Temperature induced non-contact bouncing failure

Water droplets usually bounce on superhydrophobic surfaces due to the air layer stabilized between the liquid and the solid by the surface texture [1]. In the absence of surface texture, bouncing still occurs for moderate Weber numbers if the surface is sufficiently flat [2-4]. Rebound is mediated by a thin air film acting as a cushion for the droplet, reducing and then reversing its momentum.

Here we study the case of hot water droplets impacting on a liquid-infused surface kept at room temperature. We show that the critical impact velocity at which droplet bouncing stops decreases significantly when the temperature difference increases. Using Reflection Interference Contrast Microscopy, we show that water condensation forms on the lubricant layer, creating a liquid roughness that triggers the contact between the drop and the substrate. We develop a theoretical model to account for condensation in the air layer and predict the outcome of the impact.

References

[1] Hartley, G. S. and Brunskill, R. T. Surface Phenomena in Chemistry and Biology (ed. by J. F. Danielli, K. G. A. Pankhurst & A. C. Riddiford), Pergamon Press, London, pp. 214-223, 1958.

[2] Kolinski, J. M. et al., Europhysics Letters, 108, 24001, 2014.

[3] De Ruiter, J. et al., Nature Physics, 11, 48-53, 2015.

[4] Hao, C. et al., Nat Commun, 6, 7986, 2015.