Abstract: PVAhydrogels with different crystallinities obtained by varying freeze/thawed process cycles, as well as 2-hydroxyethyl methacrylate(HEMA) and 2-hydroxyethyl acrylate(HEA) hydrogels sheets crosslinked by polyethylene glycol dimethacrylate(PEGDMA-16) were prepared. The slide frictional properties of these hydrogels had been studied. It is found that the frictional behavior of these hydrogels do not obey Amonton's law due to the hydrodynamic lubrication mechanism caused by the squeezed water from the surface of hydrogels. When the loaDIncreased, more free water is squeezed out from the surface of hydrogels, thus the frictional coefficient is decreased. When the PVAhydrogels are exposed to air, the evaporation of the free water on the surface of hydrogels causes the increase in the frictional coefficient of PVAhydrogels. Additionally, with the increase of crystallinity of PVAhydrogels or crosslinking density of HEA, HEMAhydrogels, the network lattice of hydrogels becomes smaller, the water is difficult to squeeze out, resulting in the increase of the frictional coefficient.

Key words: Frictional coefficient, Lubrication, Freeze/thawed technique, Hydrogels, Crystallinity, Bonding water