Lotus-Effect®: Biomimetic Super-Hydrophobic Surfaces and their Application

Abstract

The majority of organismic surfaces, like the plant cuticle, is not smooth but micro-structured. Moreover, they are often covered with hydrophobic wax crystals, some hundred nm in size. The combination of micro- and nanostructures, together with a hydrophobic chemistry, generates the phenomenon of super-hydrophobicity: Water-droplets on such surfaces exhibit contact angles above 140°. Furthermore, dirt particles can barely adhere and are removed by running water only, hence they are called ‘self-cleaning’. The underlying physico-chemical principles were successfully applied to technical prototypes. This technical conversion was patented and the trade mark Lotus-Effect® was introduced in the mid 1990s. Since then several Lotus-Effect® products like a façade paint, a glass coating or a spray were introduced. Another area of application for which prototypes exist, are textiles for awnings, tents or other outdoor purposes. Recently a different aspect of such surfaces is investigated: structures retaining air under water. Several floating plants and semiaquatic animals show this ability. The aim of this project is to develop technical surfaces for long time application in ships and pipelines, as an air film between surface and liquid leads to drag reduction and thus savings of energy.