Abstract
The apparent contact angle of Cassie-Baxter state water droplets can be calculated by the existing theoretical formula, but due to the defects of the micro-structured hydrophobic surface and some inevitable tiny disturbances in the experiment, Cassie-Baxter state water droplets will appear partly in Wenzel state, that is, the mixed state water droplets. In this paper, apparent contact angles of Cassie-Baxter state and mixed state water droplets on micro-structured hydrophobic surfaces are compared. The research shows that if the projected area fraction of water-solid F in the Cassie-Baxter formula is replaced by the local projected area fraction of water-solid F′, the apparent contact angles of water droplets in both Cassie-Baxter state and the mixed state can be calculated. Further experimental results indicate that the contact state of water droplets nearby the outermost three-phase contact line plays a more important role in determining the apparent contact angle. This conclusion is significant to the understanding of the apparent contact angle and wetting property.
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This work was supported by the National Natural Science Foundation of China (Grant Nos. 10672089 and 10872106).
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Yang, C., He, F. & Hao, P. The apparent contact angle of water droplet on the micro-structured hydrophobic surface. Sci. China Chem. 53, 912–916 (2010). https://doi.org/10.1007/s11426-010-0115-y
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DOI: https://doi.org/10.1007/s11426-010-0115-y