As compared to other techniques of analysis of nanostructures, small-angle neutron scattering has always been way better in terms of design of special contrast situations, and worse for statistics due to inherently low flux. SANS beamlines at ILL, and in particular D11 dedicated to soft matter studies, have allowed to keep the first advantage, while providing excellent experimental conditions respect to, including with respect to flux.In this talk, I will present some recent studies of polymer structure in nanocomposites. Such materials have striking mechanical and dynamical properties, in particular the dynamics of the polymer close to the nanoparticles has triggered a large body of experimental and theoretical studies. The possible slow-down of the polymer corresponds to higher moduli, and the percolation of any hard phase, particles or slowed-down polymer, has a strong impact on the macroscopic mechanical properties. If one wishes to specifically characterize the structure of the polymer, SANS is one of the best options. By blending hydrogenated and deuterated chains, while matching the filler silica nanoparticles, we have recently provided evidence for chain-mass dependent bulk or interfacial segregation, and modelling and experimental results will be critically reviewed. In a second study, we have characterized the particle dispersion by small-angle scattering and reverse Monte Carlo modelling, and used it to improve the determination of the thickness of the polymer interfacial layer seen by broadband dielectric spectroscopy. Both the general nanoparticle dispersion and the characteristic time of this interfacial layer has been shown to be tunable by surface modification, paving the way for a precise control of mechanical properties of polymer nanocomposites in the future.

Dans le cadre du minicolloque "Neutrons et polymères".

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

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.

Gene expression consists in the synthesis of proteins from the information encoded on DNA. One of the two main steps of gene expression is the translation of messenger RNA (mRNA) into polypeptide sequences of amino acids. Here, by taking into account mRNA degradation, we model the motion of ribosomes along mRNA with a ballistic model where particles advance along a filament without excluded volume interactions. Unidirectional models of transport have previously been used to fit the average density of ribosomes obtained by the experimental ribo-sequencing (Ribo-seq) technique. In this case an inverse fit gives access to the kinetic rates: the position-dependent speeds and the entry rate of ribosomes onto mRNA. The degradation rate is not, however, accounted for and experimental data from different experiments are needed to have enough parameters for the fit. Here, we propose an entirely novel experimental setup and theoretical framework consisting in splitting the mRNAs into categories depending on the number of ribosomes from one to four. We solve analytically the ballistic model for a fixed number of ribosomes per mRNA, study the different regimes of degradation, and propose a criteria for the quality of the inverse fit. The proposed method provides a high sensitivity to the mRNA degradation rate. The additional equations coming from using the monosome (single ribosome) and polysome (arbitrary number) ribo-seq profiles enable us to determine all the kinetic rates in terms of the experimentally accessible mRNA degradation rate.