Studies of drag on the nanocomposite superhydrophobic surfaces

The nanocomposite thin films of stearic acid (SA)-functionalized ZnO nanoparticles incorporated in epoxy polymer matrix have been achieved. The X-ray diffraction (XRD) studies show the formation of zinc stearate on ZnO nanoparticles as the confirmation of SA-functionalization of ZnO nanoparticles in the thin films. Morphological analyses reveal the presence of micro-holes with the presence of irregular nanoparticles. The measured root mean square (rms) roughness of the thin film is found to be 12 +/- 1 mu m with the adhesion of 5B on both glass and aluminum substrates. The wetting property shows that the surface of the film is superhydrophobic with the contact angle of water of 156 +/- 4 degrees having contact angle hysteresis (CAH) of 4 +/- 2 degrees. The average terminal velocity in the water of the as-received glass spheres and superhydrophobic spheres were found to be 0.66 +/- 0.01 m/s and 0.72 +/- 0.01 m/s respectively. Consequently, the calculated average coefficients of the surface drag of the as-received glass sphere and superhydrophobic glass sphere were 2.30 +/- 0.01 and 1.93 +/- 0.03, respectively. Hence, the drag reduction on the surface of superhydrophobic glass sphere is found to be approximately 16% lower than as-received glass sphere. (C) 2014 Elsevier B.V. All rights reserved.