Molecular dynamics simulations of the chain dynamics in monodisperse oligomer melts and of the oligomer tracer diffusion in an entangled polymer matrix.
The apparent analogy between the self-diffusion of linear oligomers in monodisperse systems, 2 up to 32 monomers, and their tracer diffusion in an entangled polymer matrix of length 256 is investigated by molecular dynamics simulations at constant pressure. Oligomers and polymers are represented by the same coarse-grained (bead-spring) model. An analysis based on the Rouse model is presented. The scaling relationship of the self-diffusion coefficient D with the chain length N written as D proportional, variantN(-alpha) is analyzed for a wide range of temperatures down to the glass transition temperature T(g). Near T(g), the heterogeneous dynamics is explored by the self-part of the van Hove distribution function and various non-Gaussian parameters. For the self-diffusion in a monodisperse system a scaling exponent alpha(T)>1 depending on temperature is found, whereas for the tracer diffusion in an entangled matrix alpha=1 is obtained at all temperatures, regardless of the oligomer length. The different scaling behavior between both systems is explained by a different monomer mobility, which depends on chain length for monodisperse systems, but is constant for all tracers in the polymer matrix.
Durand
M
M
Institut Charles Sadron, CNRS, 23 Rue du Loess-BP 84047, 67034 Strasbourg Cedex 2, France. manuel.durand@ics-cnrs.unistra.fr
Meyer
H
H
Benzerara
O
O
Baschnagel
J
J
Vitrac
O
O
D004058:Diffusion; D056004:Molecular Dynamics Simulation; D011108:Polymers / Q000737:chemistry*; D011312:Pressure; D013696:Temperature
D011108:Polymers