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Droplets Jumping from a Hybrid Superhydrophilic and Superhydrophobic Surface

[+] Author and Article Information
Hai Wang

Department of Mechanical and Aerospace Engineering, University of Missouri, Columbia, MO, USA
hwtwb@mail.missouri.edu

Quang Nguyen

Department of Electrical and computer engineering, University of Missouri, Columbia, MO, USA
qtn5zf@mail.missouri.edu

Jae W. Kwon

Department of Electrical and computer engineering, University of Missouri, Columbia, MO, USA
kwonj@missouri.edu

Jing Wang

Department of Mechanical and Aerospace Engineering, University of Missouri, Columbia, MO, USA
WaJing@missouri.edu

Hongbin Ma

Department of Mechanical and Aerospace Engineering, University of Missouri, Columbia, MO, USA
mah@missouri.edu

1Corresponding author.

J. Heat Transfer 139(2), 020908 (Jan 06, 2017) Paper No: HT-16-1720; doi: 10.1115/1.4035578 History: Received November 04, 2016; Revised December 06, 2016

Abstract

The wetting condition effect of the condensation process on a hybrid superhydrophobic and superhydrophilic copper surface as shown in Fig. 1a was experimentally investigated. The superhydrophilic surface (Fig. 1b) consists of micro-flowers (CuO) and nanorods (Cu(OH)2) obtained by immersing the copper substrate into alkaline solution of 2.5 M sodium hydroxide and 0.1 M ammonium persulphate, and the superhydrophobic nanostructured surface (Fig. 1c) was formed by spin coating the Cytop on the hierarchically structured CuO / Cu(OH)2 surface. Experimental results show that the film condensation started on the superhydrophilic region while the dropwise condensation of tiny droplets with an average contact angle of 160° were formed on the superhydrophobic region. Because the film condensation was confined within the superhydrophilic region of 1 mm x 1 mm, the contact angle of this droplet became larger and larger. When a tiny droplet developed on the superhydrophobic area joins with the big droplet formed on the superhydrophilic surface (square region), the coalesced droplet obtains additional energy and jumps off from the condensing surface.

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