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The dynamic wetting and dewetting of a water droplet on a hydrophobic solid surface with an equilibrium contact angle of approximately 100° was investigated using molecular kinetic (MK) theory to model the extension–contraction experiment and numerically calculate the radius of the contact line circle between the solid and liquid, contact line velocity, and dynamic contact angle. Furthermore, the numerical calculation results were examined in terms of various coefficients of the contact line friction to evaluate the mobility of the contact line. The calculation results of wetting and dewetting were in quantitative agreement with our previous experimental results, indicating that our constructed model was appropriate. Therefore, the MK theory can be applied to explain the characteristics of dynamic wetting and dewetting of droplets on hydrophobic surfaces, as with hydrophilic surfaces.

Recently, there has been a growing interest in utilizing surface texture to enhance the tribological properties of sliding components. Particularly noteworthy is the application of tool vibration at ultrasonic frequencies for efficiently generating surface textures. This study focuses on generating surface texture on the end surface of a stainless steel disk through ultrasonic assisted turning. The mathematical expression of the theoretical texture configuration, derived from the tool trajectory, is closely aligned with the actual machined surface. A novel geometric analysis was conducted to address the challenge of interference between the finished surface and the flank surface, resulting in a reduction in texture height. This analysis revealed that the texture height error from the theoretical value was limited to within 10%. Ball-on-disk tribological experiments were also performed on the textured surface to assess starting friction phenomena. The findings indicated that surfaces with texture exhibited a more minor fluctuation in the starting friction coefficient compared to those without texture. In summary, this paper explores the efficient generation of surface texture on stainless steel disks using ultrasonic assisted turning. Theoretical configurations were mathematically expressed and aligned well with actual machined surfaces. The study also introduced a novel geometric analysis to address interference-related texture height reduction. Moreover, tribological experiments demonstrated that textured surfaces experienced a more stable starting friction coefficient, highlighting the potential of surface texturing for improving tribological properties in sliding components.

Inspired by the water-repellent and self-cleaning properties of the lotus leaf in the natural world, artificial superhydrophobic surfaces have attracted extensive interest in academia and industry. Static and dynamic hydrophobicities are very important phenomena in our daily life as well as in many industrial processes. However, the difference between these two phenomena has not been well understood. The objective of this study was to investigate and predict the sliding behavior of water droplets on silicone sheet surfaces with uniaxial groove structures. The groove structures were fabricated on silicone sheet surfaces by a molding process using three different molds with different groove widths. Increasing the groove width decreased the sliding angle. The sliding angle could be reduced to a greater extent than that of previously reported fluorinated hydrophobic surfaces, which exhibited sliding angles of less than 2°. The retention force between the water droplet and the silicone sheet surface was proportional to the contact ratio. It was found that the retention force was proportional to the shape of the water droplet on the surface at the sliding angle, especially the product of the contact angle hysteresis and the width of the contact line. [ABSTRACT FROM AUTHOR]