Materials Transactions Online

Materials Transactions, Vol.51 No.09 (2010) pp.1709-1711
© 2010 The Japan Institute of Metals

Wetting Transition Characteristics on Microstructured Hydrophobic Surfaces

Jae Bong Lee, Hyuk Rok Gwon, Seong Hyuk Lee and Minhaeng Cho

School of Mechanical Engineering, Chung-Ang University, Seoul 156-756, Korea

Hydrophobicity and wetting transition behavior of water droplets were investigated on microstructured hydrophobic rough surfaces with pillar arrays, fabricated by self-replication with hydrophobic polydimethylsiloxane(PDMS) together with the use of CNC machine. The surfaces consist of microscale pillars(diameter: 105 μm, height: 150 μm) with varying spacing-to-diameter ratio (s/d) ranging from ∼1.0 to ∼3.3. A de-ionized(DI) water droplet of 4.3 μl was placed on hydrophobic surfaces and contact angles(CA) were measured by the digital image processing algorithm. A wetting transition from the Cassie state to the Wenzel state was demonstrated depending on the values of s/d, from ∼1.81 to ∼2.95. In the transition regime, a partial penetration of liquid meniscus which moves downward in the groove formed by four pillar posts was observed. It was also found that the contact angle prediction using the Cassie-Baxter equation showed fairly good agreement with experimental data, whereas in the transition regime, the rapid decrease in CA was found.

(Received 2010/4/6; Accepted 2010/6/3; Published 2010/7/14)

Keywords: hydrophobic surface, wetting transition, droplet, pillar array, Cassie-Baxter, Wenzel

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