Anisotropic wetting characteristics on submicrometer-scale periodic grooved surface

Zhao, Yan, Lu, Qinghua, Li, Mei and Li, Xin 2007, Anisotropic wetting characteristics on submicrometer-scale periodic grooved surface, Langmuir, vol. 23, no. 11, pp. 6212-6217, doi: 10.1021/la0702077.

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Title Anisotropic wetting characteristics on submicrometer-scale periodic grooved surface
Author(s) Zhao, Yan
Lu, Qinghua
Li, Mei
Li, Xin
Journal name Langmuir
Volume number 23
Issue number 11
Start page 6212
End page 6217
Publisher American Chemical Society
Place of publication Washington D. C.
Publication date 2007-04-28
ISSN 0743-7463
Summary Submicrometer-scale periodic structures consisting of parallel grooves were prepared on azobenzene-containing multiarm star polymer films by laser interference. The wetting characteristics on the patterned surfaces were studied by contact angle measurements. Macroscopic distortion of water drops was found on such small-scale surface structures, and the contact angles measured from the direction parallel to the grooves were larger than those measured from the perpendicular direction. A thermodynamic model was developed to calculate the change in the surface free energy as a function of the instantaneous contact angle when the three-phase contact line (TPCL) moves along the two orthogonal directions. It was found that the fluctuations, i.e., energy barriers, on the energy versus contact angle curves are crucial to the analysis of wetting anisotropy and contact angle hysteresis. The calculated advancing and receding contact angles from the energy versus contact angle curves were in good agreement with those measured experimentally. Furthermore, with the groove depth increasing, both the degree of wetting anisotropy and the contact angle hysteresis perpendicular to the grooves increased as a result of the increase in the energy barrier. The theoretical critical value of the groove depth, above which the anisotropic wetting appears, was determined to be 16 nm for the grooved surface with a wavelength of 396 nm. On the other hand, the effect of the groove wavelength on the contact angle hysteresis perpendicular to the grooves was also interpreted on the basis of the thermodynamic model. That is, with the wavelength decreasing, the contact angle hysteresis increased due to the increase in the number of energy barriers. These results may provide theoretical evidence for the design and application of anisotropic wetting surface.
Language eng
DOI 10.1021/la0702077
Field of Research 091209 Polymers and Plastics
HERDC Research category C1.1 Refereed article in a scholarly journal
Copyright notice ©2007, American Chemical Society
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