Abstract:

The stable and clear interface in the microchannel is an important basis for further particle screening. Using the ferrofluid as the core flow and the non-magnetic fluid on both sides as the sheath flow is conducive to microfluidic focusing of particles under magnetic field. This paper is based on the experimental analysis of the ferrofluid-water interface in three-phase laminar microfluidic chip and the solution of the mechanical model. The dimensionless numbers Pe, Bo_m, Ca, We, Re, and the time t_T, t_d, t_i to represent the movement state of the particles at the interface were introduced, and it obtained d/h∝(X/Pe)^0.633~0.852. The effect of each force on the interface was in the order of magnetic force greater than interfacial tension, inertial force, and viscous force. When Q_f/Q_w=2, Q_f=15μL/min, the convective effect was obviously greater than the diffusion effect. In this case, the viscous dissipation effect of particles was small, and the interface was stable at the center of the channel. The diffusion time t_d∝(X/Pe)^0.523~0.872 oscillated violently at the entrance stage, accelerating fluid mixing. Meanwhile, the increase of magnetic field gradient and fluid diffusion velocity will lead to a drastic change in interfacial time t_i∝(X/Pe)^0.778~1.172. When X=225—250 in the middle of the magnetic field, t_T>t_i>t_d, and the screening efficiency of magnetic swimming was the highest.

Key words: microchannels, convective diffusion, magnetic force, interfacial tension, viscous force

摘要：

微通道中稳定、清晰的界面是进行颗粒进一步筛选的重要基础，将磁液作为核心流，非磁液作为鞘流有利于颗粒在外加磁场作用下进行微流控聚焦。本文基于对三相层流微流控芯片中磁液-水界面实验分析和力学模型求解，引入量纲为1数Pe、Bo_m、Ca、W、Re，以及表征界面颗粒运动状态的时间t_T、t_d、t_i，得到d/h∝(X/Pe)^0.633~0.852界面上力的大小依次为：磁力>界面张力>惯性力>黏性力。Q_w/Q_f=2，Q_f=15μL/min时，核心流的黏性耗散影响较小，界面位于通道中心处较为稳定。界面磁颗粒扩散时间t_d∝(X/Pe)^0.523~0.872在入口阶段振荡剧烈，加速流体混合，同时磁场梯度和流体扩散速度的增大会导致界面时间t_i∝(X/Pe)^0.778~1.172剧烈变化，当X=225～250时，t_T>t_i>t_d，颗粒聚焦效率最高。

关键词: 微通道, 对流扩散, 磁力, 界面张力, 黏性力