In situ, noninvasive characterization of superhydrophobic coatings

Abstract

Light scattering was used to measure the time-dependent loss of air entrapped within a submerged microporous hydrophobic surface subjected to different environmental conditions. The loss of trapped air resulted in a measurable decrease in surface reflectivity and the kinetics of the process was determined in real time and compared to surface properties, such as porosity and morphology. The light-scattering results were compared with measurements of skin-friction drag, static contact angle, and contact-angle hysteresis. The in situ, noninvasive optical technique was shown to correlate well with the more conventional methods for quantifying surface hydrophobicity, such as flow slip and contact angle.

Polymeric Slippery Coatings: Nature and Applications

“…Similar to the case of microfabricated surfaces, fibrous coatings can provide the porosity that is necessary to entrap air when the surface is immersed in water. When water flows over such a surface, a reduction in skin friction is observed [20]. Two recent reviews [68,69] discussed several techniques to develop superhydrophobic and oleophobic fibrous surfaces using electrospinning methods.…”

“…Samaha et al [20] developed an optical technique to measure the longevity of submerged superhydrophobic coatings subjected to different environmental conditions. They used an optical spectroscopy system to quantify the intensity of reflected light in the visible range scattered from the surface (Figure 34).…”

“…The segmentation process was performed using Ostu's algorithm [103] in which the gray levels of the original image are split into two classes at the optimum thresholding value at which the intra-class variance of both classes is minimal. The stability of the meniscus (air-water interface) was evaluated by measuring the pressure needed for wetting transition using a developed optical technique and a custom-built pressure vessel [20], which is explained in the next sub-subsection. The degree of hydrophobicity of the coatings was characterized via goniometer measurements of the static contact-angle as well as contact-angle hysteresis.…”

“…As long as air pockets are entrapped in the surface pores, the surface remains superhydrophobic. Especially in underwater applications, the longevity of a superhydrophobic surface-how long the surface could maintain the entrapped air-is critical [8,9,11,20]. Recent overviews of the phenomenon are available [12,13,21].…”

A noise-resistant ADSA-PH algorithm for superhydrophobic surface’s static contact angle evaluation

“…Hydrophobicity is the key property of the superhydrophobic surface which is generally characterized by the static contact angle. [8][9][10][11][12] However, accurate evaluation of static contact angle for superhydrophobic surface is not trivial. [8][9][10][11] Even for the images with similar drop shape, the differences in the evaluated static contact angle by different researchers may be up to dozens of degrees.…”