Issue 13, 2012
From the journal:

Soft Matter

Modulation of surface wettability of superhydrophobic substrates using Si nanowire arrays and capillary-force-induced nanocohesion†

M. K. Dawood,a   H. Zheng,a   N. A. Kurniawan,b   K. C. Leong,c   Y. L. Foo,d   R. Rajagopalan,be   S. A. Khanbe  and  W. K. Choi*af  

* Corresponding authors

a Department of Electrical and Computer Engineering, National University of Singapore, Singapore

b Department of Chemical and Biomolecular Engineering, National University of Singapore, Singapore

c GLOBALFOUNDRIES Singapore Pte. Ltd, Singapore

d Institute of Materials Research and Engineering, A*STAR (Agency for Science, Technology, and Research), Singapore

e Chemical and Pharmaceutical Engineering Programme, Singapore-MIT Alliance, Singapore

f Advanced Materials for Micro- and Nano-Systems Programme, Singapore-MIT Alliance, Singapore
E-mail: elechoi@nus.edu.sg

Abstract

We describe a new scalable method to fabricate large-area hybrid superhydrophobic surfaces with selective adhesion properties on silicon (Si) nanowire array substrates by exploiting liquid-medium-dependent capillary-force-induced nanocohesion. Gold (Au) nanoparticles were deposited on Si by glancing angle deposition followed by metal-assisted chemical etching of Si to form Si nanowire arrays. The surfaces were dried in either deionized (DI) water, 2-propanol or methanol to vary the capillary forces exerted on the Si nanowires during the drying process in order to tune the extent of clustering of nanowires and hence the adhesion properties of the resulting superhydrophobic surfaces. Here, we exploit the combined effects of surface tension and Young's contact angle to modulate the degree of clustering of the Si nanowires during capillary-force-induced nanocohesion. These surfaces were chemically modified and rendered hydrophobic by fluorosilane deposition. Drying in DI water resulted in small clusters of nanowires which produce a low-hysteresis superhydrophobic surface that mimics a lotus leaf. Drying in methanol resulted in large nanowire clusters that lead to a high-hysteresis superhydrophobic surface. Further, we demonstrate the ability to fabricate both small and large nanowire clusters by controlling the drying of the nanowire arrays in order to selectively define and modulate adhesion of water on the same superhydrophobic substrate. The simplicity of our process to tune surface wettability on single substrates paves the way for future applications in lab-on-chip devices and platforms for chemical and biological analyses.

Graphical abstract: Modulation of surface wettability of superhydrophobic substrates using Si nanowire arrays and capillary-force-induced nanocohesion

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Article information

DOI
https://doi.org/10.1039/C2SM07279C
Article type
Paper
Submitted
01 Dec 2011
Accepted
05 Jan 2012
First published
14 Feb 2012

Soft Matter, 2012,8, 3549-3557

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Modulation of surface wettability of superhydrophobic substrates using Si nanowire arrays and capillary-force-induced nanocohesion

M. K. Dawood, H. Zheng, N. A. Kurniawan, K. C. Leong, Y. L. Foo, R. Rajagopalan, S. A. Khan and W. K. Choi, Soft Matter, 2012, 8, 3549 DOI: 10.1039/C2SM07279C

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