Time and length scales of polymer melts studied by coarse-grained molecular dynamics simulations
Journal of Chemical Physics
Effects of alignment layer thickness on the pretilt angle of liquid crystals APL: Org. Electron. Photonics 3, 270 (2010) Effects of alignment layer thickness on the pretilt angle of liquid crystals Appl. Phys. Lett. 97, 243306 (2010) Field-theoretic model of inhomogeneous supramolecular polymer networks and gels J. Chem. Phys. 133, 174903 (2010) Origin of translocation barriers for polyelectrolyte chains JCP: BioChem. Phys. 3, 11B610 (2009) Origin of translocation barriers for polyelectrolyte
... r polyelectrolyte chains We present coarse-grained molecular dynamics simulations of linear polyethylene ͑PE͒ melts, ranging in chain length from C 80 to C 1000 . The employed effective potentials, frictions, and random forces are all derived from detailed molecular dynamics simulations, leaving no adjustable parameters. Uncrossability constraints are introduced in the coarse-grained model to prevent unphysical bond crossings. The dynamic and zero-shear rate rheological properties are investigated and compared with experiment and other simulation work. In the analysis of the internal relaxations we identify a new length scale, called the slowing down length N s , which is smaller than the entanglement length N e . The effective segmental friction rapidly increases around N s leading, at constant density, to a transition in the scaling of the diffusion coefficient from DϳN Ϫ1 to D ϳN Ϫ2 , a transition in the scaling of the viscosity from ϳN to ϳN 1.8 , and conspicuous nonexponential relaxation behavior. These effects are attributed to strong local kinetic constraints caused by both chain stiffness and interchain interactions. The onset of nonlocal ͑entanglement͒ effects occurs at a chain length of C 120 . Full entanglement effects are observed only above C 400 , where the shear relaxation modulus displays a plateau and the single chain coherent dynamic structure factor agrees with the reptation model. In this region the viscosity scales as ϳN 3.6 , the tube diameter is dϷ5.4 nm, the entanglement molecular weight is M e Ϸ1700 g/mol, and the plateau modulus is G N 0 Ϸ2.4 MPa, all in good agreement with experimental data.