Interfacial Structure and Nanotribological Property of Adsorption Layer Formed by Polyacrylate Type Friction Modifiers Having Poorly-Oil-Soluble Units

 

Naohiro Kikuchi, Tomoko Hirayama, Hidetoshi Sakamoto, Takashi Matsuoka

（Doshisha University），

Ko Onodera, Honami Watanabe, Takehisa Sato (EMG Lubricants Godo Kaisya)

Abstract

The adsorption layer formed onto the metal surface by polyacrylate type friction modifier having poorly-oil-soluble units (ArAC) was investigated using multiple interfacial analysis methods. This friction modifier is copolymer prepared by polymerizing polar units, oil-soluble units, and poorly-oil-soluble units at a certain ratio. For the in-situ analysis of the layer, attenuated total reflection infrared spectroscopy (ATR-IR) specialized for surface analysis among Fourier transform infrared spectroscopy (FT-IR), neutron reflectometry (NR) superior in depth direction analysis to the interfacial structure, and atomic force microscope (AFM) which can analyze the surface morphology and friction property of the adsorption layer in the order of nm were used as interfacial analysis methods. We used copper as the target substrate, hexadecane added with ArAC 0.1 mass% was used as the lubricating oil model in this study. As a result of these analyses, it was revealed that ArAC formed an adsorption layer having a thickness of 25 nm immediately after contacting the metal surface with ArAC added oil, increasing its film thickness and density with time. It was also found that the layer does not peel off even after sliding at 210 MPa for 1 hour, and continuously exhibits the friction reduction effect. On the other hand, film thickness increased and the density decreased under high temperature conditions. From this, it is presumed that the adsorption layer swells under high temperature conditions and exhibits further friction reduction effect.