Assessing durability of superhydrophobic surfaces

Superhydrophobic surfaces (SHS) show remarkable water repellency properties, and their use may have a tremendous impact for a plethora of applications, where liquid water accumulation needs to be controlled or minimised. However, the durability of SHS in operational conditions is a severe issue that currently represents a bottleneck for the technology transfer from laboratory to industrial applications. In the present work, we try to fill in the gap caused by the absence of a standard for evaluation for SHS durability, by developing a protocol for testing surface durability. The proposed protocol includes nine tests as follows: water immersion, acidic environment, alkaline environment, ionic solution, mechanical erosion, ultraviolet exposure, resistance to heating, alcohol immersion and hydrocarbon immersion. The protocol can serve to give an indication of surface robustness in a variety of potentially harmful environments, by providing a global figure of merit and ranking for different SHS and thereby allowing for identifying those surfaces fulfilling requirements for a specific application. To illustrate the protocol, we tested a SHS developed in-house by grafting of lauric acid molecules on an aluminum substrate.