Séminaire de Céline Cohen

02/10/2020

Wetting dynamics of complex superhydrophobic surfaces

Superhydrophobic surfaces feature remarkable water repellency which are widely known to be governed by a combination of roughness at the micro/nano scale and low surface energy. Because of their considerable practical importance, they have been the center of extensive research for the last decades, both in terms of manufacturing and microfabrication and in terms of fundamental studies of these “super-surfaces” which exhibit noteworthy behaviors such as rebound, drag reduction, anti-icing...

In this seminar, I will present two different microfabrication methods for generating complex surfaces (curved, microtextured, transparent, hybrid hydrophilic-superhydrophobic). Two different studies of wetting properties will be exposed:

- the exploration of contact line dynamics on curved superhydrophobic surfaces (Fig.1b) using an unconventional method of the capillary bridge [1,2].

- the study of hysteresis on hybrid surfaces (Fig 1d.) [3].

In the first study, we show that for superhydrophobic microtextured surfaces, both receding and advancing contact angle increase with decreasing micropillar density. In addition, receding contact angle measurements are in very good agreement with the contact line elasticity theory recently proposed by Dubov et al. [4] but that for advancing contact angle the model should be refined. Moreover, we show how the capillary bridge experiment allow to measure the relation between the contact angle and the contact line speed (Fig 1.c). This important result confirms the fact that the capillary bridge setup is a efficient tool to explore problematic of liquid friction in a liquid corner. In the second study, we develop hybrid microtextured surfaces, constituted of hydrophilic micropillars on a surface that could be covered with superhydrophobic polymers. We show that both advancing and receding contact angles increase strongly when the quantity of deposited polymer (electrodeposition charge) increases above a critical charge value (that is higher for receding angles). We also measure that advancing and receding contact angle respectively increase and decrease with increasing pillar density which differs from behaviour usually observed for classic superhydrophobic surfaces. We interpret qualitatively these behaviors, the main point being how important is the impalement (null, partial or total).

Seminaire_CCohen

[1] Restagno F., Poulard C., Cohen C., Vagharchakian L., Léger L., Langmuir, 25, (2009).

[2] Cohen C., Bouret Y., Izmaylov Y., Sauder G., Forestier E. and Noblin X., Soft Matter, 15, 2990-2998 (2019).

[3] Cohen, C., Darmanin, T., Priam, J., Guittard, F., & Noblin, X., Soft Matter, 15, 9352-9358 (2019).

[4] Dubov A. L., Teisseire J. and Barthel E., EPL, 97, (2012).

Partager cet article :