L’existence d’une phase « Nematique twist Bend » (NTB) a été prédite par I.Dozov dès 2001 [1] mais n’a été observée expérimentalement qu’en 2010 [2]. Cette phase est assez originale car elle présente optiquement des défauts de type coniques focales sans réel ordre translationnel observable en diffusion des rayons X. Généralement cette phase est présente à des températures élevées (au-dessus de 100°C) dans les corps purs. L’ajout d’un nématogène [comme le 4-Cyano-4'-pentylbiphenyl (5CB)] à un composé NTB [tels que le 1,7-bis (4-cyanobiphényl-4-yl) heptane (CB7CB)] permet de diminuer fortement la plage d’existence de la phase NTB [3] tout en modifiant continûment les propriétés thermiques et diélectriques. Dans ce travail, nous avons exploré les modifications dues à l’ajout au CB7CB de smectogènes, et en particulier du 4′-octyl-4-biphénylcarbonitrile (8CB). Le diagramme de phase de ce dernier mélange binaire présente des caractéristiques surprenantes. Malgré leur ressemblance macroscopique, les phases SmA et NTB semblent ainsi incompatibles et restent séparées par une phase nématique s’étendant à très basse température (-20 ° C) pour une fraction CB7CB de ϕ_c≈20%. Nous avons par ailleurs caractérisé les propriétés optiques, thermiques, diélectriques et d’ancrage des phases N et NTB des mélanges. Les propriétés optiques sont très différentes de celles du CB7CB sur une large gamme de composition et de forts effets pré-transitionnels sont observables à l'approche de ϕ_c≈20%. Les propriétés d’ancrage (fig1) sont également significativement modifiées par l'ajout de 8CB au CB7CB ce qui facilite l'alignement homéotrope, très difficilement obtenu pour le CB7CB.

Les enjeux de santé publique et de développement durable conduisent à intensifier l’utilisation de protéines végétales notamment dans les secteurs de biens de consommation comme l’industrie pharmaceutique,l’agro-alimentaire et les cosmétiques. La levée récente de certains verrous technologique permet aujourd’hui la purification industrielle de protéines végétales issus de tourteaux provenant de la production d’huiles végétales. Ces protéines sont valorisables comme substituts aux graisses saturées dans la structuration d’huiles à destination de la consommation humaine. Le manque de texture d’huiles végétales insaturées peut être compensé par ces protéines jouant le rôle de stabilisants et de gélifiants dans les émulsions. Nous nous intéressons aux propriétés fonctionnelles des protéines de blé, de tournesol et de colza, en volume et aux interfaces. Nous avons montré que des gels de protéines de tournesol avec des élasticités modulables sont obtenus par dénaturation thermique. La dynamique de formation de films protéique aux interfaces fluides a été étudiée en combinant des mesures de tensiométrie, de viscoélasticité dilatationnelle et d’ellipsométrie. Les mesures sur plusieurs ordres de grandeurs en concentrations et en temps mettent en évidence différents régimes de structuration associés à différentes dynamiques d’adsorption pour les trois protéines de blé, de tournesol et de colza étudiées. Nous discutons également le rôle de la flexibilité des protéines dans ces différents régimes de structuration.

The increase of plastics and microplastics in the environment is a major environmental challenge. Still, little is known about the degradation kinetics of macroplastics into smaller particles, under the joint actions of micro-organisms and physico-chemical factors, like UV or mechanical constraints. In order to gain insight into (bio)-degradation in various media, we perform accelerated erosion experiments by using a well-known enzymatic system. We show that the microstructure of semi-crystalline polymers plays a crucial role in the pattern formation at their surface. For the first time, the release of fragments of micrometric size is evidenced, through a mechanism that does not involve fracture propagation. A geometric erosion model allows a quantitative understanding of erosion rates and surface patterns, and provides a critical heterogeneity size, parting two types of behavior: spherulites either released, or eroded in situ. This new geometric approach could constitute a useful tool to predict the erosion kinetics and micro-particle generation in various media.

We investigate by time-resolved synchrotron ultra-small X-ray scattering the dynamics of liquid–liquid phase-separation (LLPS) of gluten protein suspensions following a temperature quench. Samples at a fixed concentration (237 mg ml−1) but with different protein compositions are investigated. In our experimental conditions, we show that fluid viscoelastic samples depleted in polymeric glutenin phase-separate following a spinodal decomposition process. We quantitatively probe the late stage coarsening that results from a competition between thermodynamics that speeds up the coarsening rate as the quench depth increases and transport that slows down the rate. For even deeper quenches, the even higher viscoelasticity of the continuous phase leads to a “quasi” arrested phase separation. Anomalous phase-separation dynamics is by contrast measured for a gel sample rich in glutenin, due to elastic constraints. This work illustrates the role of viscoelasticity in the dynamics of LLPS in protein dispersions.

Natural protein sources often display a huge complexity, being composed of a blend of polypeptides of various molecular weight, pHi and charge density. Gluten, the proteins extracted from wheat flour is one of such. Gluten is widely used for its viscoelastic properties as an improver of cereal products (bread, pastry, etc.). It is composed of two classes of proteins, named gliadin and glutenin, similar in their amounts in glutamine (30%) and proline (10%). The more than 25 different polypeptides belonging to the gliadin class are hard to fractionate into individual components because of high redundancy in the primary sequences. Glutenin are in the form of polymers made from several distinct polypeptides concatenated through inter-chain disulfide bonds. Their molecular weights are evenly distributed from 100 kg/mol to 7,000 kg/mol.While it is well established that gliadin confers viscosity to gluten whereas glutenin polymers are at the origin of its elastic resistance, the interactions existing between both classes of gluten protein remain unknown. We previously showed by SLS and multi-angle DLS that gluten proteins suspended in ethanol/water (50/50, v/v), a theta solvent, includes large proteins assemblies (26,000 kg/mol, Rh 100nm) displaying an internal dynamic1. To get a better insight of the composition of those assemblies, we combined biochemical and physicochemical approaches. On the one hand, gluten proteins suspended in ethanol/water were fractionated by Asymmetrical- Flow-Field-Flow Fractionation (A4F) coupled to UV, SLS and QELS detectors. On the other hand, gluten proteins were partitioned by liquid-phase decomposition in respect with temperature. Protein composition of partitioned phases and eluting fractions recovered from A4F were characterized by size-exclusion chromatography. A specific interaction between omega-gliadin and glutenin polymers was evidenced.This result strengthens a very recent study that demonstrates a significant positive correlation between glutenin polymeric proteins, the ω‐gliadin fraction, and dough properties.

Despite the relevance to environmental, biological and industrial processes, the motion of a colloidal particle close to a fluid interface and the way it interacts with the water surface are still largely elusive and intriguing physical phenomena.We explored the system of individual colloidal particles close to an air-water interface by recording highly resolved 3D trajectories through a dual wave reflection interference setup (DW-RIM). Contrary to other established experimental techniques, DW-RIM allows accurate measurements of the absolute particle-interface distance and thus does not require any calibration or assumption to know the location of the interface. The particle-interface system shows two different potential energy landscapes resulting to two different equilibrium particle-interface distances. The larger one can be fairly explained by Van der Waals and electrostatic interactions combined with gravity. The shorter one highlights the existence of an unexpected additional attractive interaction. Surface heterogeneities as possible origin of such an interaction are considered and discussed.Concerning the friction the particle undergoes, the air-water interface peculiarly acts as a slip boundary for the particle motion parallel to the interface and as a no-slip boundary for the perpendicular motion. This experimental result is rationalized considering recent models based on surface incompressibility.

Heliconal nematic twist bend (NTB) phases are usually not well oriented in planar commercial cells, even in thin (~1 µm) ones where a micron-sized periodic texture is usually observed [1,2,3] (see Fig.1-a). The origin of the stripe patterns is attributed to the rapid shrinking of the pseudo-layers below the N-NTB phase transition temperature, which yields an undulation instability. The observed periodicity is found to be twice the cell gap [1].
We have explored the effect of the strength of the anchorings of the substrates on the resulting patterns. We used polymer aligning layers of tunable azimuthal and zenithal strengths to design liquid crystal cells with surface anchorings ranging from ultraweak to strong. We then have studied the patterns formed by the NTB phase of 1,7-bis-4-(4-cyanobiphenyl) heptane (CB7CB). We will show how the period of the stripes can be varied in a large range in cells of the same thickness but with different anchoring preparations. With adequate anchoring conditions (see Fig.1-b-c), an excellent and spontaneous planar alignment of the NTB phase of CB7CB can be obtained much below the phase transition temperature.
[1] Panov V.P. et al; Spontaneous Periodic Deformations in Nonchiral Planar-Aligned Bimesogenswith a Nematic-Nematic Transition and a Negative Elastic Constant; Phys. Rev. Lett. ; 105; 167801; 2010.
[2] Challa P. K. et al; Twist-bend nematic liquid crystals in high magnetic fields; Phys. Rev. E: Stat., Nonlinear, Soft Matter Phys.; 89; 060501; 2014.
[3] Vaupotič N. et al.; Polarization Gratings Spontaneously Formed from a Helical Twist‐Bend Nematic Phase; Chem. Phys. Chem.; 19; 2566; 2018.