Characterization of irregularly micro-structured surfaces related to their wetting properties

Abstract It is difficult to control a surface wetting due to the random surface texture, but its fabrication is easy. Hence, the volume ratio is proposed through the 3D characterization of micro-structured surface in contrast to traditional roughness factor, fractal dimension and aspect ratio through 2D characterization. The objective is to investigate the wetting properties related to the characterization of irregularly micro-structured surface. First, the irregularly micro-structured Si surfaces with 0.22–3.58 μm in depth were machined by the rubbing, the polishing and the grinding with different diamond abrasive grain size and random abrasive grain shape, respectively; secondly, the surface wetting properties were investigated with regard to the characterized parameters of measured micro-topographic surfaces; finally, the irregular wetting model was constructed by using volume ratio on the base of non-composite wetting. It is shown that the contact angle increases with increasing roughness factor and aspect ratio and decreasing fractal dimension on the irregularly micro-structured surfaces, but it is different from the prediction of non-composite wetting model. Moreover, the irregularly micro-structured surfaces without anisotropic properties produce smaller contact angles than regularly micro-structured surfaces with anisotropic properties. The experimental results show that an increase in volume ratio leads to a decrease in contact angle. It is identical to the predictions of the proposed model. This is because the volume ratio precisely illustrates 3D contact information between the liquid and solid interfaces. It is confirmed that the volume ratio may be utilized to predict and control the wetting of irregularly micro-structured surface.