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Tribological Properties of Double-Network Gels Substituted by Ionic Liquids

Department of Creative Engineering, National Institute of Technology, Tsuruoka College, 104 Sawada, Inooka, Tsuruoka 997-8511, Japan
Author to whom correspondence should be addressed.
Lubricants 2018, 6(4), 89;
Received: 9 September 2018 / Revised: 1 October 2018 / Accepted: 6 October 2018 / Published: 8 October 2018
(This article belongs to the Special Issue Ionic Liquids: Friction and Lubrication Mechanisms)
Since human body joints have a gel-like structure with low friction that persists for several decades, hydrogels have attracted much interest for developing low-friction materials. However, such advantages can hardly be realized in industrial usage because water in the gel evaporates easily and the gel deswells. The substitution of water with an ionic liquid (IL) is one of the effective ways to overcome this problem. In this study, we substituted water in a double network (DN) hydrogel with 3-ethyl-1-methyl-imidazolium ethylsulfate (EMI-EtSulf), a hydrophilic IL, via a simple solvent exchange method to obtain a DN ion gel. A compressive test and thermogravimetric analysis showed that the DN ion gel has a high compression fracture stress and improved thermal properties, with the difference in 10% loss of temperature being ΔT10 = 234 °C. A friction test conducted using a reciprocating tribometer showed that the friction of a glass ball/DN ion gel was relatively higher than that of a glass ball/DN hydrogel. Because the minimum coefficient of friction (COF) value increased after substitution, the increase in polymer adhesion caused by the electrostatic shielding of the surface moieties of glass and poly 2-acrylamidomethylpropanesulfonic acid (PAMPS) was considered the main contributor to the high friction. As the COF value decreased with increasing temperature, the DN ion gel can achieve low friction via the restriction of polymer adhesion at high temperatures, which is difficult in the DN hydrogel owing to drying. View Full-Text
Keywords: double-network gel; ionic liquid; electrostatic interaction; low friction double-network gel; ionic liquid; electrostatic interaction; low friction
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Arafune, H.; Muto, F.; Kamijo, T.; Honma, S.; Morinaga, T.; Sato, T. Tribological Properties of Double-Network Gels Substituted by Ionic Liquids. Lubricants 2018, 6, 89.

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