Hydrophobicity of textured aluminum surfaces

Abstract

Surfaces exhibiting hydrophobic characteristics are significant in both industrial and consumer applications. Considerable effort has gone into studying the hydrophobic properties of chemical coatings, nano and small machined structures, and naturally occurring surfaces. This study will test various simple textured aluminum surfaces that are easily reproducible and mechanically durable in order to determine the hydrophobicity of each surface. The relationships between contact angle and sliding angle, as well as surface roughness and contact angle hysteresis will also be examined. Six different surfaces were prepared, including a control surface, three surfaces of differing roughness, and two machined surfaces. The contact angle, sliding angle, and contact hystereses of the samples were analyzed, and the results were summarized and explained based on past research into drop-surface interaction. The highest contact angles measured were on the machined surfaces, with the control and abraded surfaces all exhibiting hydrophilic properties with the exception of one abraded surface. The data supports the notion that surface roughness does not strictly correlate with contact angle, as it is possible to roughen a surface in ways that increase contact angle.

The data also suggests that contact angle does not always correlate with sliding angle but surface roughness does correlate with sliding angle. The three roughest surfaces used in this experiment caused water drops to adhere to them so strongly that drops would not slide off of the surface, even when the surface was elevated to a completely vertical position. Lastly, drops placed on surfaces with large machined features (0.01”) were observed transitioning from the Cassie-Baxter state to the Wenzel state, suggesting that these features are too large or rough to allow the drops to remain in the Cassie-Baxter state for extended periods of time.