Investigation of the time-dependent friction behavior of polyacrylamide hydrogels

Hydrogels have attracted enormous frictional investigation owing to their great potential in hydration lubrication. Researchers have revealed that the lubrication behavior of hydrogel depends on a number of parameters such as contact area, sliding velocity, and solution condition. However, less effort has been devoted to understanding the time-dependent friction behavior of polymeric hydrogels. In this work, the time-dependent behavior of hydrogel friction was systematically investigated through three typical polyacrylamide hydrogels (PAM, PAMPEI, and PAM-PAA) on a rheometer. Interestingly, the friction coefficients (mu) of the hydrogels varied with time, and two distinct regimes (viz., the friction-decrease regime and friction-constant/increase regime) were