of proteoglycans and collagen fibrils with high water content (75-80 wt%) has attracted the lubrication with gel materials possessing high mechanical strength [4][5][6][7] and stable low friction. [8][9][10][11][12] These researches aim at shedding light on the gel properties and their potential application as artificial biomaterials.However, such advantages can hardly be realized for industrial uses since solvent (ex. water) in the gels can easily evaporate to lose swelled state. For this purpose, we focused on ionic liquids (ILs) to retain their swelled state. ILs are liquid salts fully composed of cations and anions, generally so-called when their melting temperature is lower than 100 °C. [13] Their high thermal/oxidative stability, negligible volatility, low frictional properties, and facile tenability of these physicochemical properties by their molecular design, [14][15][16] which are the desired characteristics of swelling agents of low frictional gels. In addition, demand for immobilizing ILs on solid surface with keeping their physicochemical properties to fabricate functional devices [17] have opened up the development of gel materials incorporating ILs, so-called as "ion gels" or "ionogels." [18] Ion gels can roughly be classified to physical or chemical gels. [18] In case of physical gels, cross-linking point of their polymer network is formed with relatively weak interaction like hydrophobic interaction, hydrogen bond, π−π interaction and so on, while chemical gels are cross-linked with covalently bonds. There have been several reports studying on tribological behavior of physical ion gels dispersed in ILs. [19][20][21] Espejo et al. characterized the tribological properties of a bucky gel with multiwalled carbon nanotube and 1-ethyl 3-methylimidazolium tosylate. [20] These combination at a tribopair of AISI 316L stainless steel and polycarbonate under 0.98 N at 0.1 m s −1 resulted in COF of 0.025, which is lower than that of a neat IL. In contrast, study on tribological properties of chemical ion gels with sheet-like morphology has not been reported in spite of their high mechanical strength and ease for immobilizing on solid devices.We have recently reported a lubrication system based on ILs and compatible polymer brushes grafted on a Si substrate showed efficient and robust lubrication. [22] They were composed of an ionic liquid, N, N-diethyl-N-(2-methoxyethyl)-N-methylammonium bis(trifluoromethylsulfonyl)imide (DEME-TFSI), and high density ionic liquid polymer brushes composed of the derivative of DEME-TFSI with a polymerizable group, Reducing friction is important to improve the lifetime and energy efficiency of mechanical systems. Since human joints with gel-like structure possess a coefficient of friction as low as 10 -3 , gel materials are recognized as a useful example for designing low frictional materials. Ion gels incorporating ionic liquids (ILs) as swelling agent is expected to be stable gel lubricant since high thermal stability and negligible volatility of ILs can maintain swelled sta...
