Analytical solution for transient electroosmotic flow in a rotating microchannel

An analytical solution is developed for the unsteady flow of fluid through a parallel rotating plate microchannel, under the influence of electrokinetic force using the Debye–Hückel (DH) approximation.

Electrowetting on Dielectric (EWOD) Assisted Droplet Desiccation

Lab-on-a-chip (LOAC) devices are emerging technologies that aim to perform all of the laboratory functions of traditional diagnostic tests on single microchips. Microarrays are one promising type of LOAC device that consist of an array of droplets for testing tens to thousands of samples simultaneously. Microarrays are commonly used in gene sequencing, pathogen detection, determining microbial resistances, and conducting enzyme-linked immunosorbent assays (ELISAs). As droplets in these arrays dry, the majority of material within the droplet is deposited around the periphery. This phenomenon is referred to as the coffee stain effect. The non-uniform depositions left by this effect can result in variation of fluorescence intensity measurements in automated vision systems. A means of producing more uniform particle depositions for the microscopy analysis would allow for more accurate test results. One promising method for suppression of the coffee stain effect involves the use of electrowetting on dielectric (EWOD). EWOD devices apply an electrokinetic force at the three-phase contact line to manipulate the shape of a droplet interface. The Mugele group has already begun investigating EWOD’s effects on the coffee stain effect and found that an AC voltage applied to droplets on EWOD devices can suppress the coffee stain effect and produce smaller, more uniform droplet deposition patterns. This work presents (i) a method to characterize the deposition pattern left by a desiccated droplet as a function of radial position and (ii) a discussion of the microfabrication technique used to create devices to perform EWOD assisted desiccation for both AC and DC voltages.

A Generalized Analysis of Electroosmotically Driven Capillary Flow in Rectangular Microchannels

In this study, the transient response of the fluid with combined electrokinetic and capillary effect in a microchannel is investigated theoretically. A second-order differential governing equation is obtained which represent the electroosmotic and capillary flow in a rectangular microchannel. This governing equation takes care of inertial force, dynamic contact angle, electrokinetic and entrance effect. The electrokinetic effect is modeled through additional electrokinetic force, which varies along the penetration depth of fluid. The non-dimensional analysis is presented by normalizing the gravity, viscous, electrokinetic forces with surface tension force. New non-dimensional group for electrokinetic force is reported which represents the ratio of electrokinetic and surface tension forces. The numerical solution of the governing equation is validated with experimental and analytical results for capillary flows, which shows good agreement. It is observed that for smaller Eo the capillary front advancement follows the similar trend as pure capillary flow but for higher Eo, the electroosmotic force dominates over surface tension force. It is demonstrated that this model provides simple approach to predict the penetration depth in electroosmotically driven capillary flow.

Effects of Surface Texturing on Lubrication Theory: Consideration of Electrodouble Layer (EDL)

The effects of surface texturing on the electrohydro-dynamic lubrication with thin double layers are considered for the sliding of one charged body past another in an electrolyte solution. The averaged Reynolds type equation as well as the related flow factors is then derived by the flow factor method. The couple effects of surface roughness and EDL appear on flow factors are discussed. The hydrodynamic pressure generated by the viscous force and electrokinetic force are discussed for an 1-D slider bearing.

Manipulation of Bio-Particles by Electrokinetics

We propose and develop a new bio-particles manipulation device that has the similar size order as targeted bio-objects and is a non-contact approach to bio-objects using AC electrokinetics. We use micro pyramid array made by MEMS KOH anisotropic etch in our design. Simulation results using CFD-ACE+ and ANSYS show extremely high electric field around micro pyramids for our concept proof. Experimental results successfully demonstrate the feature of micro-object manipulation for our device. In this paper, we will present the design, fabrication, modeling, simulation, and testing results of our manipulation device using electrokinetic force.