Different adsorption behaviors of methane and carbon dioxide in the isotypic nanoporous metal terephthalates MIL-53 and MIL-47

A distinct step in the isotherm occurs during the adsorption of CO2 on MIL-53 at 304 K. Such behavior is neither observed during the adsorption of CH4 on MIL-53 nor during the adsorption on the isostructural MIL-47. This phenomenon seems to be due to a different mechanism than that of previous adsorption steps on MOF samples. It is suggested that a breathing behavior is induced in MIL-53 during CO2 adsorption.     

Characterization of the disordered phosphate network in CaO-P2O5 glasses by P solid-state NMR and Raman spectroscopies

In this study, the disordered network of calcium phosphate glasses is investigated by Raman scattering and ³¹P magic angle spinning (MAS) solid-state NMR spectroscopies. The use of both spectroscopies in a combined approach allows drawing a detailed understanding of the structure of these glasses. The P―O―P connectivity between successive PO₄ tetrahedra is probed using through-bond double quantum-single quantum (DQ-SQ) and triple quantum-single quantum (TQ-SQ) MAS NMR correlation experiments. Over the broad range of glass compositions studied here, two very different phosphate network topologies are encountered. The results obtained for the polyphosphate compositional range (above 50 mol% Ca) allow determining the phosphate chain-length distribution in the glass as a function of the modifier cation content. For the ultraphosphate region (below 50 mol% Ca), the network topology undergoes a sudden change close to 39 mol% Ca which can be interpreted in terms of a rigidity transition.     

Softening induced instability of a stretched cohesive granular layer

We report on a cellular pattern which spontaneously forms at the surface of a thin layer of a cohesive granular material submitted to in-plane stretching. We present a simple model in which the mechanism responsible of the instability is the "strain softening" exhibited by humid granular materials above a typical strain. Our analysis indicates that such a type of instability should be observed in any system presenting a negative stress sensitivity to strain perturbations.     

Equilibrium Problems for Vector Potentials with Semidefinite Interaction Matrices and Constrained Masses

We prove existence and uniqueness of a solution to the problem of minimizing the logarithmic energy of vector potentials associated to a d-tuple of positive measures supported on closed subsets of the complex plane. The assumptions we make on the interaction matrix are weaker than the usual ones, and we also let the masses of the measures vary in a compact subset of $\mathbb{R}_{+}^{d}$ . The solution is characterized in terms of variational inequalities. Finally, we review a few examples taken from the recent literature that are related to our results.     

Dynamic Wetting Properties of Mesh Substrates with Tunable Water Adhesion

In nature, wetting phenomena are present nearly everywhere and are a source of inspiration for liquid transportation. A good understanding of the underlying dynamic phenomena that governs wettability is therefore extremely important for researchers involved in bio-inspired surfaces. Herein, we study the adhesive behavior with water of mesh substrates modified with structured copolymers in order to tune the surfaces from parahydrophobic states (high water adhesion) to superhydrophobic states (low water adhesion). Using the ejection test method (ETM), a new technique that consists of the ejection of water droplets deposited onto a substrate with the aid of a catapult system, we experimentally demonstrate that the elasticity of the mesh substrate can be exploited for efficient vertical actuation of droplets.