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access icon free Photoresponsive wettability switching of TiO2-coated micropillar arrays with different geometries of overhang roofs

  • Author(s): Taizo Kobayashi 1 ; Hironobu Maeda 2 ; Satoshi Konishi 1, 3
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  • Source: Volume 12, Issue 8, August 2017, p. 540 – 544
    DOI:  10.1049/mnl.2017.0121 , Online ISSN 1750-0443
© The Institution of Engineering and Technology
Received 24/02/2017, Accepted 27/04/2017, Revised 15/04/2017, Published 01/08/2017

In this work, micropillar array structures with overhang roofs which increase the switching range of the TiO2 photoresponsive wettability, have been fabricated. The liquid droplet placed on the micropillar array exhibits the Cassie–Baxter superhydrophobic state because of the receding of the liquid–air interface to the pillar top, when its contact angle (θ TiO2) on the TiO2 surface exceeds than the geometrical angle (ψ) between the overhang roof and the vertical micropillar shaft. The Cassie–Baxter state can be transformed into the Wenzel state at a relatively large surface area of the micropillar array when the magnitude of θ TiO2 becomes smaller than ψ after ultraviolet irradiation due to the photoinduced superhydrophilicity of TiO2. The rutile TiO2-coated micropillar array with a small ψ exhibits faster reverse wettability transformation from the Wenzel state to the Cassie–Baxter state despite the relatively small θ TiO2 increase in the dark. In addition, the wettability reversal time was shortened from 180 to 6 min after decreasing ψ from 51° to 9°.

Inspec keywords: ultraviolet radiation effects; contact angle; hydrophilicity; titanium compounds; wetting; hydrophobicity; drops

Other keywords: contact angle; TiO2; photoinduced superhydrophilicity; liquid-air interface; rutile micropillar array; geometrical angle; reverse wettability transformation; overhang roofs; ultraviolet irradiation; photoresponsive wettability switching; Cassie-Baxter superhydrophobic state; surface area; liquid droplet; Wenzel state; vertical micropillar shaft

Subjects: Fluid interface activity, spreading; Ultraviolet, visible and infrared radiation effects; Fluid surface energy (surface tension, interface tension, angle of contact, etc.)

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