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Tribologie Physico-chimie et dynamique des interfaces Dynamique des systèmes complexes Mécaniques matériaux et procédés Géomatériaux et constructions durables

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Actualités > 25/01/18 Café scientifique : Céline COHEN

25/01/18 Café scientifique : Céline COHEN

par Gallitre Laurence - 25 janvier

Le prochain café scientifique invité aura lieu jeudi 25 janvier 2018 de 13h à 14h en amphi 203 : Mouillage de surfaces texturées complexes, par Céline Cohen, maître de conférences à l’Institut de Physique de Nice (INPHYNI).
« Keywords » : Wetting, Hysteresis, Complex Surfaces, Capillary bridge, Impalement.

Abstract :
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. Despite this intense research activity, obtaining superhydrophobic surfaces, robust, versatile and easy to implement is still a current issue in particular in case of non-flat surfaces [1, 2].
We present here a novel fabrication method to obtain new complex superhydrophobic surfaces : transparent, curved and textured. This method consist in taking advantage of the deformable nature of crosslinked PDMS to reproduce regular patterns (micro-plots) obtained by photolithography, on the desired curved substrate using micro printing method. The aim of our study is then to study wetting properties (advancing and receding contact angles) of those complex surfaces with unconventional method : the capillary bridge technics [3]. Indeed, to our knowledge, apparent contact angles on superhydrophobic surfaces were measured so far using a goniometer in combination with a video camera and a drop shape analysis. Recent experiments of Schellenberger et al. [4] show that this method can significantly underestimate apparent advancing contact angle. We have used capillary bridge setup to explore textured superhydrophobic surfaces and show that both receding and advancing contact angle increase with decreasing of pillar density. In addition, comparing, those measures with ones realized with a classical sessile drop setup, we show that advancing apparent contact angles measured with capillary bridge technic are systematically higher than ones measure with sessile drop method which is in good agreement with Schellenberger et al. experiments. Moreover, wetting behavior of our surfaces observed with capillary bridge measurement could been explained with the model proposed by Extrand [5]. This model is based on contact line density approach and has been able to explain other experiments in the literature [6, 7] and in particular the recent publication by Schellenberger et al. [8]. Finally, capillary bridge experiments allow to explore wetting contact area much bigger than contact area generally explored with a simple millimetric droplet. This allows us to observe new impalement transition behaviors which can be brutal or progressive, and also reversible or irreversible as function of experimental conditions.

[1] Roach P., Shirtcliffe N. J., Newton M. I., Soft matter, 4(2), 224-240, 2008.
[2] Nosonovsky M., Bhushan B., Current Opinion in Colloid & Interface Science, 14(4), 270-280, 2009.
[3] Restagno F., Poulard C., Cohen C., Vagharchakian L., Léger L., Langmuir, 25(18), 11188-11196, 2009.
[4] Schellenberger F., Encinas N., Vollmer D., Butt H. J., Physical review letters, 116(9), 096101, 2016.
[5] Extrand C. W., Langmuir, 18(21), 7991-7999, 2002.
[6] Öner D., McCarthy T. J., Langmuir, 16(20), 7777-7782, 2000.
[6] Bico J, Marzolin C, Quéré D, Europhys Lett, 47(2), 220, 1999.
[8] Extrand, C. W., Journal of Adhesion Science and Technology, 30(15), 1597-1601, 2016.


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