Effect of Surface Energies of DLC Films to Ito Tribological Properties under Lubricated Condition

在许多类型的机械部件中，润滑剂通常有助于在滑动表面上实现低摩擦。众所周知，润滑剂可能会在表面附近形成一些吸收层。虽然润滑剂(或吸附层)与摩擦学性能之间的宏观关系已被广泛研究，但在固液界面形成的特殊超薄层的密度和厚度尚未见报道。在本实验室，润滑剂在固体表面附近的密度是用中子反射仪直接测量的，并在系列研究中进行了讨论。由于中子物理上不是与电子相互作用而是与原子核相互作用，所以中子可以深入到普通金属的内部区域，从而很容易实现对固液界面的原位观测。反射仪通常用于通过反射率分布分析样品或界面的垂直微结构。在本文中，三种类型的类金刚石…制备了更多不同表面能的薄膜作为基材，选择水作为润滑剂。DLC膜被称为“正常类金刚石膜”、“亲水性类金刚石膜”和“疏水性类金刚石膜”，第一类类金刚石膜是在硅胶块上用CH4气体等离子体CVD沉积的，第二类膜是用氧气等离子体在普通类金刚石膜表面进行后处理处理的，第三类类金刚石膜是用CH4和C2F6作为后处理气体的等离子体CVD沉积的。然后，我们使用的仪器是日本原子能机构(JAEA)的中子反射仪MINE，利用该仪器获得了类金刚石薄膜与水界面的中子反射率分布。通过用Parratt理论对得到的分布进行解析拟合，可以看出：(1)亲水性DLC表面形成的亲水层(O2等离子体处理层)的厚度为15 nm，(2)水从亲水DLC表面向内部渗透到15 nm深，渗入到DLC顶面的致密水层厚度为2 nm，(3)疏水DLC表面的低密度水层厚度为3 nm，其密度几乎是正常水的一半。较少

Lubricants generally contribute to achieve low friction on sliding surfaces in many kinds of mechanical components. It is well known that lubricants may form some absorption layers near surfaces. Though macroscopic relationships between lubricants (or absorption layers) and tribological properties have been studied everywhere, there are no reports on densities and thicknesses of the special ultrathin layers formed at the solid-liquid interface.In our laboratory, densities of lubricants near solid surfaces are directly measured by neutron reflectometry and discussed in the series of studies. The neutron can go deeply into the inner region of common metals because neutrons physically interact not with electrons but with atomic nuclei, thus the in-situ observations of solid-liquid interface can be easily realized. The reflectometry is generally utilized for analysis of vertical microstructures of a sample or the interface through the reflectivity profile. In this paper, three kinds of DLC … More films having different surface energies were prepared as base materials, and water was selected as a lubricant. The DLC films were called 'normal DLC', 'hydrophilic DLC' and 'hydrophobic DLC'; the first was deposited by plasma CVD using CH4 gas on a silicone block, the second was treated by oxygen gas plasma on the surface of the normal DLC as post-processing treatment, and the third was deposited by plasma CVD using CH_4 and C_2F_6. The DLC films were soaked in water in a specially-designed sample holder, and the neutron beam was directly entered to the DLC/water interface from the side of silicone block. Then, the instrument we used was a neutron reflectometer 'MINE' in Japan Atomic Energy Agency (JAEA), and the neutron reflectivity profiles from the interface between DLC films and water were obtained by the instrument. Through an analytical fitting approach with Parratt's theory to the obtained profiles, we can see that: (1) the thickness of hydrophilic layer (O_2 plasma treated layer) formed in the surface of hydrophilic DLC is 15nm, (2) water is infiltrated from the surface to the interior of hydrophilic DLC until 15 nm-depth, and the thickness of dense water layer infiltrated in the top surface of hydrophilic DLC is 2nm, and (3) the thickness of low-density water layer on the surface of hydrophobic DLC is 3nm, and its density is almost half of normal water. Less