Drawing of microshear deformation zones in glassy polymers: Poly(phenylene oxide) (PPO)

Abstract

The topography of the microscopic shear deformation zones (SDZ) in the glassy polymer PPO was studied by using atomic force microscopy (AFM) and was used to analyze the growth and breakdown of the SDZ. It was found that the local stress and strain are almost constant within the deformation zones but higher than those in the elastic regions. The maximum strain rate during stretching was found to always locate near the SDZ boundaries, indicating that most drawing took place there. With both the local stress and strain obtained for every point within the SDZ, it is possible to construct a full stress-strain curve for the drawing of the tiny local deformation zones. The stress-strain curve clearly demonstrates a yield point in the beginning of microyielding where the tensile modulus was found to be much lower than that in the elastic regime. Some strain hardening, however, took place at larger deformation. Moreover, we found that for each microscopic region participated in the microdrawing the local strain rate increased with local strain until a critical strain around 0.65 was reached, after which the strain rate decreased with strain. This critical strain may be related to the chain entanglement network structure because it shifted to 0.75 when PS diluents were blended into PPO, indicating that strain hardening was delayed by the increase of chain entanglement mesh size. (C) 1996 John Wiley & Sons, Inc.