Molecular dynamics study of the flow properties of a polymeric liquid confined by a soft substrate

CLAUDIO PASTORINO; KURT BINDER; MARCUS MÜLLER

Génova, Italia

Conferencia; International Conference on Statistical Physics (Stat Phys 23); 2007

IUPAP

We studied the  flow properties of a polymer melt  confined between  polymerbrush layers, by means of molecular dynamics simulations. The brush serves asa model of a soft, deformable and elastic substrate whose properties are tunedin the simulation changing the grafting density. Brush and polymer melt arecomposed of 10-bead chains of identical chemical identity and modeled withwell-established coarse-grained potentials that retain the main properties ofthe chains. The temperature is held constant with a Dissipative ParticleDynamics thermostat that keeps the hydrodynamic correlations in the system.Moving the confining walls at constant velocity or applying an external volumeforce, Couette and Poiseuille flows are imposed to the system and  thevelocity and density profiles are obtained from the simulations, as a functionof shear rate or external force. Boundary conditions (slip length andvelocity) of this non-newtonian liquid are measured directly from thesimulations, as function of the grafting density of the brush layer.  Thecharacteristics of the brush-melt interface, morphology and dynamics ofthe chains are also obtained. We observe an interesting inversion of the flow velocityin the vicinity of the brush-melt interface, due to non-trivial cyclic dynamics of the graftedchains.