Wetting Transition Characteristics on Microstructured Hydrophobic Surfaces

Hydrophobicity and wetting transition behavior of water droplets were nu, emulated 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 mu m, height 150 mu m) with varying spacing-to diameter ratio (s/d) ranging from similar to 1 0 to similar to 3 3 A deionized(DI) water droplet of 4 3 mu l 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 similar to 1 81 to similar to 2 95 In the transition regime a partial penetration at liquid meniscus which Moses downward in the groove formed by foul 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 [doi 10 2320/matertrans M2010118)