Modeling the trajectory of microparticles subjected to dielectrophoresis in a microfluidic device for field flow fractionation Bobby Mathew a , Anas Alazzam a,n , Mohammad Abutayeh a , Amjad Gawanmeh b , Saud Khashan c a Department of Mechanical Engineering, Khalifa University, Abu Dhabi, UAE b Computer and Software Engineering, Khalifa University, Sharjah, UAE c Department of Mechanical Engineering, UAE University, Al Ain, UAE HIGHLIGHTS  Trajectory of microparticles subjected to dielectrophoresis is modeled.  Model accounts for forces due to inertia, gravity, buoyancy, virtual mass and dielectrophoresis.  Steady state levitation of microparticle is dependent on voltage and electrode/gap length.  Steady state levitation of microparticle is independent of microparticle radius, microchannel height and flow rate.  Levitation, under transient conditions, is influenced by all operating and geometric parameters. article info Article history: Received 28 December 2014 Received in revised form 10 June 2015 Accepted 5 July 2015 Available online 30 July 2015 Keywords: Dielectrophoresis (DEP) Field flow fractionation (FFF) Interdigitated transducer electrodes Microparticles Trajectory Microchannel abstract This article details the development of an experimentally validated model for tracking the movement of microparticles in a continuous flow microfluidic device employing dielectrophoresis for purposes of field-flow fractionation. This device employs interdigitated transducer electrodes on the bottom surface of the microchannel. The electric potential inside the microchannel is defined by Laplace equation while the trajectory of the microparticles is described by governing equations based on Newton’s second law. Forces due to inertia, gravity, buoyancy, dielectrophoresis and virtual mass are accounted for in this model. The governing equations are solved using finite difference method. The model is subsequently used for parametric study; the parameters analyzed include microparticle radius, applied voltage, volumetric flow rate, microchannel height and electrode/gap length. As per the model the levitation height, under steady state conditions, of the microparticles is independent of the microparticle radius, volumetric flow rate and microchannel height, it is dependent on the applied voltage and electrode/gap length. The levitation height, under transient conditions, is dependent on all these parameters. & 2015 Elsevier Ltd. All rights reserved. 1. Introduction Dielectrophoresis (DEP) is the phenomenon in which neutral but polarizable microparticles, dispersed in a medium, transverse when subjected to a non-uniform electric field (Çetin and Li, 2011; Sajeesh and Sen, 2013; Sant and Gale, 2007). The microparticles transverse towards either the field maxima or minima; the preference of maxima/minima depends on electrical properties, specifically con- ductivity and permittivity, of the microparticles and medium as well as the applied frequency (Çetin and Li, 2011; Sajeesh and Sen, 2013; Sant and Gale, 2007). The influences of these parameters are incorporated into Clausius–Mossotti (CM) factor; when the real part of CM factor is positive and negative the entity will move towards the maxima and minima of the gradient of the magnitude of electric field, respectively. When the microparticles move towards the maxima and minima of a non-uniform electric field then DEP is specifically termed as positive-DEP (pDEP) and negative-DEP (nDEP), respectively (Çetin and Li, 2011; Sajeesh and Sen, 2013; Sant and Gale, 2007). DEP is employed in microfludic devices for purposes such as separation, trapping, capture and sorting of microparticles (Çetin and Li, 2011; Sajeesh and Sen, 2013; Sant and Gale, 2007). Field-flow fractionation (FFF) is a technique for separating micro- particles in a heterogeneous mixture of the same into homogeneous mixtures with similar properties (Reschiglian et al., 2005). In a DEP- FFF microdevice the sample containing microparticles is subjected to a nDEP field, applied normal to the direction of flow, thereby repelling Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/ces Chemical Engineering Science http://dx.doi.org/10.1016/j.ces.2015.07.014 0009-2509/& 2015 Elsevier Ltd. All rights reserved. n Corresponding author. Tel.: þ971 2 501 8460. E-mail address: anas.alazzam@kustar.ac.ae (A. Alazzam). Chemical Engineering Science 138 (2015) 266–280