Behaviors of a Polymer Chain in Channels: From Zimm to Rouse Dynamics

Abstract

The effects of confinement and hydrodynamic interactions on single-chain diffusion behaviors are studied by using a combination of molecular dynamics and multiparticle collision dynamics simulations. For polymers in free space, the simulation results showed that the diffusion coefficient D ∞ for long chains scales with the chain length N as D ∞ ∼ N –ν (ν = 0.588), consistent with the Zimm dynamics, but it deviates from the Zimm dynamics for short chains. For polymers confined in channels with width H, the diffusion coefficient is found to follow two different scaling relations. The observed behaviors could be understood by introducing a microscopic hydrodynamic length ξh, below which the overall effect of hydrodynamic interactions becomes less important. For a confined chain, the diffusion behavior exhibits a crossover from Zimm (nondraining) to Rouse (free draining) dynamics as the channel size H decreases. When H is larger than ξh, the confinement experienced by the polymer chain is weak and the diffusion coefficient scales as D ∼ H 0.7, in accordance with the prediction of blob theory; when H is smaller than ξh, D becomes independent of H, implying a free draining condition. A general analytical expression of D is derived by extending the partially permeable sphere model to the blob scale, which gives a quantitative description of the transition from Zimm to Rouse dynamics as H decreases.

Lock-key microfluidics: simulating nematic colloid advection along wavy-walled channels

“…To simulate colloids in a flowing and thermally fluctuating nematic liquid crystal confined within a complex channel, a multi-particle collision dynamics (MPCD) algorithm is used. 39–42 MPCD has been employed to simulate reaction–diffusion dynamics, 43,44 electrophoresis, 45,46 thermophoresis, 47 swimmers, 48–50 polymers, 51–54 colloidal suspensions, 55,56 binary mixtures, 57 viscoelastic fluids, 58 ferrofluids, 59,60 and dense stellar systems. 61–63 Most relevantly, MPCD has been used to simulate nematic liquid crystals.…”