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
η
0,linear
to their ring counterparts
η
0,ring
at isofrictional conditions is discussed as function of the number of entanglements
Z
. In the unentangled regime
η
0,linear
/η
0,ring
is virtually constant, consistent with the earlier data, atomistic simulations, and the theoretical expectation
η
0,linear
/η
0,ring
=2
. In the entanglement regime, the
Z
-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,
η
0,linear
/η
0,ring
~
Z
1.2±0.3,
is weaker than the scaling prediction (
η
0,linear
/η
0,ring
~
Z
1.6±0.3
) and the simulations (
η
0,linear
/η
0,ring
~
Z
2.0±0.3
). 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.