Rivalry of diffusion, external field and gravity in micro-convection of magnetic colloids

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS

卷:498

Article

Kitenbergs, Guntars¹  Cebers, Andrejs¹ 

[1] Univ Latvia, MMML Lab, Jelgavas 3, LV-1004 Riga, Latvia

关键词: Colloids;    Micro-convection;    Gravity effects;    Microfluidics;   

DOI  :  10.1016/j.jmmm.2019.166247

来源: Elsevier

【 摘 要 】

Magnetic fields and magnetic materials have promising microfluidic applications. For example, magnetic micro-convection can enhance mixing considerably. However, previous studies have not explained increased effective diffusion during this phenomenon. Here we show that enhanced interface smearing comes from a gravity induced convective motion within a thin microfluidic channel, caused by a small density difference between miscible magnetic and non-magnetic fluids. This motion resembles diffusive behavior and can be described with an effective diffusion coefficient. We explain this with a theoretical model, based on a dimensionless gravitational Rayleigh number, and verify it by numerical simulations and experiments with different cell thicknesses. Results indicate the applicability and limitations for microfluidic applications of other colloidal systems. Residual magnetic micro-convection follows earlier predictions.

【 授权许可】

Free