Watching nucleation and growth of chain disentanglement in large-amplitude oscillatory shear of entangled polymer solutions
Our recent stress-controlled measurements show that a sufficient yet moderate level of chain deformation due to shear can produce spatial topological rearrangement to free chains from mutual dynamic constraint . The chain disentanglement seems to occur catastrophically, resulting in an inhomogeneously sheared sample during rate-controlled shear . Thus, chain disentanglement is also expected to take place during large amplitude oscillatory shear (LAOS) at frequencies higher than the overall chain relaxation rate. We applied our particle-tracking velocimetric technique to probe the state of chain entanglement during LAOS. We found that the chain orientation produced by LAOS led to a new environment in which the initially well-entangled chains managed to disentangle inhomogeneously in space. A layer free of chain entanglement developed to take the load of the imposed strain. As a result of this nonlinearity, the rest of the sample avoided significant deformation and its chain entanglement remained intact.  Tapadia, P.; Wang, S. Q. Phys Rev. Lett, 91, 198301 (2003); Tapadia, P.; Wang, S. Q. Macromolecules 37, 9083 (2004).  Tapadia, P.; Wang, S. Q. Phys. Rev. Lett. , in press (2005).
Wang, Shi-Qing, "Watching nucleation and growth of chain disentanglement in large-amplitude oscillatory shear of entangled polymer solutions" (2006). Polymer Science Faculty Research. 579.