The Frictional Behavior Of Poly(2-acrylamido-2-methylpropanesulfonic Acid) Hydrogel Sliding Against Glass Surface

The PAMPS gel was prepared by radical polymerization and the friction of PAMPS hydrogel sliding against glass in water and PAAS aqueous solution was measured. The influence of sliding velocity(v), compressive modulus(E) of hydrogel, the thickness of hydrogel(h) and the concentration of PAAS solution on the frictional behavior of hydrogel were investigated. The repulsion-adsorption model, scaling theory and other related theorys was used to analayze the experimental results.It reveals that the frictional stress (f) increases with increase sliding velocity ( v ) at high velocity region, and f∝v~1 prevails, which is considered as the hydrodynamic lubrication. However, at small v region, f∝v~1 failed and f decreases slightly as v increase. The decrease of f with v in small v region is believed to arise from the shearing thinning of PAMPS hydrogel surface network and the decrease of shearing area. PAMPS gel with E exhibits high f than that of hydrogel with small E at slow v region, this is believed to be related to lower viscosity of hydrogel blobs on the surface of hydrogel with small E and mixed lubrication. Additionally, the critical velocity v_c increases with increase in the modulus of hydrogel, this may arise from large deformation of hydrogel with small E.For the friction of PAMPS hydrogel in PAAS aqueous solution at slow v region f decreases with the increase of sliding velocity, this is believed to be related to shearing mining of PAAS chain and mixed lubrication. At high velocity region f increases with increase of v and the frictional mechanism is considered as the hydrodynamic lubrication. When the concentration increases to 300C*, the f increase monotonously with v, this may be due to a complete PAAS solution layer has formed between PAMPS gel and glass and there is no direct contact between hydrogel and glass. At slow v region, f decreases with the increase in the concentration of PAAS aqueous solution, this may arise that the concentrated PAAS solution prevents the direct contact between PAMPS hydrogel and glass substrate.