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

Abstract

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 (drops on the order of microliters or nanoliters) 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, for example, the chemical reaction efficiency or the purity and the final concentration of a suspension. It is, therefore, no surprise that both levitation and minimal contact transport methods-including nonwetting 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 using a simple physical approach (i.e., phase change) rather than a chemical one. The independence of the surface levitation principle from material properties, such as electromagnetic, thermal or optical, surface energy, adhesion, or mechanical properties, renders this method attractive for a wide range of potential applications.

Poloxamer/Poly(ethylene glycol) Self-Healing Hydrogel for High-Precision Freeform Reversible Embedding of Suspended Hydrogel

“…From calculation, a cured silicone surface tension value of 22.6 ± 3.1 mN m −1 (Figure S4) was found, which compares well with those reported in the literature. 37,38 From these values, interfacial tensions (γ sl ) of 16.9 ± 0.6 and 20.8 ± 0.4 mN m −1 were calculated for P407 and PEG400/ P407, respectively. Compared to the value obtained by O'Bryan et al (13.1 ± 2.2 mN m −1 ), 7 these interfacial tensions are expected to degrade the initial 50 μm highresolution capability of the FRESH 3D printing.…”

The partial fire protection of steel members: a comparative study

“…A significant advantage of these coatings is their durability and their resistance to external influences, including mechanical stresses. However, the comparatively high cost of sublimating coatings is problematic (Milionis et al. , 2017).…”

Droplet Self-Propulsion on Superhydrophobic Microtracks

“…D irectional droplet mobility in so-called segmented flows is a desired functionality for a wide range of applications, such as microfluidics, 1,2 on-chip devices, 2 mixing for chemical processes, 3,4 water collection from the atmosphere, 5 and filtration. 6 Traditionally, droplet generation and motion is achieved by using mechanical or electric power, such as in printing and pumping applications.…”

“…Directional droplet mobility in so-called segmented flows is a desired functionality for a wide range of applications, such as microfluidics, , on-chip devices, mixing for chemical processes, , water collection from the atmosphere, and filtration . Traditionally, droplet generation and motion is achieved by using mechanical or electric power, such as in printing and pumping applications. − Other active approaches have also been explored in the past to stimulate droplet motion, such as light, , heat, magnetic, electric, , or acoustic fields, often requiring tailored liquid properties to realize actuation.…”