Matsumiya, Yumi5; Masubuchi, Yuichi5; Watanabe, Hiroshi5; Huang, Qian1; Rasmussen, Henrik K.3; Javier Alvarez, Nicolas1; 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 Mechanical Engineering, Technical University of Denmark4 Manufacturing Engineering, Department of Mechanical Engineering, Technical University of Denmark5 unknown
For an entangled solution of linear polystyrene (PS 545k; M = 545k) in dibutyl phthalate (DBP), the stress relaxation after constant-rate uniaxial elongation was examined with an extensional viscosity fixture mounted on ARES (TA Instruments). The PS concentration, c = 52 wt%, was chosen in a way that the entanglement density M/Me of the solution coincided with that of PS 290k melt (M = 290k). After the elongation at the Rouse-based Weissenberg number Wi(R) ~ 3 up to the Hencky strain of 3, the short time stress relaxation of the solution was accelerated by a factor of ~4, which was less significant compared to the acceleration (by a factor of ~ 10) noted for PS melt under a similar condition. This result, being in harmony with the mild acceleration found for a 52 wt% blend of PS 545k with an oligomeric styrene (M = 1k), suggested that the segmental friction is reduced when the chain is highly stretched and oriented but this reduction weakens on an increase of the concentration of un-stretchable solvent molecules. This change of the stretch/orientation reduction of the friction with the solvent concentration appears to be consistent with the monotonic thinning of the steady-state elongational viscosity seen for melts and the lack of monotonic thinning observed for the semidilute solutions. Results for less concentrated solutions will be also presented on site.
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85th Annual Meeting of The Society of Rheology, 2013