Effective Entanglement and Constraint Release in Deformed Polymer Melts

Quantifying the response of entangled polymers to large and rapid deformations presents a great challenge in polymer physics. With simulation results, we identify the effective entanglement that governs the chain conformation and rheological response of deformed entangled polymers. The distribution of effective entanglements gives a natural estimation of the mean survival tube. The constraint release caused by the motion of effective entanglements well describes the relaxation process after step elongation within the framework of the tube model. The relation between the dynamics of effective entanglements and other motions, including the orientation, stretch, and retraction of chain segments, is examined. Additionally, with small-angle neutron scattering, we experimentally explored the effective entanglements during the relaxation of an elongated polystyrene melt. We observe a "Rouse ramp" in the decay of effective entanglements, which is considered a key feature of the tube relaxation induced by the constraint release.