Contactless Transport and Mixing of Liquids on Self-Sustained Sublimating Coatings

TL;DR

This paper introduces a contactless method for transporting and mixing liquids using a sublimating CO2 coating, enabling minimal contact handling of various liquids with potential applications in microfluidics.

Contribution

The study demonstrates a novel sublimation-based technique for contactless liquid handling, expanding capabilities for manipulating diverse liquids without chemical coatings.

Findings

Effective levitation of viscous and low surface tension liquids.

Sublimation enables mixing and coalescence of droplets.

Technique works with colloidal suspensions and non-Newtonian fluids.

Abstract

The controlled handling of liquids and colloidal suspensions as they interact with surfaces, targeting a broad palette of related functionalities, is of great importance in science, technology, and nature. When small liquid volumes need to be processed in microfluidic devices, contamination on the solid-liquid interface and loss of liquid due to adhesion on the transport channels are two very common problems that can significantly alter the process outcome, e.g. the chemical reaction efficiency, or the purity and the final concentrations of a suspension. It is therefore no surprise that both levitation and minimal contact transport methods including non wetting surfaces have been developed to minimize the interactions between liquids and surfaces. Here we demonstrate contactless surface levitation and transport of liquid drops, realized by harnessing and sustaining the natural sublimation of a solid carbon dioxide-coated substrate to generate a continuous supporting vapor layer. The capability and limitations of this technique in handling liquids of extreme surface tension and kinematic viscosity values are investigated both experimentally and theoretically. The sublimating coating is capable of repelling many viscous and low surface tension liquids, colloidal suspensions, and non-Newtonian fluids as well, displaying outstanding omniphobic properties. Finally, we demonstrate how sublimation can be used for liquid transport, mixing and drop coalescence, with a sublimating layer coated on an underlying substrate with prefabricated channels, conferring omniphobicity with a simple physical approach, rather than a chemical one.