Bioinspired hierarchical superhydrophobic structures formed by n-paraffin waxes of varying chain lengths

Nature demonstrates beautiful examples of superhydrophobic surfaces, which always exhibit hierarchical roughness. We demonstrate a simple biomimetic route to the formation of hierarchical roughness on paraffin wax surfaces by the successive deposition of waxes of increasing molecular weight (M-w). By means of this procedure the lower M-w waxes grow larger crystals, forming higher micro-roughness, the subsequently deposited higher M-w waxes produce lower submicron/nano-roughness, and the overall result is roughness of a higher hierarchical order. We show that, compared to unary wax crystal surfaces, these hierarchical structures have the advantage of increased surface stability expressed by the ability to maintain smaller drops in the Cassie-state, as well as the ability to support liquids having lower surface tensions with contact angles exceeding 150 degrees.