Three-dimensional diamagnetic particle deflection in ferrofluid microchannel flows

Abstract

Magnetic field-induced particle manipulation is a promising technique for biomicrofluidics applications. It is simple, cheap, and also free of fluid heating issues that accompany other common electric, acoustic, and optical methods. This work presents a fundamental study of diamagnetic particle motion in ferrofluid flows through a rectangular microchannel with a nearby permanent magnet. Due to their negligible magnetization relative to the ferrofluid, diamagnetic particles experience negative magnetophoresis and are repelled away from the magnet. The result is a three-dimensionally focused particle stream flowing near the bottom outer corner of the microchannel that is the farthest to the center of the magnet and hence has the smallest magnetic field. The effects of the particle's relative position to the magnet, particle size, ferrofluid flow rate, and concentration on this three-dimensional diamagnetic particle deflection are systematically studied. The obtained experimental results agree quantitatively with the predictions of a three-dimensional analytical model.

Numerical Investigation on Heat and Flow Characteristics of Temperature-Sensitive Ferrofluid in a Square Cavity

“…The ferrofluid generally consisted of magnetite nanosized particle of around 1 to 100 nm and carrier liquid such as water, oils, and hydrocarbons with the aid of surfactants in a continuous carrier phase. It can be controlled by both magnitude and direction of an external magnetic field and temperature [1][2][3][4][5][6][7][8][9][10][11][12]. In addition, because of the nanosized magnetic particles consisting of the ferrofluids and the surfactant attached to magnetic particles, the ferrofluid could be prevented from particles sticking to each other or precipitate with Brownian motion [2].…”

Continuous sheath-free magnetic separation of particles in a U-shaped microchannel

“…This is a consequence of positive magnetophoresis, which is astonishing because polystyrene particles have been previously found to behave diamagnetic in ferrofluids by multiple research groups, [32][33][34][35][36][37] including ours. 30,38,39 Such a counterintuition phenomenon becomes much more obvious in Figure 3(b), where the particle mixture migrates in a focused stream adjacent to the channel sidewall nearer to the magnet as a result of the positive magnetophoretic deflection. We speculate that these observed "pseudomagnetic" polystyrene particles are formed due to the attachment of magnetic nanoparticles (the content of the suspending ferrofluid) onto their surfaces, which has been reported in a recent experiment.…”

Continuous-flow ferrohydrodynamic sorting of particles and cells in microfluidic devices

“…Pamme's group demonstrated continuous particle and cell manipulation using paramagnetic salt solution in microfluidic devices (Peyman et al 2009;Rodriguez-Villarreal et al 2011). Xuan's group studied the transport of particles in both paramagnetic solutions and ferrofluids through a rectangular microchannel embedded with permanent magnets (Liang et al 2011;Zhu et al 2012). Park's group recently sorted human histolytic lymphoma monocytes cells from red blood cells using gadolinium diethylenetriamine pentaacetic acid (Gd-DTPA) solution (Shen et al 2012).…”