Spreading behavior of an impacting drop on a structured rough surface

Abstract

The spreading of water drops impinging on structured rough surfaces is studied experimentally. The rough surfaces are specially prepared with a regular pattern of surface asperities. The arrangement of the square-shaped surface asperities creates channel-like grooves on the surface. A video microscope along with a controlled light exposure system is used to construct the image sequences of the spreading process. The images are digitally analyzed to measure the temporal variation of the spreading drop diameter 2R. Results are obtained for three rough surfaces with varying asperity heights in the range of 100-500 m and for different impact drop conditions with Weber number We in the range of 35-225. The results on the temporal variation of 2R show that, on the structured rough surfaces, the spreading occurs simultaneously both inside and above the texture pattern of the surfaces. For a given surface geometry, the volume of liquid flowing inside the grooves of the surface increases with increasing We. Consequently, the values of 2R measured inside the texture pattern are larger than those measured above the texture pattern, and their difference increases with increasing We. The arrangement of the surface asperities influences the spreading pattern of an impacting drop spreading axisymmetrically. For the texture geometry used in the present study, the spreading pattern resembles a regular rhombus shape for the impact of low We drops and becomes complex at high We. The spreading distances, measured both inside and above the texture pattern of the structured rough surfaces, are nearer to the measurements recorded on the smooth surface if the asperity height of the rough surface is smaller than the thickness of the spreading liquid lamella; however, the surface asperities influence the spreading pattern drastically and create a liquid splash.

Drop impact on microwetting patterned surfaces

“…Drop impact onto microfabricated rough surfaces was studied to show the effects of the surface texture patterns in guiding liquid flow and promoting splashes. [19][20][21] Unlike previous studies, which mainly relied on surface topography to control drop impact behavior and postdeposition shapes, here we show that the micropatterning of wettability of the target surface gives rise to the shape evolution of a drop and the final deposit shape that are novel and even aesthetically pleasing.…”

Granule formation mechanisms and morphology from single drop impact on powder beds

“…A better explanation of the nucleation mechanism requires the study of impacting drops. There is a large body of work that investigates drop impact on liquids, solids, and even porous solids [11][12][13][14][15]. Some of these concepts apply to drops impacting on powders, although the powder system is much more complex.…”

Effect of Substrate Concave Pattern on Splat Formation of Yttria-Stabilized Zirconia in Atmospheric Plasma Spraying

“…Dimples that located under the middle to peripheral region of the splat were not fully filled by the splat, which was similar to the case of alumina splats (Ref 3), suggesting that the droplet spread over the dimple-pattern substrate without filling these dimples at least in the later stage of spreading. This might be because the contact pressure of a spreading droplet is lower in the middle to peripheral regions than in the center region (Ref 5,24,25), resulting in the dimples being not filled. The dimples locating at the center region of the splat were filled by the splat.…”