Wetting on nanoporous alumina surface: transition between Wenzel and Cassie states controlled by surface structure.
This paper reports a systematic study on the relationship between surface structure and wetting state of ordered nanoporous alumina surface. The wettability of the porous alumina is dramatically changed from hydrophilicity to hydrophobicity by increasing the hole diameter, while maintaining the hole interval and depth. This phenomenon is attributed to the gradual transition between Wenzel and Cassie states which was proved experimentally by comparing the wetting behavior on these porous alumina surfaces. Furthermore, the relationship between surface wettability and hole depth at a fixed hole interval and diameter was investigated. For those porous alumina with relatively larger holes in diameter, transition between Wenzel and Cassie states was also achieved with increasing hole depth. A capillary-pressure balance model was proposed to elucidate the unique structure-induced transition, and the criteria for the design and construction of a Cassie wetting surface was discussed. These structure-induced transitions between Wenzel and Cassie states could provide further insight into the wetting mechanism of roughness-induced wettability and practical guides for the design of variable surfaces with controllable wettability.
Ran
Chunbo
C
Unilever Research China, 99 Tianzhou Road, Shanghai, P. R. China. chun-bo.ran@unilever.com
Ding
Guqiao
G
Liu
Weichang
W
Deng
Yan
Y
Hou
Wentao
W
D000327:Adsorption; D000535:Aluminum / Q000737:chemistry*; D000537:Aluminum Oxide / Q000737:chemistry; D002627:Chemistry, Physical / Q000379:methods*; D008855:Microscopy, Electron, Scanning; D008956:Models, Chemical; D053758:Nanoparticles / Q000737:chemistry*; D012212:Rheology; D013499:Surface Properties; D014867:Water / Q000737:chemistry; D017155:Wettability
D014867:Water; D000535:Aluminum; D000537:Aluminum Oxide