Determination of mechanical properties of nanometer-thick liquid lubricant films for thin film lubrication technology

为了建立纳米厚液体润滑膜的力学模型，我们的目标是同时测量薄膜剪切过程中的力学响应和接触面积。采用本研究提出的高灵敏度剪切力测量方法，即纤维摆动法（FWM）来检测结构的力学响应。在FWM中，我们使用球端光纤作为剪切探头。为了建立力学模型，我们必须从FWM测量得到的力学响应中确定薄膜的物理性质，如粘度和弹性。这需要精确测量探针尖端和润滑膜之间的接触面积。为此，我们将FWM装置集成到倒置显微镜上，从样品基板的背面观察接触面积。实验结果表明，差干涉对比显微术能够有效地降低背景噪声，并能有效地测量进流距离时的接触面积。从实验结果定量地得到了薄膜的粘度。

To establish mechanical model of nanometer-thick liquid lubricant films, we aimed to achieve simultaneous measurements of mechanical responses and contact areas during the shearing of the film.Highly sensitive shear force measurement method developed in our previous study, which we called the fiber wobbling method (FWM), was used to detect the mechanical r esponses. In the FWM, we used the ball-ended optical fiber as a shearing probe. To construct the mechanical model, we have to determine the physical properties of the films, such as viscosity and elasticity, from the mechanical responses obtained by the FWM measurements. This requires precise measurements of the contact area between the probe tip and lubricant film. For this purpose, we integrated the FWM setup on to the inverted microscope and observe the contact area from the backside of the sample substrate. We found that the differential interference contrast microscopy was effective to reduce the background noise and succeeded the measurement of contact area during the FWM measurements. From the experimental results we quantitatively obtained the thin film’ s viscosity.