Brownian dynamics simulations of a flexible polymer chain which includes continuous resistance and multibody hydrodynamic interactions

摘要

Using methods adapted from the simulation of suspension dynamics,we have developed a Brownian dynamics algorithm with multibody hydrodynamic interactions for simulating the dynamics of polymer molecules.The polymer molecule is modeled as a chain composed of a series of inextensible,rigid rods with constraints at each joint to ensure continuity of the chain.The linear and rotational velocities of each segment of the polymer chain are described by the slender-body theory of Batchelor[J.Fluid Mech.44,419(1970)].To include hydrodynamic interactions between the segments of the chain,the line distribution of forces on each segment is approximated by making a Legendre polynomial expansion of the disturbance velocity on the segment,where the first two terms of the expansion are retained in the calculation.Thus,the resulting linear force distribution is specified by a center of mass force,couple,and stresslet on each segment.This method for calculating the hydrodynamic interactions has been successfully used to simulate the dynamics of noncolloidal suspensions of rigid fibers[O.G.Harlen,R.R.Sundararajakumar,and D.L.Koch,J.Fluid Mech.388,355(1999);J.E.Butler and E.S.G.Shaqfeh,J.Fluid Mech.468,204(2002)].The longest relaxation time and center of mass diffusivity are among the quantities calculated with the simulation technique.Comparisons are made for different levels of approximation of the hydrodynamic interactions,including multibody interactions,two-body interactions,and the "freely draining" case with no interactions.For the short polymer chains studied in this paper,the results indicate a difference in the apparent scaling of diffusivity with polymer length for the multibody versus two-body level of approximation for the hydrodynamic interactions.