C1lc20749k 4221..4227

Laplace barriers composed of full-posts or ridges have been previously reported as a mechanism for virtual fluid confinement, but with unstable displacement (capillary fingering or fluid trapping, respectively). A new platform of ‘partial-posts’ eliminates the disadvantages of full-posts or ridges, while providing 60–80% open channel area for rapid electrowetting fluid transport (>5 cm s ). The fluid mechanics of partial-post Laplace barriers are far more complex than previous Laplace barriers as it involves two mechanisms: fluid can first begin to propagate either between, or under, the partialposts. Careful design of channel and partial-post geometries is required, else one mechanism will dominate over the other. The physics and performance of partial-post Laplace barriers are verified using theoretical equations, experimental results, and dynamic numerical modeling.