Transporting droplets through surface anisotropy

Hal R Holmes,Karl F Böhringer

doi:10.1038/micronano.2015.22

Hal R Holmes, Karl F Böhringer

Open Access

https://doi.org/10.1038/micronano.2015.22

Copy DOI

Abstract

AbstractThis review article examines digital microfluidic systems that manipulate droplets through surface anisotropy. These systems are categorized as surface tension driven or contact line driven. Surface tension driven systems include electrowetting on dielectric, Marangoni flow on microheater arrays, and chemical gradient surfaces, whereas contact line driven systems include anisotropic ratchet conveyors, nanostructured Parylene ratchets, and tilted pillar arrays. This article describes the operating principles and outlines the fabrication procedures for each system. We also present new equations that unify several previous models of contact line driven systems. The strengths and weaknesses of each system are compared, with a focus on their ability to perform the generation, switching, fusion, and fission of droplets. Finally, we discuss current and potential future applications of these systems.

Highlights

Droplet microfluidics is an interdisciplinary field focused on the transport of fluids in small discrete volumes rather than through continuous flow
The segmented flow of droplet microfluidics significantly reduces the volume and reactant quantity requirements compared to continuous flow systems, and it circumvents the issues of Taylor dispersion, solute–surface interactions and cross-contamination[4,5,6,7]
Current digital microfluidics” (DMF) systems operate with larger droplets at lower transport rates[6,7], these systems have the potential to meet a broad range of applications and fulfill a unique niche in the field of microfluidics

Summary

Introduction

Droplet microfluidics is an interdisciplinary field focused on the transport of fluids in small discrete volumes rather than through continuous flow. Contact line driven DMFs When vertical vibrations are applied to a droplet resting on a substrate, axisymmetric waves will form along the surface of the droplet[32]. Unlike surface tension driven DMFs, these systems move droplets through an imbalance of pinning forces on the edges of the contact line. If we instead look at the ratio (Ftrail/Flead) of these opposing forces, we obtain Equation (7), which shows the four components that account for the anisotropy in ARC systems: the two contact angles θ1 and θ2 and the line fractions χlead and χtrail on each edge of the droplet.

Results

Conclusion