Effect of double network hydrogel film thickness on the run-in tribological properties of a friction system using DN gel

This study aims to investigate the potential of double network hydrogel (DN gel) in a low friction mechanical system. In this study, the effect of the thickness of DN gel films on the friction property are clarified. An indentation test, contact pressure measurement, and series of friction tests in water using three different thickness (1.5, 3, 6 mm) of DN gel film and a SiC disc were carried out. Friction of DN gel film sliding against SiC in water can be classified into two types as “Friction region I: friction remains substantially unchanged during the test” and “Friction region II: friction decreases due to run-in”. Friction region transition can be related to the Hersey number region, which consists of viscosity of lubricant, sliding speed and apparent contact pressure. Hersey number larger than 1.5 × 10−10 is a necessary condition for friction region II where different lubrication regimes can be found. 1.5 and 6 mm thick DN gel films have exhibit super low friction (μ