August 1, 2014.
Superamphiphobic surfaces strongly repel both water and oils. In this work, aluminum coupons are processed by sanding with various grit of sand paper to impart microscale roughness. Subsequent submersion of the aluminum substrate in boiling water grows nanoscale grass-like structures. The oxide layer of Al is slightly soluble in water. During a fast diffusion/equilibrium, Al2O3 nanograss grows on the surface. A low energy coating is then deposited on the surface. The micro and nanoscale features create re-entrant structures that trap air enabling contact liquid to be in a Cassie-Baxter state. Superamphiphobicity of the samples were confirmed by appearance of a reflective plastron on the surface while submerged in water. The SAP surfaces were placed in a water flow cell to assess the heat transfer characteristics under flow by measuring their cooling rate. An air layer should eliminate the zero velocity boundary layer between a flowing liquid and a surface. Increased flow at a surface enabled by a plastron (a thin air layer) could increase the rate of heat transfer. The demonstration of this particular work can be applied throughout various daily life materials, such as: cars, clothes, rooftops, umbrellas, and rocket engines.
Analytical Chemistry | Atomic, Molecular and Optical Physics | Engineering Physics | Fluid Dynamics | Physical Chemistry | Thermodynamics
Jeffrey Alston and Andrew Guenthner
Air Force Research Laboratory (AFRL)
This material is based upon work supported by the S.D. Bechtel, Jr. Foundation and by the National Science Foundation under Grant No. 0952013 and Grant No. 0833353. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the S.D. Bechtel, Jr. Foundation or the National Science Foundation. This project has also been made possible with support of the National Marine Sanctuary Foundation. The STAR program is administered by the Cal Poly Center for Excellence in Science and Mathematics Education (CESaME) on behalf of the California State University (CSU).