The Design of Water Repellent Stainless Steel Surfaces

The design of liquid repellent surfaces has attracted much attention due to the potential for self-cleaning, drag reduction, or anti-corrosion applications. Despite recent significant developments, relatively few studies have been reported on the creation of liquid repellent metal and metal alloy surfaces. In this presentation, we discuss a method to control the surface topography of stainless steel by electrochemical methods. A dilute nitric acid electrolyte was used to alter the relative rates of grain boundary and metal grain etching, which is the key factor in establishing and controlling the micro-scale structure on stainless steel. The etch selectivity between grains and grain boundaries was controlled by the bias potential applied to the stainless steel, thereby permitting variation of the surface topography. With the application of a low potential (1.0V), high selectivity between grain and grain boundary etching was achieved, which resulted in significant grain boundary etching. As the potential was increased, etch selectivity decreased and ultimately generated smooth, electro-polished surfaces. Using contact angle measurements, the wetting behavior of etched stainless steel surfaces was determined and related to the specific structures and topography created by the electrochemical treatments.