actuellement l'objet d'une grande attention parce qu'ils peuvent combiner les propriétés électroniques des matériaux inorganiques avec les propriétés d'autoassemblage des molécules organiques. Nous avons formulé un tel système, en associant des nanoparticules de polyoxométallates (POMs) avec une phase lamellaire Iyotrope. La diffusion de rayons X et la microscopie en lumière polarisée ont démontré que ce système hybride, très chargé en POMs, est un nanocomposite de structure lamellaire cristal-liquide (La), avec des propriétés viscoélastiques proches de celles des gels. L'interprétation des données de rayons X suggère fortement que les POMs sont localisés près des groupements -OH terminaux du tensio-actif, dans la couche aqueuse. De plus, le système présente du photochromisme réversible, associé à la photoréduction de l'anion polyoxométallate. D'un point de vue plus fondamental, ces matériaux hybrides peuvent servir comme modèles pour étudier les propriétés statiques et dynamiques des nanoparticules confinées dans des phases lamellaires. Ainsi, la diffusion de rayons X a été utilisée pour étudier l'effet du confinement sur le potentiel d'interaction entre les particules. En outre, nous avons mesuré les coefficients de diffusion des particules, en utilisant la RMN en gradient de champ. Nous avons démontré que le coefficient de diffusion est très réduit dans la phase, ce qui confirme la forte interaction entre les particules et la bicouche. Finalement, des expériences simples ont permis l'étude des propriétés rhéologiques du système.Organic-inorganic hybrid systems have recently attracted a lot of attention. They can potentially combine the electronic properties of inorganic materials with the self-assembly properties of organic molecules. We have developed such a hybrid system, in which polyoxometallate nanoparticles (POMs) are inserted between the bilayers of a Iyotropic lamellar phase. X-ray scattering and polarized light microscopy demonstrate that these hybrid materials, highly loaded with POMs, are nanocomposites of liquid-crystalline lamellar structure (La), with viscoelastic properties reminiscent of those of gels. The interpretation of X-ray scattering data strongly suggests that the POMs are located close to the terminal -OH groups of the nonionic surfactants, within the aqueous sublayers. Moreover, these materials exhibit a reversible photochromism associated to the photoreduction of the polyoxometallate anion. From a more fundamental point ofview, these hybrid materials can serve as models for the study ofboth static and dynamic properties of nanoparticles confined within soft lamellar structures. X-ray scattering was used to study the effect of confinement on the interparticle interaction potential. Furthermore, pulsed-field gradient NMR was used to measure the translational diffusion coefficients of the POMs as a function of the inter-bilayer distance. It was demonstrated that the dynamics of the particles are significantly slowed down, and, thus, that they strongly interact with the bilayer. Finally, sorne simple experiments were done to determine the rheological behaviour of the system in question.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

Evidence for a C14 Frank-Kasper Phase in One-Size Gold Nanoparticle Superlattices

International audienceThe Frank-Kasper phases were already known in 1982 when quasicrystals have been discovered but their complex architectures are now considered as making a link between simple close-packed periodic structures and some quasiperiodic ones. These tetrahedrally close packed structures are observed in many materials from elements to intermetallics as well as self-assembled soft materials like micellar systems, den-dritric liquid crystals, star polymers and more recently block-copolymers or heated gold nanocrystal superlattices. We report here the existence of a Frank-Kasper phase with hexagonal symmetry (MgZn 2 type, also labelled C14) in superlattices of monodis-perse hydrophobically-coated gold particles at room temperature obtained from sus-pensions in various solvents. The existence of such a structure in this system is analysed in terms of geometrical parameters including gold core diameter, ligand length and grafting density and an energetic approach based on van der Waals attraction. Hydrophobically-coated gold nanoparticles is a new system that exhibit a Frank and Kasper phase built by one-size objects. This result opens a route towards nanoparticle superlattice with complex structures and thus original physical properties