Food transition requires the replacement in human diet of animal-based proteins by alternative sources of proteins including plant-based proteins. This calls for a detailed knowledge of the functional properties of plant-based proteins, including their surface activity. In this framework, we provide here a comparative study of the interfacial properties of two plant proteins, extracted respectively from wheat and sunflower. We combine time- and concentration-dependent measurements of the surface tension and the surface rheology, as measured with a pendant-drop set-up, and of the surface excess concentration, as measured by ellipsometry, of plant protein interfacial films. We demonstrate a time-concentration superposition principle for the surface pressure and surface excess concentration, showing that the kinetics for the building of the interfacial films is essentially governed by the diffusion of the proteins from the bulk to the interface. We find that the rheological and structural properties of the interfacial protein films show markedly different behaviors for the two classes of protein, which is encoded in the structural features of the individual proteins: wheat proteins are more surface active than sunflower proteins, are keen to compress and re-arrange at an air-water interface, whereas sunflower proteins do not. This work provides qualitative and quantitative analysis of the comparative interfacial behavior of flexible and rigid plant proteins extracted respectively from wheat and sunflower, and demonstrates that a combination of several experimental techniques is necessary to obtain insightful information on the interfacial properties of any species.

Mucus is a viscoelastic aqueous fluid that participates in the protective barrier of many mammals' epithelia. In the airways, together with cilia beating, mucus rheological properties are crucial for lung mucociliary function, and, when impaired, potentially participate in the onset and progression of chronic obstructive pulmonary disease (COPD). Samples of human mucus collected in vivo are inherently contaminated and are thus poorly characterized. Human bronchial epithelium (HBE) cultures, differentiated from primary cells at an air–liquid interface, are highly reliable models to assess non-contaminated mucus. In this paper, the viscoelastic properties of HBE mucus derived from healthy subjects, patients with COPD and from smokers are measured. Hallmarks of shear-thinning and elasticity are obtained at the macroscale, whereas at the microscale mucus appears as a heterogeneous medium showing an almost Newtonian behaviour in some extended regions and an elastic behaviour close to boundaries. In addition, we developed an original method to probe mucus adhesion at the microscopic scale using optical tweezers. The measured adhesion forces and the comparison with mucus-simulants rheology as well as mucus imaging collectively support a structure composed of a network of elastic adhesive filaments with a large mesh size, embedded in a very soft gel.

Meanwhile since more than three decades smart micro-and nanogels are studied and the number of publications in this area of research is steadily growing. This year to date (May 2021) already more than 400 articles were published on this topic. In the study of such colloidal gels the most important techniques besides microscopy are scattering techniques. In the present chapter an introduction to these non-destructive techniques and their application to smart micro-and nanogels will be given, and besides some fundamental works on this topic the most recent studies in this context will be discussed. We put a focus on multi-compartment and multi-1 stimuli responsive microgels and review time-resolved small-angle scattering experiments. In addition one section is devoted to the study of crowded microgel systems.

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