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Abstract:
The bond fluctuation method is used to simulate both
nonconcatenated entangled and interpenetrating melts of ring polymers. We
find that the swelling of interpenetrating rings upon dilution follows the same
laws as for linear chains. Knotting and linking probabilities of ring polymers in
semidilute solution are analyzed using the HOMFLY polynomial. We find an
exponential decay of the knotting probability of rings. The correlation length of
the semidilute solution can be used to superimpose knotting data at different
concentrations. A power law dependence f n ∼ ϕR2 ∼ ϕ0.77N for the average
number f n of linked rings per ring at concentrations larger than the overlap
volume fraction of rings ϕ* is determined from the simulation data. The fraction
of nonconcatenated rings displays an exponential decay POO ∼ exp(−f n), which
indicates f n to provide the entropic effort for not forming concatenated
conformations. On the basis of these results, we find four different regimes for
the conformations of rings in melts that are separated by a critical lengths NOO, NC, and N*. NOO describes the onset of the effect
of nonconcatenation below which topological effects are not important, NC is the crossover between weak and strong
compression of rings, and N* is defined by the crossover from a nonconcatenation contribution f n ∼ ϕR2 to an overlap
dominated concatenation contribution f n ∼ ϕN1/2 at N > N*. For NOO < N < NC, the scaling of ring sizes R ∼ N2/5 results from
balancing nonconcatenation with weak compression of rings. For NC < N < N*, nonconcatenation and strong compression imply
R ∼ N3/8. Our simulation data for noninterpenetrating rings up to N = 1024 are in good agreement with the prediction for weakly compressed rings.
