PHASE-ANGLE EFFECTS ON FRACTURE-TOUGHNESS OF POLYMER INTERFACES REINFORCED WITH BLOCK-COPOLYMERS

The effect of the phase angle psi on fracture toughness and fracture m echanisms of planar interfaces between polystyrene (PS) and poly(2-vin ylpyridine) (PVP) reinforced with deuterium-labeled polystyrene (dPS)/ PVP block copolymers was investigated using an asymmetric double canti lever beam (ADCB) specimen. The fracture toughness of an interfacial c rack, G(c), was measured as a function of the phase angle psi, the are al chain density of the block copolymer SIGMA, and the degree of polym erization N of the chains. The fracture mechanisms of the interface we re studied by forward recoil spectrometry (FRES), which permitted the location of the dPS block to be determined after fracture. There is a dramatic change in fracture toughness as the phase angle changes sign, a change which is associated with the formation of crazes in the PS a t, and away from, the interface. The angle theta of craze propagation away from the interface depends on the phase angle psi. For positive p hase angles, theta is close to 45-degrees; for negative phase angles, theta is close to 135-degrees.