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Liquid spreading on superhydrophilic micropillar arrays

Published online by Cambridge University Press:  20 June 2011

SEONG JIN KIM ,
MYOUNG-WOON MOON ,
KWANG-RYEOL LEE ,
DAE-YOUNG LEE ,
YOUNG SOO CHANG  and
HO-YOUNG KIM
SEONG JIN KIM
Affiliation:
School of Mechanical and Aerospace Engineering, Seoul National University, Seoul 151-744, Korea
MYOUNG-WOON MOON
Affiliation:
Korea Institute of Science and Technology, Seoul 136-791, Korea
KWANG-RYEOL LEE
Affiliation:
Korea Institute of Science and Technology, Seoul 136-791, Korea
DAE-YOUNG LEE
Affiliation:
Korea Institute of Science and Technology, Seoul 136-791, Korea
YOUNG SOO CHANG
Affiliation:
Department of Advanced Fermentation Fusion Science and Technology, Kookmin University, Seoul 136-702, Korea
HO-YOUNG KIM*
Affiliation:
School of Mechanical and Aerospace Engineering, Seoul National University, Seoul 151-744, Korea
*
†Email address for correspondence: hyk@snu.ac.kr
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Abstract

When a drop is deposited on a superhydrophilic micropillar array, the upper part of the drop (referred to as the bulk) collapses while the bottom part penetrates into the gaps of the array, forming a fringe film. Here we quantify the early stage dynamics of this process using a combination of experiment and theory. We show that the circular front of the fringe film spreads like t1/2, t being time, when coupled to the bulk flow. However, the film is found to advance like t1/3 through faceted zippering in the absence of the bulk. We then show that the spreading of the bulk and the entire drop footprint follows a power law (t1/4) that is different from Washburn's law. This work can be a starting point to completely understand the spreading of liquids on superhydrophilic surfaces and opens questions specific to superwetting behaviour including the criteria to determine whether the fringe film will expand through lateral zipping or advance radially outwards.

JFM classification

Interfacial Flows (free surface): Capillary flows Micro-/Nano-fluid dynamics: Microfluidics Interfacial Flows (free surface): Thin films
Type
Papers
Information
Journal of Fluid Mechanics , Volume 680 , 10 August 2011 , pp. 477 - 487
Copyright
Copyright © Cambridge University Press 2011

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