Use of Paired, Bonded NdFeB Magnets in Redox Magnetohydrodynamics

Abstract

Bonded neodymium-iron-boron (NdFeB) permanent magnets in a paired configuration were successfully used to control mass transport in redox-based, magnetohydrodynamics (MHD). Control of fluid flow based on magnetic fields has potential for use in portable lab-on-a-chip (LOAC) and analytical devices. Bonded magnets, composed of magnetic powder and organic binder materials, are less expensive and easier to fabricate and pattern than electromagnets and sintered permanent magnets, which have been previously used in MHD studies on electrochemical systems. The ability to pattern bonded magnets near and around the electrodes is expected to allow for better control over the magnetic field distribution and solution flow. Current was generated at an 800-microm-radius platinum disk electrode in a solution of 0.06 M nitrobenzene and 0.5 M tetra-n-butylammonium hexafluorophosphate in acetonitrile. Increases in limiting current in the presence of the magnetic field, which indicate enhancement in mass transport, for sintered (210+/-14%, N = 4, where B(r) = 1.23 T and magnetic field strength is 0.55 T) and bonded (94+/-8%, N = 4, where B(r) = 0.41 T and magnetic field strength is 0.20 T) magnets, were similar to those obtained using an electromagnet with the same magnetic flux densities. The magnetic field strength and not the magnet type is important in controlling fluid flow, which is encouraging for integration of bonded permanent magnets into LOAC devices.

When MHD-based microfluidics is equivalent to pressure-driven flow

“…When the device is subjected to an external magnetic field provided by either permanent magnets or electromagnets, the electric current interacts with the magnetic field to produce Lorentz body forces, which, in turn, drive fluid motion. This phenomenon is commonly referred to as magneto-hydrodynamics and has been utilized, among other things, to pump fluids in microfluidic conduits (Qian and Bau 2005; Jang and Lee 2000; Lemoff and Lee 2000; Leventis and Gao 2001;West et al 2002 and2003;Zhong et al 2002;Eijkel et al 2003;Harrison 2003a and2003b;Arumugam et al 2005 and2006;Aguilar et al 2006;Nguyen and Kassegne 2008), control fluid flow in microfluidic networks without a need for mechanical pumps and valves (Bau et al 2003); stir and mix fluids (Bau et al 2001;Yi et al 2002;Xiang and Bau 2003;Qian and Bau 2005;Gleeson and West 2002;West et al 2003;Gleeson et al 2004); and enhance mass transfer next to electrodes' surfaces (Boum and Alemany 1999;Lioubashevski et al 2004;Alemany and Chopart 2007). For a recent review of a few applications of MHD in microfluidics, see Qian and Bau (2009)…”

Modeling RedOx-based magnetohydrodynamics in three-dimensional microfluidic channels

“…The introduction of RedOx species into the liquid is a potential solution to the problems associated with the DC MHD microfluidics. [20][21][22][23][24][25][26] RedOx-based DC MHD has several benefits. For example, the electric potential applied across the electrodes can be very low ͑several mV to ϳ1 V͒, which eliminates the bubble generation problem.…”

Redox magnetohydrodynamic enhancement of stripping voltammetry: toward portable analysis using disposable electrodes, permanent magnets, and small volumes

“…2 Sintered NdFeB magnets are some of the strongest permanent magnets that are commercially available. 23 NdFeB magnetic materials have previously been used with MHD for purposes such as inducing convection in nitrobenzene solution, 24 demonstrating a flow delivery system, 25 and pumping liquids through a ceramic loop. 26 To minimize the volume of the analysis solution required and the heavy metal waste produced, small volume (y150 mL) analyses were performed.…”