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和磨损增加是最严重的问题之一，因为在微系统中，与体积力相比，表面力占主导地位。在这项研究中，基于一种新的润滑原理的滑动轴承利用表面张力，这是有利于微尺寸系统，已经开发。轴承的两个运动表面涂有疏水膜，水滴被限制在它们之间。轴承通过水滴与疏水膜之间产生的排斥力来支撑正常载荷，由于水滴在疏水膜上的流动阻力小，因此轴承的摩擦力很小。测量了水滴在两种不同粗糙度的氟膜上的承载能力和流动阻力。结果表明，粗糙的表面具有较低的摩擦和较高的承载能力。研究发现，低剪切速度下摩擦力的主要影响因素是水滴变形引起的动态表面张力，黏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，在高达1.5 m/s的滑动速度下，水滴起着轴承的作用。此外，利用光刻和蚀刻技术以及自组装单层膜（SAM）形成的微图案疏水表面已经进行了创建。在用这种方法得到的各种表面上，测量了水滴的滑动角和剪切力。结果表明，凹凸表面的摩擦力比凹凸表面的摩擦力小，当表面粗糙度足够高时，水滴与疏水表面之间的空气被截留，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.