Fatty acid monolayers on randomly nanostructured inorganic surfaces: Interplay of wettability, chemistry and topography

Abstract

Understanding the wetting properties of chemically-modified inorganic surfaces with random nanoscale topography is of fundamental importance for diverse applications. This issue has hitherto continuously been the subject of considerable controversies. Herein, we report a thorough investigation of the wettability-topography-chemistry balance for a surface with random nanoscale topography, the main challenge being decoupling topography from surface chemistry. For this purpose, we use a superficially nanostructured aluminum substrate chemically modified by fatty acid monolayers. From AFM data, we extract a variety of parameters describing the surface topography by means of variogram calculations, a method originally developed by geo-statists to explore large surfaces. Moreover, by using a power transform approach, we establish a consistent relationship relating wettability, topography and surface chemistry. Interestingly, we demonstrate that the water contact angle comprises a contribution due to the surface composition, originating from hydrophilization through alkyl chains, and a contribution due to the surface topography. This model is valid in the Wenzel region, and may suggest ways to tune the wetting properties of inorganic surfaces with nanoscale stochastic topographies