Dynamics of viscoelastic drops impacting onto a hydrophobic solid substrate

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In this paper, the impact of a viscoelastic drop onto a hydrophobic solid substrate is numerically investigated at low Weber number and Reynolds number. Previous experiments showed that viscoelastic fluids could make a big difference to drop spreading and retraction after impact, compared to Newtonian fluids. To quantitatively study the effect of viscoelasticity, Oldroyd-B model and diffuse interface methods are adopted in the direct numerical simulation of viscoelastic drops impacting onto a hydrophobic solid surface. The viscoelasticity is represented by the Deborah number, which is the ratio of the relaxation time of the viscoelastic fluid to the flow characteristic time. Based on the numerical results, we find that the spreading process is hardly affected by the viscoelasticity, and follows the scaling law: tm∼WeRm3/2 , where Rm is the maximum radius of the wetted area and tm is the corresponding time. During the drop retraction, the Newtonian drop would bounce up from the substrate. By contrast, the retraction velocity of the viscoelastic drops gradually slow down with the increase of Deborah number, thereby eventually suppressing the drop bouncing. The mechanism of anti-rebound effect due to the viscoelasticity can be interpreted by the occurrence of the downward elastic stress near the interface, and the bigger the Deborah number is, the more likely the bouncing is inhibited.

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