Static contact angle (gray full circles) and contact angle hysteresis (black full circles) vs the etching time . The insets show the photographs of water drops with a radius of on flat and water repellent surfaces.
AFM micrographs [top (a) and three-dimensional view (b)] and surface profile (c) of silanized film preirradiated with and then etched for . The parameters and corresponding respectively to the average distance between two holes and to the thickness of the wall between these structures are also indicated in the figure.
Static contact angle as a function of the surface aspect ratio . The dashed lines are drawn only to guide the eye.
Surface roughness power spectra for silanized film (a) and for two samples etched for (gray) and (black), respectively (b). is the Hurst exponent related to the fractal dimension by .
Height distribution for silanized film (a) and for two samples etched for (b) and (c), respectively. The parameters and correspond respectively to the average height and to the straggling extracted from the Gaussian distributions used to fit the experimental curves. The height distributions were measured on a scanned zone of .
Cosine of the measured contact angle as a function of both and .
Etching time , experimental hole diameter , calculated depth of hole structures , measured static , advancing and receding contact angles, lineic fraction of the solid surface in contact with the liquid determined from AFM images, and Wenzel contact angle . The measured contact angles are given with an accuracy of 3°.
Etching time , fractal dimension determined by the PSD method, upper and lower limit lengths of the fractal structure, fractal roughness value , rms-roughness value measured on a scanned zone of , and threshold static contact angle determined from Eq. (4).
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