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A Combinatorial Library of Micro‐Topographies and Chemical Compositions for Tailored Surface Wettability
Author(s) -
Kolind Kristian,
Bennetsen Dines Tilsted,
Arpanaie Ayyoob,
Duch Mogens,
Lovmand Jette,
Besenbacher Flemming,
Kingshott Peter,
Foss Morten
Publication year - 2011
Publication title -
advanced engineering materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.938
H-Index - 114
eISSN - 1527-2648
pISSN - 1438-1656
DOI - 10.1002/adem.201000318
Subject(s) - contact angle , wetting , x ray photoelectron spectroscopy , materials science , pillar , nanotechnology , wafer , silane , silicon , surface modification , chemical engineering , composite material , optoelectronics , mechanical engineering , engineering
Surface modification of topography and chemistry in order to achieve a specific water contact angle (CA) has been explored by using a novel combinatorial screening platform. The screening arrays consisted of 507 distinct combinations of micro‐topographies and chemical compositions. By performing chemical modifications with 1H, 1H, 2H, 2H perfluoroethyltriethoxy‐silane (PFS) and n‐octadecyltriethoxysilane (ODS) on standard silicon wafers it was possible to include both superhydrophobic and very hydrophilic pad arrays in the same screening platform. Surfaces modified with PFS were more hydrophobic than surfaces modified with ODS, while the unmodified silicon surfaces were hydrophilic. For the PFS modified surfaces the largest CAs were achieved with a small pillar size of X = 1 µm and an intermediate inter‐pillar gap size of Y = 4 µm with superhydrophobic CAs over 170°. Surface analysis with X‐ray photoelectron spectroscopy (XPS) revealed that CF 3 groups were present at the surface, contributing to the superhydrophobic effect. The ODS modified surfaces had intermediate wettabilities with CAs between 100 and 150°, which were dependent on the pillar size, the inter‐pillar gap size, and the specific pillar pattern. The unmodified silicon topographical surfaces were very hydrophilic with CAs below 20° independent of specific topography. With this approach we have managed to fabricate 507 distinct surface areas covering a range of wettabilities, which is useful when screening these effects in several different applications. The measured CAs did not follow the simple Wenzel model. Furthermore, the adaptation of the Cassie model introduces Φ s , the fraction of solid surface in contact with the liquid, which is difficult to estimate, thereby emphasizing the need for an experimental determination.