The resistance of a number of transparent hydrophobic surfaces to fouling by water, soils, and insects was studied as a function of accelerated weathering exposure time. Weathering-induced changes in the chemical composition of the surfaces were quantified via x-ray photoelectron spectroscopy (XPS) and water contact angle measurements. A decrease in fluorine content at the surface was correlated with reduced water contact angle and reduced resistance to fouling. Fouling resistance was assessed via a custom-built test stand that enabled the reproducible application of different foulants. Image analysis via the structural similarity index measure (SSIM) of a static target imaged through the transparent surface was used to quantify the resistance to fouling. Prescribed cleaning cycles with water and forced air were then used to assess the surfaces’ cleanability, again via changes in the SSIM. Cleanability was found to be largely correlated to the surfaces’ static contact angle with water. However, heterogeneous degradation of some surfaces during weathering resulted in pinning of some water droplets in degraded regions of the surface. Fouling by insects was evaluated by impacting house flies (<i>Musca domestica</i>) against the surfaces using an air assisted launching system. Insect fouling resistance and cleanability were assessed by changes in the SSIM after each step in the fouling and cleaning process. Assessments of this type were used to inform design choices for autonomous vehicle (AV) sensors.

Fouling and cleanability of transparent functional surfaces

ACS Fall 2021

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