Unidirectional Self-Driving Liquid Droplet Transport on a Monolayer Graphene-Covered Textured Substrate

Abstract

Controllable directional transport of liquid droplets on a functionalized surface has been a challenge in the field of microfluidics because it does not require energy supply, and the physical mechanism of such self-driving transport exhibits extraordinary contribution to fundamental understanding of some biological processes and the design of microfluidic apparatus. In this paper, we report a novel design of a surface microstructure that can realize unidirectional self-driving liquid mercury (Hg) droplet transport on a graphene-covered copper (Cu) substrate with a three-dimensional surface microstructure. We have demonstrated that a liquid Hg droplet spontaneously propagates on a grooved Cu substrate covered by a monolayer graphene without any external force fields. Classical molecular dynamics results provide a profound insight on the self-driving process of Hg droplets. It shows that the Hg droplet undergoes acceleration, deceleration, and return stages successively from the narrow to wide ends of the gradient groove. Intriguingly, Hg droplets can move continuously and unidirectionally on the three-dimensional graphene-covered surface microstructure when they accumulate enough kinetic energy from the gradient groove to break the energy barrier at the step junctions between the two neighboring unit cells. The design of the zigzag textured surface covered by a monolayer graphene artfully uses the facts; (1) the monolayer graphene can effectively reduce the droplet pinning on the textured surface, (2) the hydrophobic graphene layer reduces the friction between Hg droplets and the substrate, and (3) the textured surface can permeably interact with the droplets through the monolayer graphene to achieve a continuous self-driving process. The findings reported here open a door to explore the graphene-covered functional surface to directional transport of liquid droplets and provide an in-depth understanding of the self-driving mechanism for liquid droplets on graphene-covered textured substrates.

3D Printing Mechanically Robust and Transparent Polyurethane Elastomers for Stretchable Electronic Sensors

“…Direct ink writing (DIW) , and fused deposition modeling (FDM) printing technologies have been used to print elastomers for stretchable sensors. However, the lack of precise micro/nanofluidic systems limits the print resolution and printing speed of DIW and FDM. , The photocuring-based approach can create complex 3D geometries by spatially controlling light to solidify the photocurable resins into 3D objects and is known as the fastest process for high-resolution products. − A digital light processing (DLP) printer projects a mask pattern onto a resin tank and enables an entire layer to be cured at once, resulting in its high printing speed. , …”

Realizing surface amphiphobicity using 3D printing techniques: A critical move towards manufacturing low-cost reentrant geometries

“…Therefore, based on the specific applications relating to self-cleaning [21], anti-fouling [22], anti-icing [23], anti-corrosion [24], drag reduction [25] and many others, superamphiphobicity may be introduced where metals, polymers and ceramics are used as the base substrates [26]. Another key area of application for superamphiphobic surfaces lies in the self-driving, anti-gravity unidirectional transport mechanisms [27,28] especially in the design of microfluidics transportation where pumping liquids using an external source may not be possible. This kind of surface modification plays a vital role in preserving and enhancing long-term utility of materials where surface coating is not an option and the intrinsic properties of base substrate are required [12].…”

Generation of Nanodroplet Reactors and Their Applications in In Situ Controllable Synthesis and Transportation of Ag Nanoparticles

“…[ 10 ] Recently, interest in fabricating microfluidic chips, micromixers, microactuators, and microfluidic transmissions requires developing smaller and more accurate micro‐/nano‐fluidic systems, which urges a deeper understanding of the formation mechanism and manipulation strategy of the nanoscale droplets. [ 11 ] Therefore, seeking new strategies for preparing and manipulating nanodroplets under general conditions and environments is necessary. On the other hand, nanoscale materials would present unique properties from their bulk materials.…”