Opening the Pandora's box to understand flow behavior of polymeric fluids.

Structure-property relationship has been explored for decades in the context of flow behavior of entangled polymeric liquids. For a long time, it has been assumed that the structure of an entangled polymer, i.e., the entanglement network would experience smooth changes during flow. Using an effective particle-tracking velocimetric (PTV) method recently developed in our lab [1], we found that the nonlinear flow dynamics are associated with an elastic breakdown of the fluid structure. This cohesive failure does not necessarily occur homogeneously in a macroscopic-scale experiment, making it ambiguous to interpret traditional rheological measurements. The presentation complies a whole set of PTV observations to elucidate the physical origin of nonlinear flow phenomena in complex fluids such as polymers. [1] \textit{Phys. Rev. Lett. }\textbf{96}, 016001 (2006); \textit{ibid}. \textbf{96}, 196001; \textit{ibid.} \textbf{97}, 187801.