Particle tracking Microrheology (PTM) is an attractive experimental technique to measure the viscoelastic properties of complex fluids in a tiny volume. In the case of anisotropic materials such as liquid crystals, it should be however used cautiously. Here, we examined the case of the lyotropic chromonic liquid crystal disodium chromoglycate (DSCG). The unusual Brownian motions of microspheres in this system has attracted recent attention [1,2] suggesting a complex coupling between the fluctuations of the director and of the beads. Although it has been claimed that PTM could be used to extract the viscosities of the nematic phase [3], this effect may give rise to inconsistent microrheological measurements.In order to explore these issues, we have experimentally studied the Brownian motion of particles in aligned samples (see figure 1.A), varying both the concentration of DSCG and the size of the probes. Effective viscoelastic properties have been extracted from these measurements and compared to the ones obtained by active microrheology based on optical tweezers. Our results explain why various viscoelastic behaviors have been previously reported for DSCG.

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.

Single-chain nanoparticles (SCNPs) are soft disordered nano-objects synthesized by intra-molecular bonding of linear polymer chains with a finite fraction of reactive groups allowing internal crosslinking of the molecule. They may be investigated as a mimick of, e.g., intrinsically disordered proteins, in particular with respect to the effect of the crowded cellular environment on macromolecular properties. Here the conformation of synthetic SCNPs in presence of linear polystyrene crowding molecules has been studied by small-angle neutron scattering under contrast-matching of the crowders[1]. A model describing the scattering of aggregating polydisperse SCNPs (see Figure 1) 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. Two different crowders – of low and high molecular weight, respectively – are shown to have a different effect: while long chains tend to impede their aggregation above their overlap concentration, short ones are found to mediate depletion interactions leading to aggregation. Self-imposed crowding within the aggregates has a similar impact on chain conformation independently of the crowding of the surrounding medium. Our results are compared to recent simulations and is hoped to contribute to the microscopic understanding of the phase behavior of soft intrinsically disordered nano-objects, and in particular the effect of crowding on biomacromolecules. Figure 1: Schematic representation of the aggregation process of two SCNPs of monomer numbers i1 and i2 described by the addition of their individual SCNP masses, and obeying the same local chain statistics.References[1] Julian Oberdisse, Marina González-Burgos, Ander Mendia, Arantxa Arbe, Angel J. Moreno, José A. Pomposo, Aurel Radulescu and Juan Colmenero, under (favorable) revision in Macromolecules.

This paper presents an efficient way to measure the curing kinetics and gel point, αgel, in epoxy resins from one single experiment. The epoxy curing reaction is herein monitored using in situ and time-resolved near-infrared absorption spectroscopy (NIR). The curing profiles over different isothermal conditions are in good agreement with DSC. Furthermore, the increase of the NIR absorption bands of aromatic rings (unreactive throughout curing) probe the cure shrinkage, as more and more aromatic rings are localized within the fixed sample volume. Therefore, the gel point is determined using the onset of the aromatic absorption increase. The results are in good agreement with the theoretical gel point, as well as DMA results. This innovative approach enables gelation measurements on epoxy neat resins and film composites with an easy-to-perform, accurate, robust, and versatile method.

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.

Polymerized ionic liquids (PolyILs) are promising materials for applications in electrochemical devices spanning from fuel cells to capacitors and batteries. In principle, PolyILs have a competitive advantage over traditional electrolytes in being single ion conductors and thus enabling a transference number close to unity. Despite this perceived advantage, surprisingly low room temperature ionic conductivities measured in the lab raise an important fundamental question: how does the molecular structure mediate conductivity? In this work, wide-angle X-ray scattering (WAXS), vibrational sum frequency generation (vSFG), and density functional theory (DFT) calculations were used to study the bulk and interfacial structure of PolyILs, while broad band dielectric spectroscopy (BDS) was used to probe corresponding dynamics and conductive properties for a series of the PolyIL samples with tunable chemistries and structures. Our results reveal that the size of the mobile anions has a tremendous impact on chain packing in PolyILs that wasn’t addressed previously. Larger mobile ions tend to create a well-packed structure, while smaller ions frustrate chain packing. The magnitude of these changes and level of structural heterogeneity are shown to depend on the chemical functionality and flexibility of studied PolyILs. Furthermore, these experimental and computational results provide new insight into the correlation between conductivity and structure in PolyILs, suggesting that structural heterogeneity helps to reduce the activation energy for ionic conductivity in the glassy state.