PNNL

Abstract

As the characteristic dimension of fluid flow is reduced to the micrometer range, surface energy becomes an increasingly important factor in determining the flow behavior. Because the surface-to-volume ratio is inversely proportional to the width of a channel, forces that arise from surface tension will become comparable to the inertial force of the fluid at a sufficiently small length scale. At this point, it becomes possible to manipulate the motion of the fluid or fluid droplet by modulating the surface tension, which can be achieved with anumberof strategies, including the use of light,1,2 temperature gradients,3,4 electric field,5-7 electrochemical methods,8 and direct patterned surface modifications.9-11 For microfabricated systems, the use of electric field to control dynamically the wetting properties of the surface provides a particularly versatile and convenient approach.12-15 By burying metal electrodes underneath selected dielectric materials,16-18 a circuit can be devised easily and rapidly for manipulating fluid droplet movement using this electrowetting effect.