Molecular dynamics simulations of the chain dynamics in monodisperse oligomer melts and of the oligomer tracer diffusion in an entangled polymer matrix

• Published in: The Journal of chemical physics 2010-05, Vol.132 (19), p.194902-194902-10
• Main Authors: Durand, M., Meyer, H., Benzerara, O., Baschnagel, J., Vitrac, O.
• Format: Article
• Language: English
• Subjects: Diffusion; Life Sciences; Molecular Dynamics Simulation; Polymers - chemistry; Pressure; Temperature
• ISSN: 0021-9606; 1089-7690
• DOI: 10.1063/1.3420646

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 ∝ N − α 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 α ( T ) > 1 depending on temperature is found, whereas for the tracer diffusion in an entangled matrix α = 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.