Plastic deformation of glassy polymers : correlation between shear activation volume and entanglement density

The structural relaxation caused by plastic deformation of polymer glasses is not yet fully understood.In particular, the size scale of the plastic shear zones is currently unknown. In this work, theeffect of molecular entanglement density on the shear activation volume of glassy polymers wasstudied. The shear activation volumes of miscible polystyrene-poly(2,6-dimethyl-1,4-phenyleneoxide) (PS-PPO) blends at different PS-PPO ratios were determined experimentally by both planestrain and uniaxial compression at constant strain rates. We find that the same correlation betweenthe shear activation volume and the entanglement density holds for the blend as well as forvarious pure glassy polymers. Since the shear activation volume is closely related to the size of the plastic shear zones, this correlation suggests that the cooperativity of the elementary processes of plastic deformation in glassy polymers scales with the entanglement density.