title: Scale-free center-of-mass displacement correlations in polymer melts without topological constraints and momentum conservation: a bond-fluctuation model study.
abstract: By Monte Carlo simulations of a variant of the bond-fluctuation model without topological constraints, we examine the center-of-mass (COM) dynamics of polymer melts in d = 3 dimensions. Our analysis focuses on the COM displacement correlation function C(N)(t)≈∂(t) (2)h(N)(t)/2, measuring the curvature of the COM mean-square displacement h(N)(t). We demonstrate that C(N)(t) ≈ -(R(N)∕T(N))(2)(ρ∗/ρ) f(x = t/T(N)) with N being the chain length (16 ≤ N ≤ 8192), R(N) ∼ N(1/2) is the typical chain size, T(N) ∼ N(2) is the longest chain relaxation time, ρ is the monomer density, ρ(*)≈N/R(N) (d) is the self-density, and f(x) is a universal function decaying asymptotically as f(x) ∼ x(-ω) with ω = (d + 2) × α, where α = 1/4 for x ≪ 1 and α = 1/2 for x ≫ 1. We argue that the algebraic decay NC(N)(t) ∼ -t(-5/4) for t ≪ T(N) results from an interplay of chain connectivity and melt incompressibility giving rise to the correlated motion of chains and subchains.
authors.affiliation: Institut Charles Sadron, Université de Strasbourg, CNRS, 23 rue du Loess, 67037 Strasbourg Cedex, France. joachim.wittmer@ics-cnrs.unistra.fr
authors.forename: J P
authors.initials: JP
authors.lastname: Wittmer
authors.forename: P
authors.initials: P
authors.lastname: Polińska
authors.forename: H
authors.initials: H
authors.lastname: Meyer
authors.forename: J
authors.initials: J
authors.lastname: Farago
authors.forename: A
authors.initials: A
authors.lastname: Johner
authors.forename: J
authors.initials: J
authors.lastname: Baschnagel
authors.forename: A
authors.initials: A
authors.lastname: Cavallo
mesh_terms: D000465:Algorithms; D004058:Diffusion; D056004:Molecular Dynamics Simulation; D009010:Monte Carlo Method; D011108:Polymers / Q000737:chemistry*
chemical_list: D011108:Polymers