Nonlinear dynamics of confined soft objects : from oil in porous media to tree embolism

In a first part, I will present a study realized at PMMH (Paris) related to the transport of viscous oil drops in microchannels. Understanding the viscous dissipation mechanism in the transport of drops in confined media is of primary importance for industrial processes such as enhanced oil recovery or underground C02 storage. When a non-wetting and highly viscous oil droplet moves in a confined microchannel, viscous dissipation is mainly localized in a thin lubricating film which isolates the drop from the walls and amplifies its mobility [1]. I will show how the introduction of roughness on the surface of the walls can dramatically alter the dynamics due to the relocalization of viscous dissipation in the bulk of the viscous drop, which substantially decreases its mobility by orders of magnitude. The transition between those two dissipation modes is brutal, and drops can jump from one state to the other by slightly modifying the parameters of the experiment [2]. I will then discuss how this roughness-induced dissipation transition can open perspectives for the manipulation of a wider class of soft objects such as capsules, vesicles or living cells.

In a second part, I will present a study realized at LIPhy (Grenoble), and pursued at INPHYNI (Nice) related to air embolism formation in plants and trees. Global warming will lead to increasingly severe droughts and threatens most of the forests across the globe [3]. One of the main dangers of droughts for trees comes from the generation of air embolism, which impairs the sap conduction and potentially leads to their death. In leaves, embolism formation was shown to occur with intermittency and to exhibit catastrophic events [4]. By using PDMS-based biomimetic leaves to reproduce evapo-transpiration (see illustration), we will show that the presence of narrow constrictions in the leaf veins enables to recover intermittent embolism propagation. This intermittency will be shown to originate from an elastocapillary coupling between the air-water interfaces and the compliant structure of the biomimetic leaf venation [5].  I will then present various perspectives opened by the validation of our leaf-on-a-chip.

References :

[1] Keiser, L., Jaafar, K., Bico, J., & Reyssat, E. (2018). Dynamics of non-wetting drops confined in a Hele-Shaw cell. Journal of Fluid Mechanics, 845, 245-262.

[2] Keiser, L., Keiser, A., L’estimé, M., Bico, J., & Reyssat, É. (2019). Motion of viscous droplets in rough confinement: paradoxical lubrication. Physical review letters, 122(7), 074501.

[3] Brodribb, T. J., Powers, J., Cochard, H., & Choat, B. (2020). Hanging by a thread? Forests and drought. Science, 368(6488), 261-266.

[4] Brodribb, T. J., Bienaimé, D., & Marmottant, P. (2016). Revealing catastrophic failure of leaf networks under stress. Proceedings of the National Academy of Sciences, 113(17), 4865-4869.

[5] Keiser, L., Marmottant, P., & Dollet, B. (2022). Intermittent air invasion in pervaporating compliant microchannels. Journal of Fluid Mechanics, 948, A52