Glassy materials yield under large external mechanical solicitations. Under oscillatory shear, yielding shows a well-known rheological fingerprint, common to samples with widely different microstructures. At the microscale, this corresponds to a transition between slow, solid-like dynamics and faster liquid-like dynamics, which can coexist at yielding in a finite range of strain amplitudes. Here, we capture this phenomenology in a lattice model with two main parameters: glassiness and disorder, describing the average coupling between adjacent lattice sites, and their variance, respectively. In absence of disorder, our model yields a law of correspondent states equivalent to trajectories on a cusp catastrophe manifold, a well-known class of problems including equilibrium liquid-vapour phase transitions. Introducing a finite disorder in our model entails a qualitative change, to a continuous and rounded transition, whose extent is controlled by the magnitude of the disorder. We show that a spatial correlation length ξ emerges spontaneously from the coupling between disorder and bifurcating dynamics. With vanishing disorder, ξ diverges and yielding becomes discontinuous, suggesting that the abruptness of yielding can be rationalized in terms of a lengthscale of dynamic heterogeneities

We present an innovative template-free water-based sol–gel method to produce uniform mesoporous silica beads of millimeter size, which have tunable size, stiffness and porosity, and could be used for adsorption applications. Our protocol exploits an in-situ enzymatic reaction to produce spherical beads of hydrogel from a charge-stabilized suspension of silica nanoparticles confined in a millimetric drop suspended in a non-miscible oil. Once the gelation step is complete, the spherical bead of gel is cleaned from oil and deposited onto a hydrophobic surface and let dry. Separating the gelation to the drying steps ensures a spatially uniform gel and allows us to perform a solvent exchange before drying. For all beads, we observe a crack-free drying process leading to the formation of stiff quasi-spherical beads with diameter in the range 1 to 5 mm and Young modulus in the range (0.1‑2)GPa and narrow pore size distribution, centered around 10 to 25nm depending on the experimental conditions. Finally, to demonstrate the potentiality of these materials, we graft on the bead surface aminosilane molecules, and quantify their CO2 adsorption efficiency. Overall, the production method we have developed is simple, readily adaptable, and offers promising materials for adsorption, storage, catalysis and chromatography.

Protein nanoparticles have been proven to be highly effective stabilizers of water-in-water emulsions obtained from a number of different types of aqueous two-phase systems (ATPS). The emulsion stabilizing efficiency of such particles is attributed to their affinity to the water/water interface of relevant ATPS, and emulsion formulations with long-term stability were reported in the recent years. In this study we investigated the macroscopic dynamics of the early-stage time evolution of dextran-in-polyethylene glycol emulsions obtained from a single ATPS and containing β-lactoglobulin microgel particles of various diameters (ca. 40-190 nm). The results revealed the existence of a threshold in microgel size above which the water-in-water emulsion is stabilized, and that the process of segregative phase separation is determined by the interplay of droplets coalescence and sedimentation. Efficient droplet coalescence inhibition was found for microgel particles larger than 60 nm. Based on previous literature results, we discuss our coalescence-driven phase separation data in the context of the formation of durable particle layers on the emulsion droplets and the resulting droplet-droplet interactions.

Marine fouling of shipping vessels induces ecological disasters with the transport of invasive species as well as economical costs for shipping due to frictional resistance on the surface vessels. To address this issue, fouling release coatings, without toxic biocide, gradually replaced bioactive antifouling coatings. However, the main candidates, the silicones, offer limited static fouling which can be improved by using amphiphilic additive. To render more attractive the incorporation of additive in the paint formulation, they can additionally be photosensitive allowing to repel the marine organisms under light and mitigate the fouling formation. This study presents silicone coatings using photosensitive azobenzene polyoxazoline (POx) additive able to reversibly switch from trans to cis configuration under UV/Visible (Vis) light. To avoid any additive-matrix incompatibility, that is a current issue specific to commercial hydrophilic additives, amphiphilic POx were designed. Di- and triblock POx containing hydrophobic poly(2-phenyl-2-oxazoline) blocks and hydrophilic poly(2-methyl-2-oxazoline) blocks were covalently incorporated in PDMS matrix by crosslinking via self-condensation. The impact of the macromolecular architecture of additive, UV irradiation and Vis light exposure on the surface and the mechanical properties of resulting coatings was investigated by contact angle, Atomic Force Microscopy (AFM) and nanoindentation. The reversibility of the photo-response was also evaluated. Finally, the macrofouling properties of the coated surface mediated by UV/Vis light were monitored during 120 days by real-time immersion of coatings in Atlantic Ocean and macroscopic fouling evaluation of the immersed surfaces.

Functionalized mesoporous silica particles offer excellent chemical and morphological properties, making them ideal adsorbents or drug carriers. However, their synthesis involves several energy- and resource-intensive steps, resulting in high economic and environmental costs. In this study, we report a strategy for the direct design of mesoporous silica with ordered mesopores densely functionalized by polyacid chains. The aqueous process relies on polyion complex micelles acting as pH-responsive multifunctional agents. They are first associated to direct the mesostructure of silica, and are then dissociated by a change in pH to reveal the material's mesoporosity and yield functional pores. Ordered mesoporous particles with controlled structure and particle size were obtained, showing dense functionalization of up to 2.1 mmol.gSiO2−1 of carboxylic acid functions, which were fully accessible to ionic exchange in aqueous solution. These highly functionalized materials were then evaluated as reversible adsorbents for the removal of a cationic dye (auramine O). The results revealed high dye uptakes, from 130 to 237 mg.gSiO2−1, which were up to 193 % higher than those achieved with non-functional calcined mesoporous silica particles. These uptakes correlated with the mesoporous volume of the materials, with an average density of around one auramine molecule per nm3 of pore. In addition, the materials exhibited excellent dye adsorption/desorption cyclability by pH stimuli in aqueous solutions under mild conditions, with an average desorption efficiency of 96 % in just 30 min. These results therefore represent an attractive strategy for the design of efficient and sustainable adsorbents for water purification.

We investigate the spreading of falling ambient-temperature Newtonian drops after their normal impact on a quartz plate covered with a thin layer of liquid nitrogen. As a drop expands, liquid nitrogen evaporates, generating a vapour film that maintains the drop in levitation. Consequently, the latter spreads in inverse Leidenfrost conditions. Three drop-spreading regimes are observed: (i) inertio-capillary, (ii) inertio-viscous, and (iii) inertio-viscous-capillary. In the first regime, although the drop expansion is essentially driven by a competition between inertial and capillary stresses, it is also affected by viscous effects emerging from the vapour film, which ultimately favours the development of a shear flow within the drop. Interestingly, vapour film effects become marginal in both the second and third regimes, allowing the drop to undergo biaxial extension primarily. More specifically, in the inertio-viscous scenario, the expansion is driven by the balance between inertial and biaxial extensional viscous stresses in the drop. Finally, inertia, capillarity and drop viscosity are all relevant in the third regime. These physical mechanisms are underlined through a mixed approach combining experiments with multiphase three-dimensional numerical simulations in light of spreading dynamics analyses, energy transfer and scaling laws. Our results are rationalized in a two-dimensional diagram linking the drops’ maximum expansion and spreading time with the observed spreading regimes through a single dimensionless parameter given by the square root of the capillary number (the ratio of the viscous stress to the capillary stress).