
J.U. Sommer, K. Saalwächter.
Segmental Order in Endlinked Polymer Networks: A Monte Carlo Study
Eur. Phys. J. E.
Accepted.
Abstract
Segmental order in endlinked monomodal and bimodal polymer networks is
investigated by means of bondfluctuation MonteCarlo simulations. The tensor
order parameter, which is a central observable in NMR experiments, is not
uniquely related to simple vectorial order. The relaxation of NMRdetected
tensorial interactions towards their finite longtime limit is best described by
a power law and occurs over much longer timescales than the relaxation of
vectorial order. The wellknown prediction for the segmental order of Gaussian
chains as a simple function of the segment number between constraints is not
straightforwardly obeyed, neither in dry nor in swollen networks. Excluded
volume interactions tend to significantly reduce the tensorial order, as is
clearly observed in singlechain simulations. A distribution extends along the
chain, where order is increased in a region of 3040 bonds around the crosslinks
in networks. The dominating contribution to the order parameter distribution
arises from the frozenin distribution of endtoend separations. We find strong
deviations from the Gamma distribution, which has so far been implicitly used in
most NMR works, as it is a straightforward consequence of a Gaussian
distribution of end separations. Specifically, we find narrower distributions,
as small values of the tensor order parameter are strongly suppressed, most
probably as a result of trapped entanglements. The markedly subaffine behavior
of the average order parameter and the changes in its distribution on swelling
is assigned to orientation processes of strands which compensate for the
nonaffine local deformation. Our central observations and interpretations are
well supported by our previous experimental and theoretical work.
Close window