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Even in the absence of surfactants, polymers, or particles, spontaneous emulsions produced by dilution with water can be stable over days. This “Ouzo effect” used by the industry is obtained by rapid dilution from an identified “pre-Ouzo” domain of composition where weak aggregates are present: nanometer-sized clusters covered by a surface layer enriched in a hydrotrope such as ethanol. In these systems, Ostwald ripening is not an effective destabilizing mechanism. Using in situ autodilution small-angle X-ray scattering (SAXS), we follow the morphological transitions occurring in a ternary mixture of water/n-octanol/ethanol throughout the monophasic and biphasic regions. This allows for the first time an online characterization of the multiscale coexisting microstructures. Small-angle neutron scattering (SANS) profiles on metastable emulsions as well as phase-separated samples complete the SAXS data, taking advantage of contrast variation via isotopic substitution. After crossing the phase boundary into the two-phase region, coexisting phases are both ternary solutions structured at the nanometer scale when the emulsion is stable. The transition from single phase to two phases is asymmetric around the plait point. When the initial concentration of the hydrotrope is below the minimum hydrotrope concentration (MHC), emulsification failure occurs, i.e., emulsions cream within seconds. Beyond MHC, the low interfacial tension between coexisting ternary fluids results in a Laplace pressure below 100 Pa, explaining the puzzling resilience of spontaneous emulsion to the universal mechanism of Ostwald ripening.

We propose in this article a concept called "augmented 3D printing with molecular modeling" as an application framework. Visualization is an essential means to represent complex biochemical and biological objects in order to understand their structures as functions. By pairing augmented reality systems and 3D printing, we propose to design a new collaborative molecular graphics tool (under implementation) for scientific visualization and visual analytics. The printed object is then used as a support for the visual augmentation by allowing the superimposition of different visualizations. Thus, still aware of his environment, the user can easily communicate with his collaborators while moving around the object. This user-friendly tool, dedicated to non-initiated scientists, will facilitate the dissemination of knowledge and collaboration between interdisciplinary researchers. Here, we present a first prototype and we focus on the main molecule tracking component. Initial feedback from our users suggests that our proposal is valid, and shows a real interest in this type of tool, with an intuitive interface., Workshop on Molecular Graphics and Visual Analysis of Molecular Data, Session 1, 1, 5, Mathieu Noizet, Valentine Peltier, Hervé Deleau, Manuel Dauchez, Stéphanie Prévost, and Jessica Jonquet-Prevoteau, CCS Concepts: Computing methodologies --> Modeling methodologies; Mixed / augmented reality; Scientific visualization; Humancentered computing --> Graphical user interfaces

Enseigner l’accord du participe passé pose des problèmes spécifiques du fait de ses caractéristiques empruntant à la fois au verbe et à l’adjectif. La tradition scolaire française traite cette difficulté en formulant des règles d’accord utilisant un vocabulaire grammatical assez étendu. Nous exploitons 178 dictées et 65 entretiens métagraphiques recueillis auprès d’élèves de l’enseignement supérieur technique français afin d’observer leur traitement de formes de participe passé et leur utilisation, à cette fin, du vocabulaire métalinguistique scolaire. Il apparait que ces formes sont abondamment commentées parce qu’elles constituent des difficultés pour les locuteurs. Une grande partie d’entre eux mobilise le vocabulaire grammatical repéré dans les manuels scolaires. Mais les notions de sujet et de COD leur posent problème. À deux exceptions près, quand la notion de COD est mobilisée, elle constitue un obstacle et non une aide. Le terme sujet est davantage associé à des procédures efficaces mais il est utilisé de façon récurrente pour désigner le donneur d’accord, qu’il s’agisse du sujet syntaxique ou non.

This work presents well-defined and switchable micelles of block copolymers consisting of the two anionic polyelectrolytes sodium polyacrylate (NaPA) and sodium polystyrene sulfonate (NaPSS). Micellization occurs due to the specific binding of Ca2+ to acrylate groups, which results in neutralization of the corresponding block and thereby formation of the hydrophobic core of the micelles. In contrast, the PSS block remains charged and forms the stabilizing shell. Micellization is triggered by variations of the Ca2+ concentration or the temperature and is a fully reversible and repeatable process. Small-angle neutron scattering (SANS) could unambiguously reveal the structure of the micelles, using a partially deuterated polymer and the contrast variation technique. Considering the variety of metal cations and their broad spectrum of interactions with polyelectrolytes, this new class of like-charged block copolymers opens the door to a broad range of switchable and responsive polyelectrolyte-based systems.

Refractive index matched particles serve as essential model systems for colloid scientists, providing nearly hard spheres to explore structure and dynamics. The poly(methyl methacrylate) latexes typically used are often refractive index matched by dispersing them in binary solvent mixtures, but this can lead to undesirable changes, such as particle charging or swelling. To avoid these shortcomings, we have synthesized refractive index matched colloids using polymerization-induced self-assembly (PISA) rather than as polymer latexes. The crucial difference is that these diblock copolymer nanoparticles consist of a single core-forming polymer in a single non-ionizable solvent. The diblock copolymer chosen was poly(stearyl methacrylate)–poly(2,2,2-trifluoroethyl methacrylate) (PSMA–PTFEMA), which self-assembles to form PTFEMA core spheres in n-alkanes. By monitoring scattered light intensity, n-tetradecane was found to be the optimal solvent for matching the refractive index of such nanoparticles. As expected for PISA syntheses, the diameter of the colloids can be controlled by varying the PTFEMA degree of polymerization. Concentrated dispersions were prepared, and the diffusion of the PSMA–PTFEMA nanoparticles as a function of volume fraction was measured. These diblock copolymer nanoparticles are a promising new system of transparent spheres for future colloidal studies.

Aqueous solutions of a nonionic surfactant (either Tween20 or BrijL23) and an anionic surfactant (sodium dodecyl sulfate, SDS) are investigated, using small-angle neutron scattering (SANS). SANS spectra are analysed by using a core-shell model to describe the form factor of self-assembled surfactant micelles; the intermicellar interactions are modelled by using a hard-sphere Percus–Yevick (HS-PY) or a rescaled mean spherical approximation (RMSA) structure factor. Choosing these specific nonionic surfactants allows for comparison of the effect of branched (Tween20) and linear (BrijL23) surfactant headgroups, both constituted of poly-ethylene oxide (PEO) groups. The nonionic–anionic surfactant mixtures are studied at various concentrations up to highly concentrated samples (ϕ ≲ 0.45) and various mixing ratios, from pure nonionic to pure anionic surfactant solutions. The scattering data reveal the formation of mixed micelles already at concentrations below the critical micelle concentration of SDS. At higher volume fractions, excluded volume effects dominate the intermicellar structuring, even for charged micelles. In consequence, at high volume fractions, the intermicellar structuring is the same for charged and uncharged micelles. At all mixing ratios, almost spherical mixed micelles form. This offers the opportunity to create a system of colloidal particles with a variable surface charge. This excludes only roughly equimolar mixing ratios (X≈ 0.4–0.6) at which the micelles significantly increase in size and ellipticity due to specific sulfate–EO interactions.