Evaporation dynamics of small sessile water droplets under microgravity conditions is investigated numerically. The water-air interface is free, and the surrounding air is assumed to be quasisteady. The droplet is described by Navier-Stokes and heat equations and its surrounding water/air gaseous phase with Laplace equation. In the thermodynamic conditions of the simulations presented herein, the evaporative mass flow is nonlinear. It shows a minimum that indicates the existence of qualitative changes in the evaporative regimes although the droplet is sessile. Due to temperature gradients on the free interface, Marangoni motion occurs and generates inside the droplet convection cells that furthermore exhibit small fluctuating motion as evaporation goes on.

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Steady state foams made of a pH sensitive surfactant, nonaoxyethylene oleylether carboxylic acid, with ion complexing properties was studied using small angle neutron scattering (SANS). The effect of pH variation and salt addition on the foam film thickness was investigated and discussed in terms of the influent parameters stabilizing the foam such as surface properties and electrostatic effects determined by tensiometry and zeta potential measurements. The decrease in the film thickness by adding mono (Na(+)) and divalent (Ca(2+)) salts is classically explained by screening of the double layer in foam films (transverse interactions). On the contrary, addition of acid or complexing ion (Nd(3+)) results in an increase in the film thickness and can be analyzed in terms of cohesive forces between surfactants at the liquid/gas interface (lateral interactions). pH and specific salt effects revealed that foams produced by nonaoxyethylene oleylether carboxylic acid are of interest in the potential use of this surfactant in ion separation process.

This article describes a new strategy to modify the drainage behaviour of aqueous foams with solid nanoparticles. While for high particulate concentrations the liquid flow can be slowed down owing to viscosity effects, we show that much less concentrated systems, but possessing peculiar physicochemical properties, can also strongly modify the drainage behaviour. Taking advantage of the agglomerated state of pyrogenic silica in aqueous media, highly porous macro-particles are specifically prepared in the initial foaming solutions. It is shown that their typical size and their intrinsic yield-stress properties enable them to be captured by the bubbles during the foam generation stage and subsequently to be retained in the foam channels, according to a geometrical criterion based on the particle/bubble sizes ratio. The drainage curves of the foams display significant retention rates for the suspension during several hours, an effect that is enhanced for higher particles concentrations. This has been related to the high internal porosity and hydrophilic character of the macroparticles, acting as liquid-traps in the foam microstructure.

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International audienceFollowing the approach initially proposed in Maury & Venel [30, 31], we consider here crowd motion from the standpoint of granular media, and we investigate how theoretical and numerical tools in non-smooth analysis can help better understanding some paradoxical features. We shall be especially interested in evacuation processes, jams, and we will detail how the granular nature of the flow helps to understand two well-known phenomena, the so-called " Faster is Slower " effect, and " Stop-and-Go " waves

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International audienceThis paper investigates the effects of different surface treatments on the mechanical resistance of interface between wires of NiTi shape memory alloy and silicone rubber. Three different treatments were used; primer, plasma and combination of both. The wires deoxidation effects have also been studied. In order to characterize the interface properties in such composite material, pull-out tests were carried out by means of a home-made device. This test allows us to evaluate the mechanical resistance of the interface in terms of the maximum force reached during the test. First, results show that the debonding force is not higher after the wires deoxidation. This preparation is therefore not necessary. Second, using a primer PM820 and plasma separately leads to a significant improvment of the mechanical resistance. Third, the combination of these treatments (primer followed by plasma) and a longer time of exposure to the plasma alone get the debonding force higher. Consequently, NiTi/silicone rubber interface improved only by means of plasma offers a new way to obtain biocompatible interfaces in such composite material