Rheo-optical characterization of polymer chain uncoil and disentanglement in shear flow

Abstract

Abstract Rheo-optical studies allow the monitoring of rheological properties by indirect measurements of optical properties. For pure polymeric fluids, flow birefringence can be used to quantify the molecular orientation level by the application of shear strain rates. In this work, flow birefringence experiments were carried out with a pure polystyrene under different shear rates, shear cycles, and temperature conditions, in a polarized light optical microscope under controlled shear. The level of orientation and its correlation with the dynamics of uncoil/recoil and disentanglement were analyzed. The expected increase in the orientation level as a function of the increase in the shear rate due to the chain uncoiling was confirmed. Following, the chain orientation level reduces over time, associated with chain disentanglement and its subsequent recoiling. Disentanglement behaves irreversibly, while uncoiling and recoiling are reversible processes. A model is proposed to represent these dynamics.

Keywords

• disentanglement
• polymer chain orientation
• flow birefringence
• rheo-optical measurement
• polystyrene