Patrick Ahlrichs | Searcharxiv

arXiv2000

Screening of Hydrodynamic Interactions in Semidilute Polymer Solutions: A Computer Simulation Study

We study single-chain motion in semidilute solutions of polymers of length N = 1000 with excluded-volume and hydrodynamic interactions by a novel algorithm. The crossover length of the transition from Zimm (short lengths and times) to Rouse dynamics (larger scales) is proportional to the static screening length. The crossover time is the corresponding Zimm time. Our data indicate Zimm behavior at large lengths but short times. There is no hydrodynamic screening until the chains feel constraints, after which they resist the flow: "Incomplete screening" occurs in the time domain.

cond-mat.soft↗

arXiv1999

Simulation of a Single Polymer Chain in Solution by Combining Lattice Boltzmann and Molecular Dynamics

In this paper we establish a new efficient method for simulating polymer-solvent systems which combines a lattice Boltzmann approach for the fluid with a continuum molecular dynamics (MD) model for the polymer chain. The two parts are coupled by a simple dissipative force while the system is driven by stochastic forces added to both the fluid and the polymer. Extensive tests of the new method for the case of a single polymer chain in a solvent are performed. The dynamic and static scaling properties predicted by analytical theory are validated. In this context, the influence of the finite size of the simulation box is discussed. While usually the finite size corrections scale as L^{-1} (L denoting the linear dimension of the box), the decay rate of the Rouse modes is only subject to an L^{-3} finite size effect. Furthermore, the mapping to an existing MD simulation of the same system is done so that all physical input values for the new method can be derived from pure MD simulation. Both methods can thus be compared quantitatively, showing that the new method allows for much larger time steps. Comparison of the results for both methods indicates systematic deviations due to non-perfect match of the static chain conformations.

cond-mat.soft↗