Effects of particles on stability of flow-induced precursors

The effect of two colorant particles with different surface geometries on the stability of shear-induced precursors in isotactic polypropylene was studied after the cessation of shear flow at 140 °C. In the absence of particles, the shear-induced precursors survived for at least 100 s after the shear flow ended. The presence of particles was found to stabilize lower molecular weight chains assisting in the formation of additional shear-induced precursors. The precursors thus formed in the samples containing particles contained two oriented clusters with different molecular weights. Incorporation of lower molecular weight chains in the precursors led to increased dissolution rates of the shear-induced precursors. Particle surface geometry was found to influence precursor dissolution, with planar particles stabilizing the shear-induced precursors to a much greater extent than curved particles. The particles investigated thus act like structural probes to follow quantitatively the dissolution process of precursors after shear and importantly to infer the formation of precursors during shear.