**Molecular dynamics simulations of supramolecular polymer rheology**

ZL Li and H Djohari and EE Dormidontova, JOURNAL OF CHEMICAL PHYSICS, 133, 184904 (2010).

DOI: 10.1063/1.3498781

Using equilibrium and nonequilibrium molecular dynamics simulations, we
studied the equilibrium and rheological properties of dilute and
semidilute solutions of head-to-tail associating polymers. In our
simulation model, a spontaneous complementary reversible association
between the donor and the acceptor groups at the ends of oligomers was
achieved by introducing a combination of truncated pseudo-Coulombic
attractive potential and Lennard Jones repulsive potential between
donor, acceptor, and neighboring groups. We have calculated the
equilibrium properties of supramolecular polymers, such as the
ring/chain equilibrium, average molecular weight, and molecular weight
distribution of self-assembled chains and rings, which all agree well
with previous analytical and computer modeling results. We have
investigated shear thinning of solutions of 8- and 20-bead associating
oligomers with different association energies at different temperatures
and oligomer volume fractions. All reduced viscosity data for a given
oligomer length can be collapsed into one master curve, exhibiting two
power-law regions of shear-thinning behavior with an exponent of -0.55
at intermediate ranges of the reduced shear rate beta and -0.8 (or -0.9)
at larger shear rates. The equilibrium viscosity of supramolecular
solutions with different oligomer lengths and associating energies is
found to obey a power-law scaling dependence on oligomer volume fraction
with an exponent of 1.5, in agreement with the experimental observations
for several dilute or semidilute solutions of supramolecular polymers.
This implies that dilute and semidilute supramolecular polymer solutions
exhibit high polydispersity but may not be sufficiently entangled to
follow the reptation mechanism of relaxation. (C) 2010 American
Institute of Physics. **doi:10.1063/1.3498781**

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