TRIBOLOGICAL DESIGN FOR MICRO SLIDING BEARINGS

在微系统的可移动部件中，由表面力引起的摩擦磨损增加是最严重的问题之一，因为在微尺寸系统中，表面力相对于体积力占主导地位。在这项研究中，基于一种新的利用表面张力的润滑原理开发了一种滑动轴承，这种原理在微细系统中是有利的。轴承的两个运动表面覆盖有疏水薄膜，水滴被限制在它们之间。该轴承通过水滴与疏水薄膜之间产生的排斥力来支撑法向载荷，并由于水滴在疏水薄膜上的低流动阻力而表现出很低的摩擦力。结果表明，表面越粗糙，摩擦越小，承载能力越高。结果表明，在低剪切速度下，产生摩擦力的主要因素是水滴变形引起的动态表面张力，粘性力的一个分量随着剪切速度的增加而逐渐增大。在低剪切速度下，摩擦系数小于0.001，水滴以1.5m/s的速度滑动。此外，还利用光刻和刻蚀技术创建了疏水表面的微图形，并形成了自组装单层。在用这种方法获得的各种表面上，测量了水滴的滑动角和剪切力。结果表明，表面粗糙度大到足以将空气夹在水滴和疏水表面之间时，表面有凹陷的表面表现出较小的摩擦力，剪切力显著降低。

In movable parts of microsystems, increase in friction and wear caused by surface forces is one of the most serious issues, because the surface forces become dominant compared with volume forces in microsized systems. In this research, a sliding bearing on the basis of a new lubrication principle utilizing surface tension, which is advantageous in microsized systems, has been developed. Two moving surfaces of the bearing are coated with hydrophobic films and water droplets are confined between them. The bearing supports normal load by the repulsive force generated between the water drops and the hydrophobic films, and exhibits very low friction because of the low flow resistance of the water drops on the hydrophobic filmsLoad carrying capacity and flow resistance of a water droplet on two fluoride films with different roughness have been measured. The results show that the rougher surface exhibits lower friction and higher load carrying capacity. It is found that the major factor contributing to the friction force at low shearing velocity is dynamic surface tension caused by deformation of the water droplet and a component of viscous force increases gradually as shearing velocity increases. The coefficient of friction is less than 0.001 at low shearing velocity and the water droplet operates as a bearing at sliding velocities up to 1.5 m/s.Additionally, creation of micropatterned hydrophobic surfaces using photolithography and etching techniques and SAM (Self Assembled Monlayer) formation has been carried out. On various surfaces obtained by this method, sliding angles and shearing forces of a water droplet have been measured. It is found that the surfaces with bumps exhibit lower friction than those with dents, and that shearing force decreases significantly when the surface roughness is high enough to trap air between the water droplet and the hydrophobic surface.