Droplet Mechanical Hand Based on Anisotropic Water Adhesion of Hydrophobic–Superhydrophobic Patterned Surfaces

Abstract

Superhydrophobic copper surfaces patterned with non-round hydrophobic areas were fabricated by a combination of through-mask chemical oxidation and fluorocarbon film deposition techniques. The anisotropic sliding resistance of droplets on typical non-round hydrophobic patterns such as semicircle, V-shape, and line segment hydrophobic patterns was observed. The dependence of sliding anisotropy on the pattern shape and dimensions was investigated. Results showed that the experimental sliding resistance was in good agreement with the calculated data using a classical drag–resistance model (Furmidge equation). By taking advantage of the anisotropic sliding resistance, these patterned surfaces can be used as droplet mechanical hands to capture, transfer, mix, and release in situ micro droplets by simply moving the surfaces in different directions. A droplet pinned on a non-round hydrophobic pattern can be captured by lifting a surface with another non-round hydrophobic pattern in a large-sliding-resistance direction after touching it, while the captured droplet can be released in situ with nearly no mass loss by horizontally moving the surface in the low-sliding-resistance direction. The lossless droplet manipulations using hydrophobic/superhydrophobic patterned surfaces have advantages of being low in cost and easy to operate and may have great promising applications to high throughput drug screening, molecular detection, and other lab-on-chip devices.

Magnetism-Actuated Superhydrophobic Flexible Microclaw: From Spatial Microdroplet Maneuvering to Cross-Species Control

“…Different from the recently reported water droplet manipulation relying on anisotropic adhesion between water and hydrophobic−superhydrophobic patterned surfaces or liquid-infused surfaces, our flexible microclaw exhibits not only excellent lossless droplet transport but also cross-species sample control. 29,30 Accordingly, collecting debris via droplets was further demonstrated (Figure 5b). The solid debris was collected and transported sequentially by the interfacial adhesion between the paper scraps and a 17 μL droplet clamped by a typical MSFM beforehand (Movie S3).…”

Saturated Surface Charging on Micro/Nanoporous Polytetrafluoroethylene for Droplet Manipulation

“…13,14 Nevertheless, on these patterned surfaces, the liquid residual is likely detained on the superhydrophilic traces and may cause cross-contamination. 14 To avoid the contamination of surfaces, a variety of hydrophobic patterns were created to manipulate droplets without mass loss; 15,16 however, anisotropic sliding resistance is limited on hydrophobic patterns, and it hindered complex droplet motion control.…”

“…Superhydrophobic surfaces with a water contact angle (WCA) that is higher than 150° are considered to be an ideal candidate for manipulating the bead-like droplets. However, on homogeneous superhydrophobic surfaces, only isotropic rolling off and pinning of droplets across the whole surface were feasible. , Precise control of droplet motion was achieved by developing surface patterns with contrast wettability, such as (super) hydrophilic patterns/traces on a superhydrophobic substrate. − These patterned surfaces are usually used for guiding liquid droplets with the aid of gravity and anisotropic sliding resistance, which is induced by the high surface tension of the liquid and low interfacial sliding viscous force on the pattern. ,− The superhydrophilic patterns can also regulate the droplet curvature and produce inner Laplace pressure to propel the spontaneous movement of liquid or droplet. , Nevertheless, on these patterned surfaces, the liquid residual is likely detained on the superhydrophilic traces and may cause cross-contamination . To avoid the contamination of surfaces, a variety of hydrophobic patterns were created to manipulate droplets without mass loss; , however, anisotropic sliding resistance is limited on hydrophobic patterns, and it hindered complex droplet motion control.…”

Rose Pistil Stigma: Hierarchical Superhydrophobic Surfaces with Hydrophilic Microtips for Microdroplet Manipulation

“…As addressed above, the exploration of new surface-wetting properties of biological microstructures is extremely important for the fabrication of smart wetting surfaces, and it has always been an active research field. , After millions of years of evolution, many plants and animals have derived functional surfaces with unique wetting properties from their surroundings. These biological surfaces have become paradigms for developing diverse biomimetic materials. − Many artificial superhydrophobic surfaces with tunable adhesion to water have been developed for microdroplet manipulation, − such as patterned surfaces, mechano-regulated surfaces, and so on. However, most of them are based on flat substrates and toxic chemicals are needed to achieve superhydrophobic surfaces.…”