title: Determination of linear viscoelastic properties of an entangled polymer melt by probe rheology simulations.
abstract: Particle rheology is used to extract the linear viscoelastic properties of an entangled polymer melt from molecular dynamics simulations. The motion of a stiff, approximately spherical particle is tracked in both passive and active modes. We demonstrate that the dynamic modulus of the melt can be extracted under certain limitations using this technique. As shown before for unentangled chains [Karim et al., Phys. Rev. E 86, 051501 (2012)PLEEE81539-375510.1103/PhysRevE.86.051501], the frequency range of applicability is substantially expanded when both particle and medium inertia are properly accounted for by using our inertial version of the generalized Stokes-Einstein relation (IGSER). The system used here introduces an entanglement length d_{T}, in addition to those length scales already relevant: monomer bead size d, probe size R, polymer radius of gyration R_{g}, simulation box size L, shear wave penetration length Δ, and wave period Λ. Previously, we demonstrated a number of restrictions necessary to obtain the relevant fluid properties: continuum approximation breaks down when d≳Λ; medium inertia is important and IGSER is required when R≳Λ; and the probe should not experience hydrodynamic interaction with its periodic images, L≳Δ. These restrictions are also observed here. A simple scaling argument for entangled polymers shows that the simulation box size must scale with polymer molecular weight as M_{w}^{3}. Continuum analysis requires the existence of an added mass to the probe particle from the entrained medium but was not observed in the earlier work for unentangled chains. We confirm here that this added mass is necessary only when the thickness L_{S} of the shell around the particle that contains the added mass, L_{S}>d. We also demonstrate that the IGSER can be used to predict particle displacement over a given timescale from knowledge of medium viscoelasticity; such ability will be of interest for designing nanoparticle-based drug delivery.
authors: Department of Chemical Engineering, Texas Tech University, Box 43121, Lubbock, Texas 79409, USA.
authors: Mir
authors: M
authors: Karim
authors: Center for Molecular Study of Condensed Soft Matter, and Department of Chemical and Biological Engineering, Illinois Institute of Technology, 3440 S. Dearborn Street, Chicago, Illinois 60616, USA.
authors: Tsutomu
authors: T
authors: Indei
authors: Center for Molecular Study of Condensed Soft Matter, and Department of Chemical and Biological Engineering, Illinois Institute of Technology, 3440 S. Dearborn Street, Chicago, Illinois 60616, USA.|Department of Physics, Illinois Institute of Technology, 3101 South Dearborn Street, Chicago, Illinois 60616, USA.|Department of Applied Mathematics, Illinois Institute of Technology, 10 West 32nd Street, Chicago, Illinois 60616, USA.
authors: Jay D
authors: JD
authors: Schieber
authors: Department of Chemical Engineering, Texas Tech University, Box 43121, Lubbock, Texas 79409, USA.
authors: Rajesh
authors: R
authors: Khare