US EPA

738618 

Journal Article 

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

Jonáš, A; Karadag, Y; Tasaltin, N; Kucukkara, I; Kiraz, A 

2011 

1 

Langmuir
ISSN: 0743-7463
EISSN: 1520-5827 

27 

6 

2150-2154 

English 

21280575 

10.1021/la1049925 

https://pubs.acs.org/doi/10.1021/la1049925
Exit
 

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.