Role of water in the lubrication of hydrogel

In previous reports, the frictional property of hydrogel was evaluated by using the pin-on-disk type of friction tester. As a result, the hydrogel showed the change in a friction coefficient depending on the speed. The friction property of hydrogel is similar to the Stribeck curve. From this result, it was confirmed that the hydrogel was operated by the mode of hydrodynamic lubrication.In order to investigate the effect of mechanical property and chemical characteristic of hydrogel for hydrodynamic lubrication, the hydrogel was prepared by using two kinds of monomers and by changing the gel concentration. The frictional property of hydrogel was evaluated by using the pin-on-disk type of friction tester.The friction coefficient does not depend on the hardness. It depends on the speed. The friction properties of hydrogel at the speed/load showed the Stribeck curve. It was confirmed that the hydrogel showed the behavior of the hydrodynamic lubrication at low load and high velocity. Although the hardness of both hydrogels is the same, the Stribeck curve of the DMAA hydrogel showed the friction coefficient which was lower than that of the AAm hydrogel. NOE spectrum of both hydrogels with the lowest friction and with the same hardness was measured in NMR. With the comparison of the NOE phenomenon of two hydrogels, DMAA hydrogel showed NOE phenomenon, which was clearer than AAm hydrogel. It was indicated that the low friction was caused by the attractive force of the water molecule in the hydrophilic macromolecule chain. It is important to realize that the low friction of hydrogel is caused by the hydrophilic macromolecule chain attracting the water molecule.