Huang, Qian1; Mednova, Olga3; Rasmussen, Henrik K.5; Skov, Anne Ladegaard7; Almdal, Kristoffer8; Hassager, Ole1
1 Department of Chemical and Biochemical Engineering, Technical University of Denmark2 The Danish Polymer Centre, Department of Chemical and Biochemical Engineering, Technical University of Denmark3 Department of Micro- and Nanotechnology, Technical University of Denmark4 Amphiphilic Polymers in Biological Sensing, Department of Micro- and Nanotechnology, Technical University of Denmark5 Department of Mechanical Engineering, Technical University of Denmark6 Manufacturing Engineering, Department of Mechanical Engineering, Technical University of Denmark7 Centre for oil and gas – DTU, Center, Technical University of Denmark8 Center for Nanostructured Graphene, Center, Technical University of Denmark
The possible existence of a qualitative difference on extensional steady state viscosity between polymer melts and polymer solutions is still an open question. Recent experiments [1-4] showed the extensional viscosity of both polymer melts and solutions decayed as a function of strain rate with an exponent of -0.5. When the strain rate became higher than the order of inverse Rouse time, the polymer solutions showed an upturn [1, 4]. However, in the same regime for polymer melts, the experiments were contrary: some of the experiments showed an upturn [4, 5], while others did not [2, 3]. In order to further investigate the extensional steady state viscosity of polymer melts, we carefully synthesized two monodisperse polystyrenes with molar masses of 248 and 484 kg/mole. The start-up and steady uniaxial elongational viscosity have been measured for the two melts using a filament stretching rheometer. We then compared the measurements with the bi-disperse polystyrene melts made from the above two polymers. The influence and sensitivity of impurities were studied by adding different percentages of 484k into 248k polystyrene melt. Furthermore a polydisperse polystyrene with weight average molecular weight 230 kg/mole was also measured for comparison. Possible reasons for the differences shown in the previously mentioned experiments are discussed.