Brownian dynamics simulation of linear polymers under elongational flow: Beadrod model with hydrodynamic interactions
Abstract
Brownian dynamics (BD) simulations of a linear freely jointed beadrod polymer chain with excluded volume (EV) interaction have been performed under elongational flow with and without the use of fluctuating hydrodynamic interactions (HI). The dependence of the chain size, shape and intrinsic elongational viscosity on the elongational rate ɛ˙ are reported. A sharp coilstretch transition is observed when ɛ˙ exceeds a critical value, ɛ˙_{c}. The inclusion of the HI leads to a shift in the coilstretch transition to higher flow values. Chain deformation due to elongational flow is observed to first consist of the alignment of the chain with the direction of flow without significant chain extension followed by additional alignment of the bond vectors with the flow direction and chain extension as flow rate is increased further. The distribution function for the chain's radius of gyration becomes significantly broader within the transition region which implies an increase in fluctuations in the chain size in this region. The structure factors parallel and perpendicular to the flow direction illustrate different elongational rate dependencies. At high rates, the structure factor in the direction of the flow exhibits an oscillating dependence which corresponds to the theoretically predicted shape for a rigidrod model. The mean squared orientation of each bond within the chain with respect to the flow direction as function of bond number is nearly parabolic in shape with the highest degree of orientation found within the chain's interior. The dependence of the critical elongational rate, ɛ˙_{c}, on the chain length, N, is observed to be ɛ˙_{c}∼N^{1.96} when hydrodynamic interactions are not employed and ɛ˙_{c}∼N^{1.55} when they are invoked. These scaling exponents agree well with those obtained in previous BD simulations of beadFENE (i.e., finitely extensible nonlinear elastic) spring chains as well as with the theoretical predictions of ɛ˙_{c}∼N^{2} and ɛ˙_{c}∼N^{1.5} without and with hydrodynamic interactions based on the Rouse and Zimm models, respectively.
 Publication:

Journal of Chemical Physics
 Pub Date:
 August 2002
 DOI:
 10.1063/1.1493187
 Bibcode:
 2002JChPh.117.4030N
 Keywords:

 polymers;
 digital simulation;
 Brownian motion;
 hydrodynamics;
 nonNewtonian flow;
 fluctuations;
 Brownian Movements;
 Digital Simulation;
 Hydrodynamics;
 Molecular Dynamics;
 Nonnewtonian Flow;
 Variations;
 47.50.+d;
 05.40.Jc;
 83.10.Mj;
 Fluid Mechanics and Thermodynamics;
 Brownian motion;
 Molecular dynamics Brownian dynamics