New insights on contact angle/roughness dependence on high surface energy materials

The relationship between wettability and roughness has been studied on micro-roughened titanium surface after different cleaning procedures. Whereas most studies addressing (super)-hydrophobic behaviors have so far dealt with the wetting of low surface energy and textured substrates in air environment, we here report on a totally novel system and configuration involving the wetting of highly hydrophilic, textured metallic materials in liquid alkane medium, the so-called two liquid phase method. Roughness characterization showed that substrates were isotropic (2D), at a lengthscale much smaller than the size of the drop, with a heterogeneous (vertical) distribution of peaks and valleys. Depending on whether the alkane that initially penetrates and resides in the pores is displaced or not by the water drop (as for air pockets in air environment), we show that different wetting regimes may appear, depending on the cleaning procedure. To our knowledge, this is the first systematic study dealing with the interplay between surface roughness, the wetting behavior and in particular the (super)-hydrophilicity of high surface energy substrates, in non water miscible liquid environments. Whenever competitive processes of liquid/liquid displacement are involved at such high surface energy and textured substrates, such as titanium implant in bone tissue, these results may contribute understanding and predicting their wetting behavior. (C) 2011 Elsevier B. V. All rights reserved.