Ionic liquids (ILs) are organic salts consisting of anions and cations that exist as liquids at room temperature. ILs exhibit many attractive properties such as negligible volatility, low flammability, and relatively high thermal stability. These properties can be varied in a controlled fashion through systematic changes in the molecular structure of their constituent ions. Some recent studies have aimed to use ILs as new lubricant materials. However, the behavior of ILs as lubricants on the sliding interfaces has not been elucidated. In this chapter, we describe the nano- and macrolubrication properties of some ILs with different types of anions using resonance shear measurement (RSM) and conventional ball-on-plate-type tribotests, respectively. This study reveals that the properties observed by RSM for nanoscale systems can provide important insights for the study of the friction coefficients (macrolubrication properties) obtained by tribotests.
Part of the book: Ionic Liquids
Friction reduction is imperative for improving the service life and energy efficiency of mechanical systems. Ion gels using ionic liquids (ILs) as swelling agents are expected to be stable gel lubricants owing to the high thermal stability and negligible volatility of ILs; they can maintain their swollen state even under harsh conditions. Therefore, we investigated two types of ion gels: an IL-substituted double-network gel (DN ion S-gel), in which the water in the DN hydrogel is replaced by the IL 3-ethyl-1-methyl-imidazolium ethylsulfate; and a DN ion gel containing N,N-diethyl-N-(2-methoxyethyl)-N-methyl-ammonium bis(trifluoromethylsulfonyl)imide (DEME-TFSI), where one of the polymer backbones is a network of poly(N,N-diethyl-N-(2-methacryloylethyl)-N-methylammonium bis(trifluoromethylsulfonyl)imide), an IL-type polymer based on our previous synthetic study of IL polymer technology. The DN ion S-gel and DN ion gel achieved compression strengths of 25 and 30 MPa, respectively, and were thermally stable until 196°C and 335°C (10% weight-loss temperature), respectively. The coefficient of friction remained stable and low (0.02) after repeated measurements under harsh conditions (high temperature or vacuum conditions), affirming the durability of the DN ion gel.
Part of the book: Industrial Applications of Ionic Liquids