Network-forming materials are ubiquitous and appear in industrial products such as tires, food andcosmetics as well as composing the cytoskeleton within the cells of living organisms. They arelightweight and display properties such as optical transparency and reversible deformability up to largestrains. However, microscopic mechanisms protecting a network against macroscopic fracture and theprocesses that control crack growth are still poorly understood. A deeper understanding is needed tofully exploit the potential of polymer networks in advanced and novel material design. To this end, weadapt photon correlation imaging [1] (PCI) to reveal the microscopic rearrangements within poly(ethylacrylate) networks [2] during deformation by extension and fracture (see figure 1).PCI creates a time-resolved macroscopic map (field of view of several mm) of the microscopicmovements (on the order of 1µm) induced by the applied strain preceding fracture. We find that, in ournearly transparent samples, surface scattering dominates the PCI signal, obscuring bulk rearrangements.To address this issue, we first minimise surface scattering by immersing the sample in a pool filled withrefractive index matching glycerol, where the geometry of the pool walls is carefully designed to avoidreflections. Furthermore, the pool design allows PCI to be performed at both high (176o) and low (4o)angles simultaneously to measure rearrangements of the polymer network on length scales of 200 nmand 5 µm, respectively. Second, we introduce melamine formaldehyde nanoparticles to the polymernetworks to increase the scattering from the bulk. Preliminary measurements reveal non-affinecontributions even at low strain, well within the linear regime. We will continue by investigating therole that network architecture, such as interpenetrated multiple networks [3,4], has in the dynamicresponse of the network and the resultant resistance to fracture. References[1] A. Duri, D. A. Sessoms, V. Trappe, and L. Cipelletti Phys. Rev. Lett., 2009 102(8), 085702.[2] P. Millereau, E. Ducrot, J. M. Clough, M. E. Wiseman, H. R. Brown, R. P. Sijbesma, and C.Creton, PNAS, 2018 115(37), 9110–9115.[3] J. P. Gong, Y. Katsuyama, T. Kurokawa, and Y. Osada Adv. Mater., 2003 15, 1155.[4] E. Ducrot, Y. Chen, M. Bulters, R. P. Sijbesma, and C. Creton Science, 2014 344, 186.

Liquid/liquid (L/L) interfaces play a key, yet poorly understood, role in a range of complex chemical phenomena where time-evolving interfacial structures and transient supramolecular assemblies act as gatekeepers to function. Here, we employ surface-specific vibrational sum frequency generation combined with neutron and X-ray scattering methods to track the transport of dioctyl phosphoric acid (DOP) and di-(2-ethylhexyl) phosphoric acid (DEHPA) ligands used in solvent extraction at buried oil/aqueous interfaces away from equilibrium. Our results show evidence for a dynamic interfacial restructuring at low ligand concentrations in contrast to expectation. These time-varying interfaces arise from the transport of sparingly soluble interfacial ligands into the neighboring aqueous phase. These results support a proposed "antagonistic" role of ligand complexation in the aqueous phase that could serve as a holdback mechanism in kinetic liquid extractions. These findings provide new insights into interfacially controlled chemical transport at L/L interfaces and how these interfaces vary chemically, structurally, and temporally in a concentration-dependent manner and present potential avenues to design selective kinetic separations.

This research was carried out to examine the distribution of enzymatic activities of some tissues (liver, muscles and gills) of selected aquatic organisms (Nile tilapia, Mullet fish and Crab) collected from some crude oil polluted rivers (Abuloma Jetty and Woji Jetty) and Ojimba-ama a non-oil polluted area which served as control. The aquatic organisms were obtained from rivers which are used as jetty for transportation of petroleum products and other industrial activities like welding, dredging, refuse dump, etc. Enzyme activities of fish and crab tissues (liver, muscles and gills) were measured for some biomarker enzymes such as catalase, rhodanase and glutathione S-transferase. Results were shown in means of triplicate values which were subjected to statistical analysis using analysis of variance (ANOVA). Enzyme activity in Nile tilapia across the three locations ranged from 44.39±0.01 μ/mgprotein to 171.45±0.01 μ/mgprotein with GST in gills having the lowest value and rhodanase in the liver recording the highest value. Enzyme activity in Mullet across the three locations ranged from 18.58±0.10 μ/mgprotein to 120.37±0.02 μ/mgprotein with catalase in muscles having the lowest value and rhodanase in the liver recording the highest value. Enzyme activity in Crab across the three locations ranged from 40.79±0.03 μ/mgprotein to 130.72±0.01 μ/mgprotein with GST in gills having the lowest value and rhodanase in the liver recording the highest value. Rhodanase showed the highest level of enzyme activity in all the tissues. Liver recorded the highest enzyme activity across all samples from the three locations which may be as a result of the liver being the principal detoxification organ for xenobiotic substances. From this study, there was an increase in the enzyme activities of the biomarkers across all the tissues which indicate a contamination from pollutants capable of causing oxidative stress in the organisms.

L’optimisation des pulvérisations phytosanitaires sur les grandes cultures est un enjeu environnemental et sanitaire majeur. C’est dans ce contexte, qu’en partenariat avec la Compagnie Fruitière, leader européen dans la production de bananes, nous étudions les mécanismes d’interactions physico-chimiques de formulations phytosanitaires modèles avec les feuilles de bananier. Ces formulations sont développées pour lutter contre la Cercosporiose noire du bananier, une des maladies les plus graves pour la production des bananes qui cause des pertes importantes de rendement et de qualité des fruits. Nous comparons après mise en contact avec une feuille de bananier, les propriétés d’impact, d’étalement et d’imprégnation d’une huile minérale seule, d’émulsions directes de cette huile utilisées actuellement par notre partenaire, et d’émulsions inverses originales de cette même huile.Dans un premier temps, nous caractérisons la stabilité la distribution de taille des gouttelettes de la phase dispersée ainsi que les propriétés rhéologiques des différentes émulsions.L’impact de gouttes individuelles des différentes formulations sur une feuille de banane est visualisé par une caméra rapide. L’analyse de la dynamique d’impact révèle qu’aux temps courts (<10ms), les gouttes d’émulsion directe exhibent un phénomène d’éclaboussures qui génère l’émission de gouttelettes secondaires issues de la goutte initiale après impact sur la feuille, puis se rétractent ; au contraire, les émulsions inverses s’étalent sans se déstabiliser et sans rétractation, de manière assez similaire aux gouttes d’huile pure. L’absence d’éclaboussures pourrait constituer un avantage des émulsions inverses par rapport aux émulsions directes, tant en termes de réduction de la dispersion de la maladie que du risque phytosanitaire de pollution des sols. L’évolution de l’étalement d’un volume contrôlé de sprays de ces différentes formulations sur la feuille de banane est quantifiée. On observe, dans tous les cas un étalement anisotrope, privilégié dans la direction des rainures secondaires de la feuille. Aux temps longs (t<35min)) toutes les formulations exhibent une évolution lente du taux de couverture du spray suivant une loi de puissance ta, α=0.27±0.05 compatible avec la loi de Tanner pour l’’étalement d’une goutte individuelle. Cependant l’étalement des sprays de gouttes d’émulsion directe est précédé par une période de latence (t<2min) où le taux de couverture n’évolue pas. L’imprégnation de l'huile et des émulsions est étudiée par micro-spectroscopie infrarouge. À la suite du dépôt d’un film épais d’huile sur la surface, les cartographies infrarouges démontrent que l'huile s'accumule principalement dans les parenchymes palissadiques des feuilles. Les études de dynamique d’imprégnation suggèrent une diffusion de Fick de l’huile précédée avec un coefficient de diffusion effectif D = (1.2±0.8) ×10−12 m2/s, précédé d’une d’un temps de latence de l’ordre de 3.6 heures. Dans les mêmes conditions expérimentales, pour les émulsions inverses, l'imprégnation de l'huile est observée, mais absente dans le cas d'une émulsion directe. Ce résultat suggère le rôle majeur de l’interface huile /feuille dans le processus d’imprégnation. L'imprégnation des émulsions sous forme d'un spray est elle aussi quantifiée et confirme un mécanisme d’imprégnation privilégié pour l’émulsion inverse.

Lecture given at the ILL Soft Matter Summer school 2023

In order to explore the structural mechanisms responsible for the plastic behaviour and polyamorphism in silica glass, we perform Molecular Dynamics (MD) simulations within the framework of Density Functionnal Tight-Binding (DFTB) approach [1]. The DFTB method provides a description of atomic interactions with an accuracy almost similar to standard ab initio methods used in materials science (e.g. Density Functional Theory), but with a computational loading considerably lower. Recently, the DFTB approach applied to compressed silica (SiO2) glasses has shown that the structural changes from low- to high-density amorphous structures occur through a sequence of percolation transitions [2]. These transitions also provide an explanation of some of the mechanical properties of silica glass such as the Bulk modulus. Thus, the presence of percolation networks in silica glass sheds light on amorphous-amorphous phase transitions. In the present work, we present a more in details analysis of the local structures, their connectivity and features at medium range order. Hence, we have studied how the conformation of various polyhedra does change under compression, as well as how the network connectivity evolves from corner-sharing to edge- and face-sharing. We have also investigated the rings distribution and their conformation under pressure. We also present some results obtained for decompressions starting at pressures above the elastic to plastic limit around 10 GPa. In particular, we have observed various hysteresis for the pressure dependence of the density, the structural properties and percolation transitions. [1] M. Elstner and G. Seifert. Density functional tight binding. Phil. Trans. R. Soc. A, 372, 2014.[2] A. Hasmy, S. Ispas, and B. Hehlen. Percolation transitions in compressed SiO2 glasses. Nature, 599,2021.

Lecture on contrast given at a GDR Slamm workshop