title: A computational and experimental study of the linear and nonlinear response of a star polymer melt with a moderate number of unentangled arms.
abstract: We present from simulations and experiments results on the linear and nonlinear rheology of a moderate functionality, low molecular weight unentangled polystyrene (PS) star melt. The PS samples were anionically synthesized and close to monodisperse while their moderate functionality ensures that they do not display a pronounced core effect. We employ a highly coarse-grained model known as Responsive Particle Dynamics where each star polymer is approximated as a point particle. The eliminated degrees of freedom are used in the definition of an appropriate free energy as well as describing the transient pair-wise potential between particles that accounts for the viscoelastic response. First we reproduce very satisfactorily the experimental moduli using simulation. We then consider the nonlinear response of the same polymer melts by implementing a start-up shear protocol for a wide range of shear rates. As in experiments, we observe the development of a stress overshoot with increasing shear rate followed by a steady-state shear stress. We also recover the shear-thinning nature of the melt, although we slightly overestimate the extent of shear-thinning with simulations. In addition, we study relaxations upon the removal of shear where we find encouraging agreement between experiments and simulations, a finding that corroborates our agreement for the linear rheology.
authors.affiliation: Computational Biophysics, University of Twente, P.O. Box 217, 7500 AE, Enschede, The Netherlands.
authors.forename: Barry W
authors.initials: BW
authors.lastname: Fitzgerald
authors.affiliation: Foundation for Research and Technology (FORTH), Institute of Electronic Structure and Laser, Heraklion 71110, Crete, Greece.
authors.forename: Helen
authors.initials: H
authors.lastname: Lentzakis
authors.affiliation: Department of Chemistry, University of Athens, Athens 15771, Greece.
authors.forename: Georgios
authors.initials: G
authors.lastname: Sakellariou
authors.affiliation: Foundation for Research and Technology (FORTH), Institute of Electronic Structure and Laser, Heraklion 71110, Crete, Greece.
authors.forename: Dimitris
authors.initials: D
authors.lastname: Vlassopoulos
authors.affiliation: Computational Biophysics, University of Twente, P.O. Box 217, 7500 AE, Enschede, The Netherlands.
authors.forename: Wim J
authors.initials: WJ
authors.lastname: Briels
mesh_terms: D008962:Models, Theoretical; D011108:Polymers / Q000737:chemistry*; D012212:Rheology
chemical_list: D011108:Polymers