Ref HAL: hal-04298384_v1
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Le fractionnement du grain de blé, qui permet la séparation de l’albumen amylacé (au cœur) de ses parties périphériques pour produire de la farine, dépend de ses propriétés mécaniques. On distingue, chez le blé tendre, des blés dits « soft », dont l’albumen est friable, et « hard » plus résistant. Ils différent par la présence de gènes codant deux protéines spécifiques, les Puroindolines (PINs) A et B, qui sont de forme sauvage (cas des soft) ou mutés (cas des hard). Ces protéines sont impliquées dans les interactions entre les constituants majeurs du grain (amidon et protéines de réserve qui entourent les granules, capables de former un réseau aux propriétés uniques appelé gluten). Nous avons pu disposer de lignées quasi-isogéniques pour la dureté qui ne différent que par la présence de ces gènes sauvages ou mutées, alors que le fond génétique est identique, et montré que ces seuls gènes affectent les caractéristiques physiques et le comportement au broyage des grains [1,2]. Nous avons pu caractériser in situ les propriétés mécaniques respectives de l’amidon et du gluten et montré leurs différences, contrairement à ce qui est établi dans la littérature, grâce au développement d’une méthode originale où la pointe d’un Microscope à Force Atomique (AFM) est utilisée pour abraser la surface de l’échantillon à analyser [3]. Nous avons également mis en évidence des différences d’interfaces entre les polymères en fonction de la dureté du grain [4]. Enfin, nous avons utilisé la méthode de caractérisation mécanique par AFM par résonance de contact (CR-AFM) pour mesurer le module d’indentation (élastique) au sein de granules d’amidon (échelle de la centaine de nanomètres), moyennant une correction originale prenant en compte la topographie locale [5]. Cette méthode a été utilisée sur des sections de grains (céréales) et graines (légumineuses) de différentes origines botaniques pour comparer les propriétés de leurs amidons.

Ref HAL: hal-04279663_v1
Ref Arxiv: 2310.16770
Ref. & Cit.: NASA ADS
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Large groups of active cilia collectively beat in a fluid medium as metachronal waves, essential for some microorganisms motility and for flow generation in mucociliary clearance. Several models can predict the emergence of metachronal waves, but what controls the properties of metachronal waves is still unclear. Here, we investigate numerically a simple model for cilia in the presence of noise on regular lattices in one- and two-dimensions. We characterize the wave using spatial correlation and the frequency of collective beating. Our results clearly show that the viscosity of the fluid medium does not affect the wavelength; the activity of the cilia does. These numerical results are supported by a dimensional analysis, which is expected to be robust against the model for active force generation, unless surrounding fluid influences the cilia activity. Interestingly, enhancement of cilia activity increases the wavelength and decreases the beating frequency, keeping the wave velocity almost unchanged. These results might have significance in understanding paramecium locomotion and mucociliary clearance diseases.

Commentaires: 6 pages, 5 figures

Ref HAL: hal-04260533_v1
DOI: 10.1088/2515-7639/ad06cc
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Soft materials are usually defined as materials made of mesoscopic entities, often self-organized, sensitive to thermal fluctuations and to weak perturbations. Archetypal examples are colloids, polymers, amphiphiles, liquid crystals, foams. The importance of soft materials in everyday commodity products, as well as in technological applications, is enormous, and controlling or improving their properties is the focus of many efforts. From a fundamental perspective, the possibility of manipulating soft material properties, by tuning interactions between constituents and by applying external perturbations, gives rise to an almost unlimited variety in physical properties. Together with the relative ease to observe and characterize them, this renders soft matter systems powerful model systems to investigate statistical physics phenomena, many of them relevant as well to hard condensed matter systems. Understanding the emerging properties from mesoscale constituents still poses enormous challenges, which have stimulated a wealth of new experimental approaches, including the synthesis of new systems with, e.g., tailored self-assembling properties, or novel experimental techniques in imaging, scattering or rheology. Theoretical and numerical methods, and coarse-grained models, have become central to predict physical properties of soft materials, while computational approaches that also use machine learning tools are playing a progressively major role in many investigations. This roadmap paper intends to give a broad overview of recent and possible future activities in the field of soft materials, with experts covering various developments and challenges in material synthesis and characterization, instrumental, simulation and theoretical methods as well as general concepts.

Ref HAL: hal-04244864_v1
Ref Arxiv: 2310.14682
DOI: 10.1140/epje/s10189-023-00306-6
Ref. & Cit.: NASA ADS
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Small-angle scattering is a commonly used tool to analyze the dispersion of nanoparticles in all kinds of matrices. Besides some obvious cases, the associated structure factor is often complex and cannot be reduced to a simple interparticle interaction, like excluded volume only. In recent experiments, we have encountered a surprising absence of structure factors (S(q) = 1) in scattering from rather concentrated polymer nanocomposites [A.-C. Genix et al, ACS Appl. Mater. Interfaces 11 (2019) 17863]. In this case, quite pure form factor scattering is observed. This somewhat “ideal” structure is further investigated here making use of reverse Monte Carlo simulations in order to shed light on the corresponding nanoparticle structure in space. By fixing the target “experimental” apparent structure factor to one over a given q-range in these simulations, we show that it is possible to find dispersions with this property. The influence of nanoparticle volume fraction and polydispersity has been investigated, and it was found that for high concentrations only a high polydispersity allows reaching a state of S = 1. The underlying structure in real space is discussed in terms of the pair-correlation function, which evidences the importance of attractive interactions between polydisperse nanoparticles. The calculation of partial structure factors shows that there is no specific ordering of large or small particles, but that the presence of attractive interactions together with polydispersity allows reaching an almost “structureless” state.

Ref HAL: hal-04244898_v1
DOI: 10.3389/frsfm.2023.1260211
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In the context of a more sustainable economy, bio-surfactants become increasingly important, due to their independence of petrol-based chemistry, their usually mild synthesis conditions, and in certain cases their pharmacological activity. We have recently discussed self-assembly studies in binary systems of bio-surfactants of microbial origin, or saponins extracted from plants (Hellweg et al., Frontiers in Soft Matter, 2023, 2). In the present review, we focus on the formation of microemulsions based on these molecules. We review the formation and structure of microemulsion systems formed by oil, water, and biosurfactants, with a particular focus on Quillaja saponins and rhamnolipids.

Ref HAL: hal-04235866_v1
DOI: 10.3390/cryst13060957
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In this paper, we numerically and experimentally show that the director field orientation degeneracy within the Translationally Invariant Configuration (TIC) of a cholesteric liquid crystal under an electric field can be lifted by imposing a magnetic field B parallel to the electrodes. The configuration can be either parallel or perpendicular to the magnetic field depending on the values of the sample thickness, pitch, and applied voltage, with two equiprobable orientations in each case. The transition between the parallel and perpendicular orientations has hysteresis, suggesting that it is first order. When B is slightly tilted with respect to the electrode plane, the indeterminacy on the TIC orientation is removed when the TIC is directed along B.

Ref HAL: hal-04232515_v3
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