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

润滑剂通常有助于在许多机械部件的滑动表面上实现低摩擦。众所周知，润滑剂可以在表面附近形成一些吸收层。虽然人们已经研究了润滑剂（或吸收层）与摩擦学性能之间的宏观关系，但关于在固液界面形成的特殊超薄层的密度和厚度的报道还没有。在我们的实验室里，用中子反射法直接测量了固体表面附近润滑剂的密度，并在一系列的研究中进行了讨论。由于中子与原子核的物理作用不是与电子的物理作用，因此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。反射率法通常用于通过反射率曲线分析样品或界面的垂直微观结构。本文制备了三种具有不同表面能的DLC…More薄膜作为基材，并选择水作为润滑剂。DLC膜被称为“正常DLC”、“亲水性DLC”和“疏水性DLC”；第一个是用CH4气体等离子体气相沉积在硅块上，第二个是用氧气等离子体在普通DLC表面进行后处理，第三个是用CH4和C_2F_6等离子体气相沉积。将DLC膜浸泡在特殊设计的样品支架中，中子束从硅块侧面直接进入DLC/水界面。然后，我们使用的仪器是日本原子能机构（JAEA）的中子反射率计“MINE”，通过该仪器获得了DLC膜与水界面的中子反射率曲线。利用Parratt理论对得到的剖面进行解析拟合，可以看出：(1)在亲水DLC表面形成的亲水层（O_2等离子体处理层）厚度为15nm；(2)水从亲水DLC表面向内部渗透至15nm深度，在亲水DLC上表面渗透的致密水层厚度为2nm；(3)疏水DLC表面的低密度水层厚度为3nm，其密度几乎是正常水的一半。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