Topographical length scales of hierarchical superhydrophobic surfaces

Abstract

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Roughness dependent wettability of sputtered copper thin films: The effect of the local surface slope

“…31,32 Indeed, dual scale roughness (micrometer and nanometer scale roughness known as hierarchical roughness) favors superhydrophobicity. [33][34][35][36] Furthermore, nanoscale random roughness has been shown theoretically to have a relationship to the statistical roughness parameters as the roughness exponent α (0 < α < 1), which characterizes the degree of roughness irregularity at short length scales ((ξ, with ξ being the lateral correlation length), and the long wavelength roughness ratio σ=ξ with σ being the rms roughness amplitude (assuming weak surface roughness σ=ξ ( 1). 37 Another numerical work showed the impact of the roughness exponent α and mean square surface slope in tuning surface hydrophobicity.…”

The Role of Roughness in Random Superhydrophobic Surfaces

“…The results indicate that higher values of profile height are not essential for superhydrophobicity and most superhydrophobic formulations showed lower overall height (on glass and PC) compared to the non-superhydrophobic ones. The Ra parameter expresses the relative departure of the profile in the vertical direction, but does not provide any information about the slope, shapes, and sizes of the asperities or about the frequency and regularity of their occurrence [46] . In order for a surface to show superhydrophobic characteristics, sharp structures having needle-like shapes with high aspect ratio and small spacing are needed to increase capillary pressure and trapped air [52].…”

“…The two parameters were calculated using two different software programs (XEI and Gwyddion) for the 20 µm scan size to study the asymmetry of pillar heights and peakedness or bluntness of the surfaces. For reference, the skewness and kurtosis for dry lotus leaves were also calculated and their values were 0 and 3 respectively [46]. The results are shown in Tables 6-8.…”

“…Previous work studied the correlation between superhydrophobicity and the PSDF of randomly rough surfaces and showed that superhydrophobic surfaces had a higher roughness power per unit frequency along the entire sampling length compared to nonsuperhydrophobic surfaces [45]. A surface containing both micro and nano roughness, will give a PSDF with higher roughness with small length scales (shorter than 500 nm) compared to a surface containing only micro or nano roughness [46]. Ice adhesion strength for superhydrophobic surfaces was found to be dependent primarily on the autocorrelation length [47].…”

A Facile in Situ and UV Printing Process for Bioinspired Self-Cleaning Surfaces

“…Texturization changed the hydrophilic HBP (WCA < 90°) into a hydrophobic surface (WCA > 90°) more efficiently than through a reduction of the surface energy with the addition of PFUA (WCA of 108°, see also [ 7 ]). The impact of tailored hierarchical structures at micron and nanometer scales on large WCA increases is indeed significant [ 47 ], unless the texturized material is hydrophilic, such as alumina [ 48 ]. In this latter case, the addition of a hydrophobic surface treatment is essential to achieve the requested WCA increase beyond 150°.…”