Preparation And Estimation Of Superhydrophobic CuO Surfaces And Research Of Water-Droplet Evaporation

Hierarchical CuO structures were prepared by surface oxidation on copper foils, and superhydrophobicity was shown on the surfaces which were oxidized over30minutes and modified by lauric acid with low surface energy. The X-ray diffraction pattern of the Cuo surfaces implies that the Cu substrate after treatment with the mixed aqueous solution was slowly transformed to CuO. Through analysising the SEM images of surfaces with different oxidation time, copper oxidation process can be divided into three stages, and CuO nano-flowers form at the3rd stage. Polarization curves of hydrophobic copper and super-hydrophobic CuO surface were obtained by the electrochemical workstation, and it is found that superhydrophobic CuO surface has a higher corrosion potential and lower corrosion current, meaning that superhydrophobic CuO surface is more resistant to corrosion than the CuO.Fractal theory was used to estimate the surfaces with the MATLAB program, and the results show that the surfaces have obvious fractal characteristics. The trend of box dimension along with time can also be divided into three stages. What’s more, multifractal spectrums of the surface were calculated, and the results show that the CuO surface structures tend to be homogeneous along with time. Finally, combining the changing trends of contact angle and fractal dimension, it is found that the surface hierarchy determines the superhydrophobicity and the superhydrophobicity can be improved by increasing fractal dimension. The reason is analysised from theory.Experiments of micron-size water droplet evaporation on superhydrophobic CuO surface, hydrophobic CuO surface and hydrophobic Cu surface were conducted. The evaporation process of water droplets on three kind of surfaces has a significant difference. Based on the assumption of ellipsoidal droplet and uniform concentration gradient, theoretical analyses for both constant contact radius (CCR) and constant contact angle (CCA) models were made and theoretical solutions were derived accordingly, especially a modified solution of contact area was presented for CCA model. Moreover, comparisons between the theoretical solutions and experimental data of contact angle in CCR and CCA stage demonstrated the validity of the theoretical solutions. Meanwhile, the superhydrophobic CuO surface and hydrophobic Cu surface were found to behave in accordance with the CCA and CCR model, respectively. Finallly, the reason for the differences of the droplet evaporation model was discussed. As the contact line is not mobile and tends to be pinned on hydrophobic Cu surface. when evaporation proceeds, it must be accompanied by a reduction in contact angle. When the contact line is not pinned on superhydrophobic CuO surface so that it moves quickly as evaporation proceeds and it must be accompanied by a reduction in contact radius.