Force driven separation of drops by deterministic lateral displacement

We investigate the separation of drops in force-driven deterministic lateral displacement (f-DLD), a promising high-throughput continuous separation method in microfluidics. We perform scaled-up macroscopic experiments in which drops settle through a square array of cylindrical obstacles. These experiments demonstrate the separation capabilities-and provide insight for the design-of f-DLD for drops of multiple sizes, including drops that are larger than the gaps between cylinders and exhibit substantial deformation as they move through the array. We show that for any orientation of the driving force relative to the array of obstacles, the trajectories of the drops follow selected locking directions in the lattice. We also found that a simple collision model accurately describes the average migration angles of the drops for the entire range of sizes investigated here, and for all forcing directions. In addition, we found a difference of approximately 20 degrees between the critical angles at which the smallest and largest drops first move across a line of obstacles (column) in the array, a promising result in terms of potential size resolution of this method. Finally, we demonstrate that a single line of cylindrical obstacles rotated with respect to the driving force is capable of performing binary separations. The critical angles obtained in such single line experiments, moreover, agree with those obtained using the full array, thus validating the assumption in which the trajectory (and average migration angle) of the drops is calculated from individual obstacle-drop collisions.