Properties of Superhydrophobic Surfaces made by RESS Technique

The properties of superhydrophobic [1, 2] surfaces produced by Rapid Expansion of Supercritical Solvent (RESS) were studied. These surfaces were produced on paper surfaces by spraying alkyl ketene dimer (AKD, a wax commonly used in paper industry) dissolved in SC-CO2 through a nozzle onto a moving paper substrate in ambient conditions [3, 4]. Pressure and temperature of the SC-CO2 were optimized, giving a pressure of 200 bar and a temperature of 65 ◦C. The speed of the substrate and the distance between the nozzle and the substrate were varied. The surfaces were studied with Scanning Electron Microscopy (SEM) and contact angle measurements to water. In the whole production parameter range the procedure resulted in a coating consisting of merged evenly sized flaky particles. A combination of high surface roughness and a hydrophobic material, as AKD, is important when creating a superhydrophobic surface [1,2]. The spraying distance showed to be of importance, with distances below 60 mm giving complete surface coverage while distances above 100 mm giving an incomplete surface coverage. The developed method is robust and repeatable, giving surfaces with water contact angles above 160 ◦.