Charge Effects and Nanoparticle Pattern Formation in Electrohydrodynamic NanoDrip Printing of Colloids

TL;DR

This paper investigates the physics of NanoDrip electrohydrodynamic printing, focusing on charge transport and nanoparticle distribution, revealing how electric fields and ligand properties influence pattern formation at the nanoscale.

Contribution

It provides new insights into charge localization and nanoparticle behavior during NanoDrip printing using asymmetric electric fields and nanoparticle dispersions.

Findings

Alternating charge droplets can be spatially separated with an AC electric field.

Nanoparticles are the primary charge carriers within droplets.

Ligand length affects nanoparticle mobility after deposition.

Abstract

Advancing open atmosphere printing technologies to produce features in the nanoscale range has important and broad applications ranging from electronics, to photonics, plasmonics and biology. Recently an electrohydrodynamic printing regime has been demonstrated in a rapid dripping mode (termed NanoDrip), where the ejected colloidal droplets from nozzles of diameters of O(1 {\mu}m) can controllably reach sizes an order of magnitude smaller than the nozzle and can generate planar and out-of-plane structures of similar sizes. Despite demonstrated capabilities, our fundamental understanding of important aspects of the physics of NanoDrip printing needs further improvement. Here we address the topics of charge content and transport in NanoDrip printing. We employ quantum dot and gold nanoparticle dispersions in combination with a specially designed, auxiliary, asymmetric electric field, targeting the understanding of charge locality (particles vs. solvent) and particle distribution in the deposits as indicated by the dried nanoparticle patterns (footprints) on the substrate. We show that droplets of alternating charge can be spatially separated when applying an ac field to the nozzle. The nanoparticles within a droplet are distributed asymmetrically under the influence of the auxiliary lateral electric field, indicating that they are the main carriers. We also show that the ligand length of the nanoparticles in the colloid affects their mobility after deposition (in the sessile droplet state).