The deformation of sliding objects plays an important role for determining the characteristics of frictional vibration. Therefore, to understand the frictional vibration of elastomers comprehensively, in-situ observations of contact area are necessary along with force measurements. In this article, after explaining the basics of frictional vibration using a single-degree-of-freedom model, some optical methods of visualizing the contact area (i.e., methods using transmission or reflection of visible light) are introduced. In particular, methods using the total reflection are hopeful to realize sensitive observations of contact area under dry or wet conditions.

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In this paper, we report our studies on sliding friction of soft and sticky polymer gels. When the gel is slid against a rigid substrate, formation of pulse-like detachment waves is observed, and the dynamical patterns of the detachment waves drastically change with the sliding velocity. Through simple visualization techniques to observe the stick-slip motions occurring at the interface, we succeed in characterizing the sliding behavior. We discuss the importance of visualization and meso-scale description of the phenomena.

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Energy-Filtering TEM (EFTEM) was performed for the investigation of polymer interfaces. Polymer-polymer adhesion with various interfacial thicknesses formed between styrene-acrylonitrile random copolymer (SAN) and poly(methyl methacrylate) (PMMA) was studied by oxygen and nitrogen mapping and electron-energy-loss spectroscopy (EELS). Polymers brushes grafted on silica nanoparticles and organic dyes adsorbed on silica nanoparticles have been successfully characterized by high-resolution carbon mapping with contamination-free TEM.

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Discussing about frictional mechanism between two solids, it is very important to observe the contact states between the solids during friction. Concerning about friction of rubber, because rubber around contact surface should be deformed by friction, frictional force of rubber depends on not only area of contact but also deformation of rubber around contact surface. A lot of rubber products, for example tires, roller for paper handling and so on, are rubbed against rough surface, and usually they are opaque. Thus it is difficult to observe contact states during friction by visible ray. In this paper, we introduce studies on observation of contact states between rubber and mated surface using X-ray Imaging method. The frictional force shows a correlation with the contact area or the shear stress of the rubber. Consequently, it was summarized that the real time observation during friction using X-ray imaging is very effective to understand the mechanism of rubber friction.

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The cholesteric liquid crystal was adopted for the visualization of temperature distributions of viscous fluid about scraper blades. It was found that the scraper blades, which form a tail of scraped fluid from the horizontal wing on the rear part of the blade, bring faster uniform bulk temperature of viscous fluid by the visualization.
For each of three types of scraper blades, temperatures of the viscous bulk fluid were measured by 24 Cu-Co thermocouples in the Votator-type agitated vessel with the triple helical ribbon.
Heat transfer to the scraped vessel wall was investigated in very low mixing Reynolds number and it was confirmed that heat transfer coefficient was the most high value, for the scraper blade with the horizontal wing.

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