Cyril Picard

Giant Osmotic Pressure in the Forced Wetting of Hydrophobic Nanopores.

The forced intrusion of water in hydrophobic nanoporous pulverulent material is of interest for quick storage of energy. With nanometric pores the energy storage capacity is controlled by interfacial phenomena. With subnanometric pores, we demonstrate that a breakdown occurs with the emergence of molecular exclusion as a leading contribution. This bulk exclusion effect leads to an osmotic contribution to the pressure that can reach levels never previously sustained. We illustrate, on various electrolytes and different microporous materials, that a simple osmotic pressure law accounts quantitatively for the enhancement of the intrusion and extrusion pressures governing the forced wetting and spontaneous drying of the nanopores. Using electrolyte solutions, energy storage and power capacities can be widely enhanced.

A micro-nano-rheometer for the mechanics of soft matter at interfaces

We present a nano-rheometer based on the dynamic drainage flow between a sphere and a plane from bulk regime to highly confined regime. The instrument gives absolute measurements of the viscosity of simple liquids in both regimes. For complex fluids, the measurements involve the viscosity and the elastic modulus. The device operates on distances ranging over four orders of magnitude from 1 nm to 10 μm, bridging rheological properties from the macroscopic to the molecular scale. This allows to measure an hydrodynamic or visco-elastic boundary condition and to explore the causes of the boundary condition at the microscopic level.

Transient aging of a liquid–gas interface stretched by standing waves: On the interplay of chemical kinetics

This article discusses the aging of a liquid surface enriched with surface active species and suddenly perturbed by standing capillary waves. Special attention is paid to deriving an accurate initial condition of the surface elevation. Due to the arising of the waves, the sub-phase and surface concentrations, C and Gamma, which were initially uniform and controlled by thermodynamic equilibrium, are modified by a transient oscillatory regime. A complete analytical description of the time-dependent carrier wave and oscillating chemical modulations associated with these concentrations is proposed for: (1) a small surface elevation, (2) a weak coupling with momentum transport, (3) but a strong coupling between all chemical transport phenomena which might be involved during transient regime: surface adsorption/desorption, 3-D diffusion within the sub-phase as well as near the liquid surface, and 2-D chemical diffusion along the surface. Analytical expressions resulting from regular perturbation series are compared to the limit aging regimes most commonly invoked in the literature, namely, diffusion- or sorption-limited surface aging. Finally, the (surface) compositional elasticity due to the arising of surface tension gradients is derived.

A Direct Sensor to Measure Minute Liquid Flow Rates

Nanofluidics finds its root in the study of fluids and flows at the nanoscale. Flow rate is a quantity that is both central when dealing with flows and notoriously difficult to measure experimentally at the scale of an individual nanopore or nanochannel. We show in this letter that minute flow rate can be directly measured accumulating liquid over time within the compliant membrane of a commercial piezoresistive pressure sensor. Our flow rate sensor is versatile and can be operated independently of the nature of the liquid, flow profile, and type of nanochannel. We demonstrate this method by measuring the pressure-driven flow of silicon oil in a single nanochannel of average radius 200 nm. This approach gives reliable measurement of the flow rate up to 1 pL/min. Unlike other nanoscale flow measurements methods based, for instance, on particle tracking, our sensor delivers a direct voltage output suitable for nanoflow control applications.