The question of the typical structure of nano-objects (nanoparticles, aggregates, fibers, discs, chains, ….) is recurrent in our research, and small-angle scattering of neutrons and X-rays are prominent techniques to answer it. The first part of this presentation will be devoted to a (hopefully) didactical introduction to scattering: how the technique works in practice, and what one can get out of it. In the second part, a few applications in polymer nanocomposites will be discussed. Rubber-based nanocomposites prepared by solid-phase mixing with precipitated silica nanoparticles are typically strongly aggregated systems with different levels of spatial organization, as highlighted by our group in the past [1,2]. The strategy that we developed was to investigate such systems based on the study of simplified industrial samples with ingredients limited to a strict minimum. The analysis of small-angle X-ray scattering data can then be performed on the scale of a micrometric simulation box. Tens of thousands of “model” nanoparticles are embedded in the matrix, and their dispersion strongly affects both the mechanical properties of the material, and the scattered intensity. A statistical method based on a reverse Monte Carlo solution of this many-parameter scattering problem will be presented, showing that some key features like percolation can be described [3]. Another key feature of rubber nanocomposites refers to the influence of the filler surfaces on the polymer structure and dynamics, and some recent progress will be highlighted [4]. In particular, we have studied blends of short and long chains, where one chain type is deuterated, by small-angle neutron scattering. Different degrees of spatial segregation could be identified recently, including a peculiar, “fish-shaped” interfacial gradient characterized also by reverse Monte Carlo simulations, this time of the interface. References [1] Guilhem P. Baeza, Anne-Caroline Genix, C. Degrandcourt, Laurent Petitjean, Jérémie Gummel, Marc Couty, Julian Oberdisse, Macromolecules 2013, 46, 317−329 (cover article) [2] A.C. Genix and J. Oberdisse, Current Opinion in Colloid and Interface Science, 2015, 20 (4), 293-303 [3] Musino D, Genix A-C, Chauveau E, Bizien T, Oberdisse J, Nanoscale 2020, 12:3907. [4] A.C. Genix, V. Bocharova, B. Carroll, P. Dieudonné-George, M. Sztucki, R. Schweins, A. P. Sokolov, and J. Oberdisse, ACS Applied Materials and Interfaces, 2021, 11 (19), 17863-17872

Small-angle neutron scattering is the perfect tool to study the average conformation of macromolecules in about any environment, from solvents to other polymer molecules. The power of the method is intimately related to the length scale of observation, the virtual absence of artefacts due to the averaging, and most importantly, the possibilities to adjust contrasts and highlight chosen parts of the samples. In this talk, some recent applications will be reviewed. During a stay with Arantxa Arbe and Juan Colmenero (San Sebastian), we have studied the structure of synthetic single-chain nanoparticles (SCNPs) in presence of linear polystyrene crowding molecules under contrast-matching of the crowders [1]. A model describing the scattering of aggregating polydisperse SCNPs has been developed, resulting in the determination of the potentially squeezed size of the individual SCNPs within aggregates, their local chain statistics, and the average aggregation number, as a function of crowding. Secondly, in collaboration with Marian Cors and Thomas Hellweg (Bielefeld), we have investigated the internal structure of core-shell microgel particles in suspension. Using selective deuteration, core- and shell monomers could be measured independently, and the corresponding monomer profile described by a reverse Monte Carlo approach [2]. In the last part, an application to polymer nanocomposites will be discussed. Rubber-based nanocomposites show a large variety of spatial organization of the filler nanoparticles, which can be studied by small-angle scattering, and analyzed by large-scale reverse Monte Carole simulation [3]. A key feature of rubber nanocomposites is linked to the influence of the filler surfaces on the polymer structure and dynamics, [4]. In particular, we have studied blends of short and long chains, where one chain type is deuterated, by small-angle neutron scattering. Different degrees of spatial segregation could be identified, including a peculiar, “fish-shaped” interfacial gradient. [1] J. Oberdisse, M. González-Burgos, A. Mendia, A. Arbe, A. J. Moreno, J. A. Pomposo, A. Radulescu and J. Colmenero, Macromolecules, 2019, 4295.[2] M. Cors, O. Wrede, L. Wiehemeier, A. Feoktystov, F. Cousin, T. Hellweg, J. Oberdisse, Scientific Reports 2019, 9, 13812.[3] D. Musino, A.-C. Genix, T. Bizien, J. Oberdisse, Nanoscale, 2020, 12, 3907.[4] A.C. Genix, V. Bocharova, B. Carroll, P. Dieudonné-George, M. Sztucki, R. Schweins, A. P. Sokolov, and J. Oberdisse, ACS Applied Materials and Interfaces 2021, 13, 36262.

A few examples of experimental studies of soft matter systems will be presented toillustrate some aspects of the personal and scientific journey of Isabelle Grillo. I have metIsabelle for the first time almost twenty-five years ago in the Bombannes school, and sincethen a combination of geographic coincidence, common scientific topics – from surfactantsystems to polymer nanocomposites -, and a shared interest in a technique, neutronscattering, made us walk some steps of this journey together. While the extra-ordinarystructure of many of the systems Isabelle took interest in will be presented by world-leadingexperts in this symposium, my presentation will shortly highlight vesicular structures, andthen bridge the gap between PhD work supervised by us on nanocomposites to our currentunderstanding of the structure of such nanomaterials.

The structure of the nematic (cholesteric) drops that form at the clearing temperature of a mixture of the bent-core molecule CB7CB and the rod-like molecule 8CB doped with a surfactant is optically determined. Using experimental observations and numerical simulations, it is demonstrated that the director field inside these drops is not escaped-concentric as previously proposed, but twisted-bipolar. The Lehmann rotation of these drops in the presence of a temperature gradient is described. Their rotation velocity is shown to be proportional to the temperature gradient and to the surface twist angle of the director field and inversely proportional to the drop radius, thus revealing a fundamental scaling law for the Lehmann effect of nematic/cholesteric twisted bipolar droplets.

Poly(N-isopropylacrylamide)-based microgels are soft colloids undergoing a Volume Phase Transition (VPT) close to ambient temperature. Although widely employed for fundamental research and application purposes, the modifications of the microgel internal structure occurring at the VPT are not yet completely understood, especially concerning the role of electrostatics. Here we study in detail, both experimentally and numerically, the effect of the addition of acrylic acid (AAc) co-monomer on the microgel deswelling process. By combining viscosimetry, light scattering and electrophoresis, we show that the progressive addition of AAc increases the microgel mass and suppresses

Background: Chronic Obstructive Pulmonary Disease (COPD), a major cause of mortality and disability, is a complex disease with heterogeneous and ill-understood biological mechanisms. Human induced pluripotent stem cells (hiPSCs) are a promising tool to model human disease, including the impact of genetic susceptibility. Methods: We developed a simple and reliable method for reprogramming peripheral blood mononuclear cells into hiPSCs and to differentiate them into air–liquid interface bronchial epithelium within 45 days. Importantly, this method does not involve any cell sorting step. We reprogrammed blood cells from one healthy control and three patients with very severe COPD. Results: The mean cell purity at the definitive endoderm and ventral anterior foregut endoderm (vAFE) stages was >80%, assessed by quantifying C-X-C Motif Chemokine Receptor 4/SRY-Box Transcription Factor 17 (CXCR4/SOX17) and NK2 Homeobox 1 (NKX2.1) expression, respectively. vAFE cells from all four hiPSC lines differentiated into bronchial epithelium in air–liquid interface conditions, with large zones covered by beating ciliated, basal, goblets, club cells and neuroendocrine cells, as found in vivo. The hiPSC-derived airway epithelium (iALI) from patients with very severe COPD and from the healthy control were undistinguishable. Conclusions: iALI bronchial epithelium is ready for better understanding lung disease pathogenesis and accelerating drug discovery.

Understanding the origin of the unique rheological properties of wheat gluten, the protein fraction of wheat grain, is crucial in bread-making processes and has raised questions of scientists for decades. Gluten is a complex mixture of two families of proteins, monomeric gliadins and polymeric glutenins. To better understand the respective role of the different classes of proteins in the supramolecular structure of gluten and its link to the material properties, we investigate here concentrated dispersions of gluten proteins in water with a fixed total protein concentration but variable composition in gliadin and glutenin. Linear viscoelasticity measurements show a gradual increase in the viscosity of the samples as the glutenin mass content increases from 7 to 66%. While the gliadin-rich samples are microphase-separated viscous fluids, homogeneous and transparent pre-gel and gels are obtained with the replacement of gliadin by glutenin. To unravel the flow properties of the gluten samples, we perform shear startup experiments at different shear-rates. In accordance with the linear viscoelastic signature, three classes of behavior are evidenced depending on the protein composition. As samples get depleted in gliadin and enriched in glutenin, distinctive features are measured: (i) viscosity undershoot suggesting droplet elongation for microphase-separated dispersions, (ii) stress overshoot and partial structural relaxation for near-critical pre-gels, and (iii) strain hardening and flow instabilities of gels. We discuss the experimental results by analogy with the behavior of model systems, including viscoelastic emulsions, branched polymer melts, and critical gels, and provide a consistent physical picture of the supramolecular features of the three classes of protein dispersions.