Bubble formation on superhydrophobic-micropatterned copper surfaces

Surface physicochemical properties, including wettability and micro-nanoscopic roughness, play an important role in boiling heat transfer and interfacial phenomena. In the paper, we report investigation on bubble formation over superhydrophobic-micropatterned copper surfaces. The distinctive non-wetting micropatterns (of 180 x 180 mu m(2) squares) were fabricated by our recently reported stereomask lithography process, using a novel superhydrophobic nanocomposite formulation. The superhydrophobic nanocomposite, comprised of polytetrafluoroethylene (PTFE) nanoparticles (of 250 nm in diameter) in a polymeric matrix, presented high degree of hydrophobicity (with water contact angle > 150 degrees). Standard boiling processes were studied with or without a prior-degassing procedure, experimentally. In addition, experiments on uniform superhydrophobic coating as well as bare copper surfaces were conducted as control. The experimental investigations revealed that the micropattern-coated copper surfaces had low bubble formation temperatures, similar to the uniformly coated superhydrophobic surfaces; and those emerging bubbles were more spherical and less likely to merge into a vapor layer. (C) 2011 Elsevier Ltd. All rights reserved.