Wed August 3rd 2011
16:00
HR Z109
Seminar Drop impact of non-Newtonian liquids on superhydrophobic surfaces at high Weber number
Marine Guémas

Details:

Drop impacts on solid surfaces has been studied in many ways these past few years. Focusing on drop spreading behavior, previous studies showed that drop deformation depend strongly on surfaces properties as well as on the balance between liquid inertia and capillary forces. When the impact occurs on superhydrophobic micropatterned substrates directional splashing can be observed with newtonian fluids like water or ethanol (Tsai et al., Soft Matter, 2011). Nevertheless drop impact process is not well define yet for non-newtonian fluids. Luu & Forterre (JFM, 2009) succeed to characterize the spreading with viscoelastic liquids as Carbopol in hydrophilic substrates, but failed to explain how the spreading on superhydrophobic materials (Magic Sand) occurs, which was highly underestimated by their scaling laws.
Our main goal is to reproduce Luu & Forterre's results by using both micropatterned superhydrophobic substrates and hydrophilic glasses for two non-newtonian fluids as Cornstarch (shear-thickening) and Carbopol solutions (shear-thinning & viscoelastic). In order to investigate this, we will study the maximal droplet spreading for Weber numbers up to 3000. We will show how the micropatterned structure critically alters the splashing threshold, which becomes directional for many different patterns. To our surprise, the superspreading regime observed by Luu & Forterre can not be reproduced on micropatterned structures, which suggest that surface properties and mechanics might be able to enhance the spreading of the droplet. This would suggest that impact on loose hydrophobic grained surfaces would present even less friction than structured superhydrophobic surfaces. On the other hand we found that Cornstarch, a highly non-newtonian liquid, spreads following the same scaling laws as those found for newtonian liquids, regardless the high-strain rates achieved in the high Weber number regimes experienced.
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The 10th Complex Motion in Fluids 2021
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