Metallic hydrophobic surface fabrication and wettability study

Cui, Cong (2018) Metallic hydrophobic surface fabrication and wettability study. Masters thesis, Memorial University of Newfoundland.

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Abstract

Hydrophobic surfaces can be designed to have useful properties such as self-cleaning, anti-icing, and flow drag reduction. Research interests in this area have been growing with rising demands from various industries. Hydrophobic surfaces can be fabricated by coating, micro or nano-scale texturing, or a combination of the two. For industrial applications, methods for mass production of hydrophobic surfaces are desired. This thesis investigated two hydrophobic surface fabrication methods, laser machining and sandblasting, and conducted wettability analysis of the fabricated surfaces. In the laser machining, four microscale surface structures including channel, pillar, varied channel and varied pillar, are designed and fabricated. The static contact angles of all laser-machined samples are close to 130° without any coating. In sandblasting fabrication, three standoff distances (10 mm, 20 mm and 30 mm) between the spray nozzle and target surfaces are tested. For stainless steel, lower standoff distance leads to increased water contact angle on the sandblasted surfaces. For carbon steel, sandblasting increases wettability of the carbon steel, with lower contact angle from lower standoff distance. A low energy coating (Aculon) is applied on the samples from both fabrication methods. In the analysis, samples are divided into two groups, one for coated samples, and the other for the uncoated ones. Overall, the coating increases static contact angle and decreases hysteresis in all laser-machined samples and sandblasted ones. The difference in wettability of the samples from the two fabrication methods is analyzed in details. Sandblasted samples can reach 113°±4° without any coating, compared with static contact angle of 128°±5° from the laser-machined sample with pillar. After coating, the water contact angle of sandblasted samples increases to 137°±3° compared with 142°±4° on laser machined samples with pillar. The results of contact angle hysteresis are nearly same for the two methods before coating. After coating, contact angle hysteresis on sandblasted samples is overall lower than that on laser-machined samples.

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