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Applied Physics Letters / Volume 97 / Issue 23 / INTERDISCIPLINARY AND GENERAL PHYSICS

Appl. Phys. Lett. 97, 234102 (2010); http://dx.doi.org/10.1063/1.3524513 (3 pages)

Frost formation and ice adhesion on superhydrophobic surfaces

Kripa K. Varanasi1, Tao Deng2, J. David Smith1, Ming Hsu2, and Nitin Bhate2

1Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
2Nanotechnology Advanced Technology, GE Global Research Center, Niskayuna, New York 12309, USA

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(Received 25 October 2010; accepted 7 November 2010; published online 7 December 2010)

We study frost formation and its impact on icephobic properties of superhydrophobic surfaces. Using an environmental scanning electron microscope, we show that frost nucleation occurs indiscriminately on superhydrophobic textures without any particular spatial preference. Ice adhesion measurements on superhydrophobic surfaces susceptible to frost formation show increased adhesion over smooth surfaces with a strong linear trend with the total surface area. These studies indicate that frost formation significantly compromises the icephobic properties of superhydrophobic surfaces and poses serious limitations to the use of superhydrophobic surfaces as icephobic surface treatments for both on-ground and in-flight applications.

© 2010 American Institute of Physics

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KEYWORDS and PACS

Keywords

adhesion, hydrophobicity, ice, nucleation, scanning electron microscopy, solid-liquid transformations

PACS

  • 64.70.D-

    Solid-liquid transitions

  • 64.60.qj

    Studies of nucleation in specific substances

  • 68.35.Np

    Adhesion

  • 68.37.Hk

    Scanning electron microscopy (SEM) (including EBIC)

ARTICLE DATA

Digital Object Identifier
http://dx.doi.org/10.1063/1.3524513

PUBLICATION DATA

ISSN

0003-6951 (print)  
1077-3118 (online)

Publisher

$abstract.society.value is a Member of CrossRef American Institute of Physics

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    References

    K. K. Varanasi, M. Hsu, N. Bhate, W. Yang, and T. Deng, Appl. Phys. Lett. 95, 094101 (2009)APPLAB000095000009094101000001.

    T. Deng, K. K. Varanasi, M. Hsu, N. Bhate, C. Keimel, J. Stein, and M. Blohm, Appl. Phys. Lett. 94, 133109 (2009)APPLAB000094000013133109000001.


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Figures (click on thumbnails to view enlargements)

FIG.1
ESEM images of frost formation on a superhydrophobic surface comprising of an array of hydrophobic square posts with width, edge-to-edge spacing, and aspect ratio of 15 μm, 30 μm, and 7, respectively. (a) Dry surface. [(b)–(d)] Snapshot images of frost formation on the surface. The intrinsic water contact angle of the hydrophobic coating on the posts is ∼ 110°. The surface is maintained at a temperature −13 °C by means of a cold stage accessory of the ESEM. At the beginning of the experiment the chamber pressure is maintained at ∼ 100 Pa, well below the saturation pressure to ensure a dry surface. The vapor pressure in the chamber is then slowly increased until frost nucleation is observed. Frost nucleation and growth occurs without any particular spatial preference on all of the available area including post tops, sidewalls, and valleys due to the uniform intrinsic wettability of the surface.

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FIG.2
Droplet impact measurements on dry and frosted superhydrophobic surface conducted using droplets of 1 mm radius impacting the surface at velocity ∼ 0.7 m/s. (a) Top view SEM image of the representative Si post array surface with width, edge-to-edge spacing, and aspect ratio of 10 μm, 20 μm, and 1, respectively. (b) Photograph of the dry surface along with sequential high-speed video images of droplet impact. As expected, droplet recoils from the surface, as the antiwetting capillary pressure is greater than the dynamic wetting pressures (see Ref. 25). (c) Photograph of the frosted surface along with sequential high-speed video images of droplet impact. Frost alters the wetting properties of the surface, making the surface hydrophilic, causing Cassie-to-Wenzel wetting transition of the impacting drop, subsequent pinning and formation of “Wenzel” ice on the surface.

FIG.2 Download High Resolution Image (.zip file) | Export Figure to PowerPoint

FIG.3
Plot of the measured ice adhesion strength of the textured surfaces normalized by the measured ice adhesion strength of the smooth surface as a function of total surface area normalized by the projected area. The ice adhesion measurements on textured and smooth PDMS surfaces were conducted at −15 °C using the apparatus described in supplementary material (Ref. 17). The normalized ice adhesion strength increases with normalized surface area and shows a strong linear trend. The best linear fit to the data (solid line, correlation coefficient R2 = 0.96) has a slope of one and passes through the origin (extrapolated using a dashed line) indicating that ice is contacting all available surface area. Insets [(a)–(d)] are top view optical images of representative replicated PDMS post arrays from sparse to dense spacing (a = 15 μm, h = 10 μm, b = 45, 30, 15, and 5 μm, respectively) showing the excellent quality of replication.

FIG.3 Download High Resolution Image (.zip file) | Export Figure to PowerPoint

Supplemental Files (EPAPS)



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