Dielectric charge injection (DCI)-enabled contactless droplet wetting modulation for droplet-surface material interchange

Abstract

HypothesisElectrowetting-on-dielectric (EWOD) employs direct droplet-electrode contact to generate electric fields across the dielectric layer to modulate droplet wetting. Because the charged surface state drives this process, it should be possible to accomplish a contactless modulation of droplet wetting by charge injection onto the dielectric surface where a droplet is situated. ExperimentsWe present our technique, dielectric charge injection (DCI), to contactlessly modulate droplet wetting via corona discharge-based physics. We study the ability of droplets on nonwetting surfaces to transition to a wetting state under DCI, quantify contact angle (CA) in relation to applied voltage, and examine reversibility under regimes with and without charge injection. The observed phenomena are applied to enable droplet-surface material interchange. FindingsUsing DCI, we induce wetting of a deionized water droplet on a non-wetting polydimethylsiloxane (PDMS) surface immersed in hexadecane, with tunable CA modulation based on applied voltage. Upon simple removal of the voltage and/or conductor, droplet fully recovers the initial non-wetting state. We combine these capabilities to enable droplet-surface material interchange of two modes: material deposition (droplet-to-surface) and material recovery (surface-to-droplet). DCI presents a unique strategy for contactless, reversible wetting state modulation that is simple yet powerful for applications such as integrating droplet microfluidics to mass spectrometry.