Probing Microscopic Wetting Properties of Superhydrophobic Surfaces by Vibrated Micrometer-Sized Droplets

Alexandr Jonáš*, Yasin Karadag, Nevin Tasaltin, Ibrahim Kucukkara, and Alper Kiraz*
Department of Physics, Koç University, Rumelifeneri Yolu, 34450 Sariyer, Istanbul, Turkey
Langmuir, 2011, 27 (6), pp 2150–2154
DOI: 10.1021/la1049925
Publication Date (Web): January 31, 2011
Copyright © 2011 American Chemical Society
*E-mail: ajonas@ku.edu.tr (A.J.); akiraz@ku.edu.tr (A.K.).

Abstract

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We determine contact angles of micrometer-sized NaCl−water droplets on superhydrophobic surfaces by analyzing their lowest-order axisymmetric vibrational resonances driven by vertical oscillations of the surface. Fluorescence spectra of the dye-doped droplets excited by laser light feature whispering-gallery modes (WGMs) whose spectral widths depend on the droplet vibration amplitude, thus enabling precise measurements of the droplet mechanical resonant frequency. Following droplet size determination by WGM mode-matching, we calculate the contact angles from the dependence of the measured mechanical resonant frequency on the droplet size for two surfaces with different superhydrophobicity levels, and find a good correlation with the values measured by direct imaging of millimeter-sized droplets.

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    History

    • Published In Issue March 15, 2011
    • Article ASAPJanuary 31, 2011
    • Received: December 16, 2010
      Revised: January 18, 2011

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