Drop mobility on superhydrophobic microstructured surfaces with wettability contrasts

Yutaku Kita, Coinneach Mackenzie Dover, Alexandros Askounis, Yasuyuki Takata, Khellil Sefiane

Research output: Contribution to journalArticlepeer-review

21 Scopus citations

Abstract

Manipulation of drop motion has attracted considerable attention recently as it is pertinent to industrial/biological applications such as microfluidics. Wettability gradients/contrasts applied to microtextured, superhydrophobic surfaces are probable candidates for engineering drop motion by virtue of their wettability controllability and low contact angle hysteresis. In the present work, we present a systematic study of drop mobility induced via wettability contrasts. A millimetre-sized water drop, placed on the boundary between two surfaces with distinct, uniform arrays of pillars, immediately moved toward the surface more densely populated with asperities, which was relatively more hydrophilic. The velocity of the motion was found to increase proportionally with the difference in pillar densities on each surface, in circumstances where the rear side surface had sufficiently small contact angle hysteresis. To elucidate the underlying mechanism of drop motion, we implemented a surface energy analysis for each motion event. Motion was initiated by the excess surface free energy due to drop deformation and directed in favour of energy minimisation. Lastly, we propose a theory to predict the direction of the drop which at the same time acts as the criterion for the motion to ensue.

Original languageEnglish (US)
Pages (from-to)9418-9424
Number of pages7
JournalSoft Matter
Volume14
Issue number46
DOIs
StatePublished - 2018
Externally publishedYes

Bibliographical note

Funding Information:
We gratefully acknowledge Dr Prashant Valluri of the University of Edinburgh for his suggestions for the energy analysis. The surface coatings used in this work were provided by MEMSstar Ltd. This work was supported by the Japan Society for the Promotion of Science (JSPS) KAKENHI Grant Number 17J05137.

Publisher Copyright:
© The Royal Society of Chemistry.

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