Laboratoire Matière et Systèmes Complexes

DRYING IN ARTIFICIAL LEAVES AND CAPILLARY DAMPING OF LIQUID OSCILLATIONS

Benjamin DOLLET

Laboratoire Interdisciplinaire de Physique, CNRS/Université Grenoble Alpes.

In this seminar, I will present two topics : drying in artificial leaves, and capillary damping of liquid oscillations.

First, tree and plant mortality under drought is mostly due to the nucleation of embolisms in leaves by cavitation, and to their subsequent growth, which eventually blocks sap circulation. Embolism growth occur by pervaporation of water from the sap veins to the dry outer air through the body of the leaf. To better understand this process, we propose a model experiment : pervaporation of water from channels embedded in PDMS, which is a water-permeable medium. We show that drying dynamics follows a truncated exponential law, and study the influence of the geometrical parameters (channel cross-section, PDMS thickness). We rationalise these results by an analytical and fully predictive model which solves the diffusion of water in PDMS and in the air-filled part of the channels. Preliminary results on drying by pervaporation in channel networks will be presented.

Second, sloshing describes the oscillations of liquids in reservoirs. It is often detrimental : coffee spilling, safety of tankers and spacecrafts, hence understanding and optimising its damping is of primary importance for applications. The role of triple line dynamics on damping has long been recognised, but has heretofore remained poorly understood. We study its role in the simplest sloshing configuration : the oscillation of a column of liquid in a U-shaped tube. We show that contact line pinning leads to strong effects : a less viscous liquid can display more damping than a more viscous one, liquid oscillations can arrest in finite time like in solid friction, and strong nonlinear responses, like a marked dependence on the initial amplitude, occur. We rationalise quantitatively all these observations by a hydrodynamic model accounting for contact angle hysteresis.