【作者】 刘思思；

【导师】 张朝辉；

【作者基本信息】 北京交通大学 ， 机械设计及理论， 2014， 博士

【摘要】 在微机械领域,尺度效应的存在使得材料表／界面特性成为决定微器件功能的关键因素。在微／纳米尺度上,相互接触或存在微间隙的表面间黏着效应显著,从而导致微观表面受到严重黏着磨损而失效。对材料表面进行加工和改性使其具有超疏水性能是改善固体表面力学性能和摩擦学性能的有效方式,在微／纳机电系统领域有重要的学术和工程价值。本文建立亲水表面微观粗糙结构模型,基于Gibbs自由能法则,并考虑接触角滞后能的前提下,利用该模型从能量角度揭示了表面形貌对固体表面润湿性能的影响规律,归纳得到了液滴在亲水性粗糙表面稳定处于Cassie状态时,微观粗糙结构形貌特征、几何参数、分布特性的设计准则。通过建立微／纳米尺度上平面-平面,球面-平面以及球面-球面间弯月面模型,基于Young-Laplace方程和Reynolds润滑理论,分析得到固体表面接触分离过程中弯月面力和黏着力的计算公式。在此基础上,计算得到接触表面分离过程中的弯月面形状变化规律,并分别讨论了固体表面分离距离、液滴初始弯月面高度、固体表面润湿性能、分离时间、断裂高度等因素对弯月面力和黏着力的影响。研究结果为微／纳米表面抗黏着机理提供了理论依据。采用电感耦合等离子体刻蚀法,在单晶硅基底上加工微米级方柱阵列粗糙结构并修饰十八烷基三氯硅烷(octadecyltrichlorosilane, OTS)自组装分子膜,成功获得了性能稳定的超疏水表面。通过接触角与接触角滞后的测量,进一步分析表面微观粗糙结构特征参数以及自组装分子膜特性对表面润湿性能的影响规律。讨论了液滴在亲水性方柱阵列表面发生润湿状态转变的原因,得到了与理论预测一致性较好的实验结果。基于表／界面科学理论和摩擦学原理,分析超疏水表面减摩、抗磨、抗黏着机理,综合探讨微观和宏观摩擦学性能,总结和归纳出微观粗糙结构和OTS自组装分子膜对减小摩擦并延长自组装分子膜寿命的协同效应,得到了OTS自组装分子膜在干摩擦条件下具有良好的减摩、抗磨性能的结论。更多还原

【Abstract】 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.更多还原