Triboelectric ‘electrostatic tweezers’ for manipulating droplets on lubricated slippery surfaces prepared by femtosecond laser processing

Abstract

“Electrostatic tweezer” is a promising tool for droplet manipulation, but it faces many limitations in manipulating droplet on superhydrophobic surfaces. Here, we achieve noncontact and multifunctional droplet manipulation on Nepenthes-inspired lubricated slippery surfaces based on triboelectric electrostatic tweezers (TETs). The TET manipulation of droplets on a slippery surface shows many advantages over the electrostatic droplet manipulation on a superhydrophobic surface. The electrostatic field induces the redistribution of the charges inside the neutral droplet, which makes the triboelectric charged rod drive the droplet to move forward under the electrostatic force. Positively or negatively charged droplets can also be moved by TET based on electrostatic attraction and repulsion. TET enables manipulate droplets under diverse conditions, such as anti-gravity climb, the motion of suspended droplets, corrosive liquids, low-surface-tension liquids (e.g., ethanol with a surface tension of 22.3 mN/m), different droplet volumes (from 100 nL to 0.5 mL), passing through narrow slits, sliding over damaged areas, on various solid substrates, and even droplets in an enclosed system. Various droplet-related applications, such as motion guidance, motion switching, droplet-based microreactions, surface cleaning, surface defogging, liquid sorting, and cell labeling can be easily achieved with TET.

Femtosecond laser ultrafast photothermal exsolution

“…Employing higher power lasers accompanied by further increasing scan speed to m•s −1 can make this technique more efficient and practical for industrial applications, rather than being limited in the lab-scale. From material perspective, black and darkblue ZrO 2 can also be potentially applied as solar absorbers [24,52], pigments and dyes [53], and in decoration, implant dentistry [54], photocatalyst [55] fields; while from technique perspective, the applications of our method is as well compatible with those of fs laser ablation/structuring, patterning, and material synthesis within the scope of optics/photonics [56][57][58][59][60][61], energy [62], photoelectronic [63], flexible electronics [64], wettability [65,66], biomimetic [67], bubble/gas manipulation [68], stimulus-responsive interfaces [69], miniaturized robotics [70], fundamental studies [71][72][73][74], etc.…”

Bioinspired directional structures for inhibiting wetting on super-melt-philic surfaces above 1200 °C

“…Inspired by this natural phenomenon, artificial superhydrophobic surfaces have garnered significant attention due to their widespread practical applications in self-cleaning [5,6], droplet manipulation [7][8][9][10], oil-water separation [11,12], drag reduction [13,14], anti-icing [15,16], etc. Nowadays, it is easy to achieve room-temperature superhydrophobicity by constructing micro/nanostructures and implementing chemical modifications [17][18][19][20][21][22][23]. However, the attainment of similar superrepellent properties for molten droplets in high-temperature air environments (e.g.…”

Portable Triboelectric Electrostatic Tweezer for External Manipulation of Droplets within a Closed Femtosecond Laser-Treated Superhydrophobic System

“…Controllable droplet manipulation plays an indispensable role in various applications, such as microfluidics, , printing technology, , biological detection and analysis, , combinatorial chemistry, , water harvesting, , and heat management. , Due to the risk of contamination associated with contact operation, contactless droplet manipulation has attracted increasing attention in recent years. There are usually two strategies for achieving noncontact transport of droplets. − One is to design geometric, chemical, wetting, or even charge gradient structures on the surface of solid materials. − The droplets on the gradient structures have asymmetric three-phase contact lines or contact angles, which enable the droplets to move along the gradient direction spontaneously under the asymmetric forces (e.g., Laplace force). , However, droplet manipulation based on gradient structures is limited by short transport distances, single and fixed transport directions, and irreversible movement, arising from the foundation of these methods (i.e., the limited gradient range and the fixed gradient direction). , Another idea is to change the morphology or other physical and chemical properties of the substrate supporting the droplet through external stimuli (such as magnetism, light, , and electricity) or to directly apply force to the droplets, − making the droplet follow the stimulus source to move forward. Although stimulus strategies allow droplets to move farther and in a more flexible direction than gradient structures, they often rely on essential surface pretreatment or droplet pretreatment. ,,− Nonetheless, despite extensive progress, these contactless manipulations are usually carried out on open material surfaces, and few methods are capable of manipulating droplets in a confined space from the outside without surface or droplet pretreatment.…”

“…In contrast to the magnetism and light stimuli, which drive droplets indirectly by changing the physical and chemical properties of the operating platform, − an electrostatic field can directly apply electrostatic force to droplets. , In addition, the electric field can easily penetrate the insulating material, so electrostatic forces show great potential for droplet manipulation in confined environments. However, electrostatic operating systems based on a high-voltage input are unsafe, not easy to carry, and not convenient enough.…”