Nonlinear shear and extensional rheology of entangled polystyrene solutions with linear and star styrene oligomeric solvents

Abstract

It has been reported that the length (molecular weight) of oligomeric solvents has a significant influence on nonlinear rheology of the corresponding polymer solutions. While different explanations, such as flow-induced reduction of monomeric friction or flow-induced phase separation, have been proposed, we show that the influence of oligomeric solvents on nonlinear shear and extensional rheology can be ignored when the length of the oligomers is long enough. We compared three polystyrene (PS) solutions, 600 k-4 k-50%, 600 k-10 k-50%, and 600 k-8a4k-50%, all containing the same weight fraction of the same long PS chains but different styrene oligomeric solvents. The first two contain linear oligomers with different length, while the last two contain oligomers with a similar span length but different molecular architectures (linear and star, respectively). All the solutions show identical nonlinear rheological behavior in startup shear and extensional flows until steady state, and also the same stress relaxation behavior after step shear strain.