Wettability And Tribology Properties Of Microscale Silicon-based Superhydrophobic Surface

In the micro mechanical field, scale effect makes the material surface/interface properties become key factors to the micro device functions. In micro/nanoscale, there is a significant adhesion between contact or near-contact surfaces, which leads to a severe adhesion, wear and failure at last. It is an effective way to improve the mechanical and tribological properties of solid surfaces by making them superhydrophobic, and it is of considerable value academic and engineering value to micro/nano electromechanical systems.The microscale roughness model on hydrophilic surface was proposed. Based on the model, the effect of surface topography on solid surface wettability was revealed considering of Gibbs free energy and contact angle hysteresis energy. The design criterions of morphology, geometrical parameter and distribution characteristic of microscale rough structure were summarized under the state where the water droplet can stay in a stable Cassie wetting state.Meniscus models of medium droplet between micro/nanoscale contact or near-contact flat-on-flat, sphere-on-flat and sphere-on-sphere surfaces were put forward. Based on the Young-Laplace equation and Reynolds lubrication theory, the meniscus force and viscous force formulae were deduced. During the separation of the contact or near-contact surfaces, the variations of meniscus shapes were illustrated. The effects of separation distance, initial meniscus height, surface wettability, separating time and fracture height on meniscus and viscous force during the separation were analyzed. The results provide a theoretical basis for the micro/nanoscale surface anti-sticking mechanism.Silicon (Si) substrates decorated with regular microscale square pillar arrays were prepared by inductively coupled plasma, and then they were silanized by self-assembly octadecyltrichlorosilane film. The silanized textured substrates finally attained stable superhydrophobicity. The effects of microscale rough structure and self-assembled monolayer properties on surface wettability were analyzed by measurement of contact angle and contact angle hysteresis. Moreover, the reason of wetting state transition on textured Si surface with hydrophilic pillar arrays was discussed, and the experimental results are in good agreement with the theoretical prediction.Based on surface/interface scientific theory and tribology principles, the mechanism of antifriction, wear-resistant and adhesive reduction properties of superhydrophobic surfaces were analyzed. The microscale and macroscale tribological properties were discussed and the co-effect of micro-rough structure and OTS self-assembled monolayer on antifriction and lengthening the self-assembled monolayer lifetime were summarized. The good antifriction and wear-resistant properties of OTS self-assembled monolayer under dry friction were found in the experiments.