微通道中高分子溶液Poiseuille流的耗散粒子动力学模拟

Dissipative particle dynamics simulation of macromolecular solutions under Poiseuille flow in microchannels

利用耗散粒子动力学(dissipative particle dynamics,DPD)方法模拟了微通道中高分子溶液的Poiseuille流动.研究表明,微通道中的高分子溶液呈现非牛顿流体特性,可以用幂律流体来描述流动行为,高分子浓度越大,幂律指数n越小.高分子链与壁面的流体动力学相互作用以及布朗扩散率梯度控制着高分子链的横向迁移.由于传统的DPD方法中壁面诱导的流体动力学作用部分被屏蔽,高分子链将向壁面方向迁移,并且随着流场增强,高分子链向壁面方向迁移越明显.未被屏蔽的流体动力学相互作用和布朗扩散率梯度相互竞争,使高分子链在微通道内的质心分布呈双峰状,通道中心处高分子浓度出现局部最小值.当通道宽度减小、强受限时,壁面与高分子链间的流体动力学相互作用可能全部被屏蔽,而布朗扩散运动弱,高分子向壁面方向有微弱的迁移.

macromolecular solutions under Poiseuille flow in microchannels are investigated using the dissipative particle dynamics （DPD） approach. The results show that the macromolecular solutions are non-Newtonian fluids which can be described by power-law fluids, and the power-law index decreases with the increase of the macromolecular concentration. The DPD simulations show that the hydro- dynamic interaction between the macromolecular chains and the wall, and the gradient of Brownian diffusivity of the chains govern the cross-stream migration of the macromolecules. However, the chain-wall hydrodynamic interaction may not be fully developed and are partly screened in conventional DPD approach. Hence, the chains migrate toward the wall during flow. Simulation results also indicate that the migration toward the wall increases with the increase of the driving force. The competition between the unscreened chain-wall hydrodynamic interaction and Brownian diffusivity leads to two symmetric off-center peaks and a local minimum in the channel centerline in the chain center-of-mass distribution. Under strong confinement, the chain-wall hydrodynamic interaction may be fully screened and the Brownian motion is weak, thus the chains weakly move toward the wall for channel of small width.