ENERGY-CONSUMING MICROMECHANISMS IN THE FRACTURE OF GLASSY-POLYMERS .1. CHAIN SCISSION IN POLYSTYRENE

The number of chain scissions per unit area that occur during the fracture of partially annealed latex films from M(n) congruent-to 180,000 g/mol polystyrene particles of about 275 angstrom radius were measured and correlated to annealing times. A curve with four regimes was found. At short annealing times the curve is nearly flat, in what is called the chain pull-out regime. In the second regime, the number of chains broken per unit area increases with a 0.8 power of annealing time as entanglement of the diffusing polymer chains increases in neighboring host particles. This is in good agreement with Wool's theory which predicts a 0.75 power dependence. Then, after reaching a peak, the number of scissions decreases in the third regime, indicating a change in fracture mechanism. The number of chain scissions increases again in the fourth regime, as final healing of the film interface takes place. Fracture surface analysis reveals a rough surface for short annealing times and a smooth surface for longer annealing times. The number of polymer chain scissions per unit area of fracture surface showed no dependence on initial molecular weights for t much greater than tau(r) where t and tau(r) are annealing and relaxation times, respectively. The number of chain bridges crossing a unit area of interface was suggested as the basic molecular property.