Questions and Answers on the Wettability of Nano‐Engineered Surfaces

Surface roughening has long been used to confer materials remarkable wetting properties, such as super hydrophobicity. When roughness belongs to the microscale, existing models can, to some extent, explain and predict real‐world wetting states. With the advent of nanotechnology, however, a multitude of nano‐engineered materials are being developed and unexpected wetting behaviors have been observed which cannot be described by conventional theories. While it is clear that advanced nanotextured materials are essential to a vast range of ground breaking technologies, the intricate mechanisms governing the wetting of such surfaces—at the limit of validity of continuum theories—also need to be clarified. This review aims at presenting what is known and what remains to be discovered about the wettability of nanoengineered materials. The advantages and uniqueness of nanostructured substrates is highlighted first, with a focus on practical applications benefitting from the distinctive wetting properties of nanorough substrates. Classic wetting theories and their limitations are briefly discussed, before describing with a top down vision, why the wetting of nanostructured substrates differ from that of microtextured surfaces. Recent experimental and theoretical studies which contributed to the progress in this field are considered, before outlining potential future areas of research.