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种类的机械部件中实现滑动表面上的低摩擦。众所周知，润滑剂可在表面附近形成一些吸收层。虽然润滑剂（或吸收层）与摩擦学性能之间的宏观关系已被广泛研究，但在固液界面处形成的特殊吸收层的密度和厚度还未见报道，本实验室用中子反射法直接测量了固体表面附近润滑剂的密度，并在一系列研究中进行了讨论。由于中子不是与电子发生物理作用，而是与原子核发生物理作用，因此中子可以深入到普通金属的内部区域，便于实现固液界面的原位观测。反射计通常用于通过反射率分布分析样品或界面的垂直微观结构。本文研究了三种DLC 关于我们 制备具有不同表面能的膜作为基础材料，并选择水作为润滑剂。DLC膜被称为“正常DLC”，“亲水DLC”和“疏水DLC”，第一个是通过等离子体CVD使用CH_4气体沉积在硅块上，第二个是通过氧气等离子体处理作为后处理在正常DLC的表面上，第三个是通过等离子体CVD使用CH_4和C_2F_6沉积的。将DLC膜浸泡在特制的样品保持器中，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）的中子反射仪“MINE”，并从DLC膜和水之间的界面处的中子反射率分布的仪器获得。通过Parratt理论对所获得的轮廓的分析拟合方法，我们可以看到：（1）亲水层厚度（2）水从亲水性类金刚石表面渗入到内部，直至15 nm，亲水类金刚石膜表面渗透的致密水层厚度约为2nm;疏水类金刚石膜表面渗透的低密度水层厚度约为3 nm，其密度约为正常水的一半。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