Paper Number
SM20
Session
Polymers Solutions, Melts and Blends
Title
Nonlinear shear rheology of unentangled polystyrene solutions
Presentation Date and Time
October 11, 2022 (Tuesday) 10:30
Track / Room
Track 2 / Sheraton 3
Authors
- Costanzo, Salvatore (Federico II University, Department of Chemical, Materials and Production Engineering)
- Ianniello, Vincenzo (University of Naples, DICMaPI)
- Pasquino, Rossana (DICMaPI, Università degli Studi di Napoli Federico II)
- Grizzuti, Nino (University of Naples Federico II, Chemical, Materials and Industrial Production Engineering)
- Ianniruberto, Giovanni (Federico II University, Department of Chemical, Materials and Production Engineering)
- Marrucci, Giuseppe (Federico II University, Department of Chemical, Materials and Production Engineering)
Author and Affiliation Lines
Salvatore Costanzo, Vincenzo Ianniello, Rossana Pasquino, Nino Grizzuti, Giovanni Ianniruberto and Giuseppe Marrucci
Department of Chemical, Materials and Production Engineering, Federico II University, Naples, Italy
Speaker / Presenter
Ianniruberto, Giovanni
Keywords
polymer melts; polymer solutions
Text of Abstract
We explore the linear and nonlinear shear rheological properties of unentangled linear polystyrene solutions. They are made in a way to attain the same fractional number Z of entanglements of a polystyrene melt with molecular weight equal to 30 kDa. The solutions are prepared by dissolving long polystyrene chains (from 126 kDa to 1000 kDa) in oligostyrene with molecular weight equal to 2 kDa. The volume fraction of long polystyrene in solution is decreased with increasing molecular weight, in order to keep Z at a constant value. The linear viscoelastic spectra of the solutions are well described by the Rouse model incorporating glassy relaxation modes. As expected, the Rouse modulus decreases, and the longest Rouse time increases, by decreasing the volume fraction of the long chain. The combination of low elastic modulus and long relaxation time allows to attain very large values of the Rouse Weissenberg number. Reliable experiments are performed with a cone and partitioned plate geometry. During start-up shear tests, the long chains in solution are markedly aligned and stretched, therefore strain hardening of the transient viscosity is observed. With strong chain alignment, the role of friction reduction clearly emerges. Friction reduction effects appear more complex for unentangled solutions as compared to melts. The reason is that, for solutions, flow also affects hydrodynamic interactions which are absent in melts. During strain hardening, axial force transducer overload is rapidly approached. Before overload occurs, normal stress data indicate that the second normal stress difference is virtually zero. Brownian dynamics simulations based on Rouse chains incorporating finite extensibility are shown to be suitable to describe the macroscopic rheological behaviour of the solutions.