REVERSAL AND ACTIVATION OF PHYSICAL AGING BY APPLIED DEFORMATIONS IN SIMPLE COMPRESSION AND EXTENSION

The differential (incremental) storage modulus E prime was measured intermittently at 1 Hz during the stress relaxation of cylindrical specimens of polycarbonate subjected to finite static strains in both simple compression and extension. (In measuring E prime , the amplitude of the applied sinusoidal strain was 0. 2%). Application of each static strain gave a value of E prime /E prime // less than unity, where E prime //0 prime is the storage modulus at 1 Hz of the undeformed specimen. This behavior results from an increase in the mobility of short molecular segments; it signifies a partial erasure of the state of physical aging, a change also termed de-aging or rejuvenation. After a static strain had been applied, E prime increased continuously, a reflection of physical aging that results from a progressive decrease in segmental mobility. Plots of E prime /40 // at an aging time of 100 s against the absolute value of the static strain show that simple extension de-ages a specimen somewhat more than does a strain of the same magnitude in compression.