Maximum Spreading of Liquid Drops Impacting on Groove-Textured Surfaces: Effect of Surface Texture

• Published in: Langmuir 2016-03, Vol.32 (10), p.2399-2409
• Main Authors: Vaikuntanathan, Visakh, Sivakumar, D
• Format: Article
• Language: English
• ISSN: 0743-7463; 1520-5827
• DOI: 10.1021/acs.langmuir.5b04639

Maximum spreading of liquid drops impacting on solid surfaces textured with unidirectional parallel grooves is studied for drop Weber number in the range 1–100 focusing on the role of texture geometry and wettability. The maximum spread factor of impacting drops measured perpendicular to grooves, βm,⊥ is seen to be less than that measured parallel to grooves, βm,∥. The difference between βm,⊥ and βm,∥ increases with drop impact velocity. This deviation of βm,⊥ from βm,∥ is analyzed by considering the possible mechanisms, corresponding to experimental observations(1) impregnation of drop into the grooves, (2) convex shape of liquid–vapor interface near contact line at maximum spreading, and (3) contact line pinning of spreading drop at the pillar edgesby incorporating them into an energy conservation-based model. The analysis reveals that contact line pinning offers a physically meaningful justification of the observed deviation of βm,⊥ from βm,∥ compared to other possible candidates. A unified model, incorporating all the above-mentioned mechanisms, is formulated, which predicts βm,⊥ on several groove-textured surfaces made of intrinsically hydrophilic and hydrophobic materials with an average error of 8.3%. The effect of groove-texture geometrical parameters on maximum drop spreading is explained using this unified model. A special case of the unified model, with contact line pinning absent, predicts βm,∥ with an average error of 6.3%.