Viscosity of Ring Polymer Melts

Abstract

We have measured the linear rheology of critically purified ring polyisoprenes, polystyrenes and polyethyleneoxides of different molar masses. The ratio of the zero-shear viscosities of linear polymer melts <i>η_0,linear</i> to their ring counterparts <i>η_0,ring</i> at isofrictional conditions is discussed as function of the number of entanglements <i>Z</i>. In the unentangled regime <i>η_0,linear/η_0,ring</i> is virtually constant, consistent with the earlier data, atomistic simulations, and the theoretical expectation <i>η_0,linear/η_0,ring=2</i>. In the entanglement regime, the <i>Z</i>-dependence of rings viscosity is much weaker than that of linear polymers, in qualitative agreement with predictions from scaling theory and simulations. The power-law extracted from the available experimental data in the rather limited range 1<Z<20, <i>η_0,linear/η_0,ring</i> ~ <i>Z^1.2±0.3,</i> is weaker than the scaling prediction (<i>η_0,linear/η_0,ring</i> ~ <i>Z^1.6±0.3</i> ) and the simulations (<i>η_0,linear/η_0,ring</i> ~ <i>Z^2.0±0.3</i> ). Nevertheless, the present collection of state-of-the- art experimental data unambiguously demonstrates that rings exhibit a universal trend clearly departing from that of their linear counterparts, and hence it represents a major step toward resolving a 30-year old problem.