  The size of rings (also called cyclic polymers) in bidisperse blends of
chemically identical rings is analyzed by computer simulations. Data of
entangled ring blends and blends of interpenetrating rings are compared and it
is shown that the compression of entangled rings can be explained by the
changes in the penetrable fraction of the minimal surface bounded by the ring.
Corrections for small rings can be approximated by a concatenation probability
$1-P_{OO}$ that a ring entraps at least one other ring. Both results are in
line with a previous work [1] to explain the compression of entangled rings in
monodisperse melts. Bond-bond correlations in melts of interpenetrating rings
lead to similar corrections for ring sizes as reported previously [2] for
monodisperse linear melts. For entangled rings, bond-bond correlations show an
anti-correlation peak at a curvilinear distance of about ten segments that
coincides with a horizontal tangent in the normalized mean square internal
distances along the ring. Both observations become independent of melt
molecular weight for sufficiently large degrees of polymerization and such
behavior is not found in samples with entanglements switched off. In
consequence, the length scale of topological interactions (entanglement length)
in a melt of entangled rings must be considered as constant in contrast to a
recent proposal by Sakaue [3].
