Simple but Efficient Method To Transport Droplets on Arbitrarily Controllable Paths

Abstract

The flexible manipulation of droplets manifests a wide spectrum of applications, such as micro-flow control, drug-targeted therapy, and microelectromechanical system heat dissipation. How to realize the efficient control of droplets has become a problem of concern. In this paper, a simple method that can realize the transport of droplets along any controllable path is proposed. It not only has a simple preparation process and clear transport mechanism but is also easy to realize in manipulation technology. A magnetic-sensitive surface is prepared by filling a polymer matrix with magnetic particles and immersing in a lubricant. Under the action of an external magnetic field, rough microstructures are generated locally on the surface, forming the wettability gradient with the area far away from the field. Moving the magnetic field, the wettability gradient region moves accordingly and drives droplets to transport. To better control the transport path of droplets or realize a more complex path design, a ring-shaped magnetic field is further adopted, during which the droplet is automatically located in the ring-shaped region and moves with the movement of the ring-shaped magnetic field. The present technique is simple and easy to implement, which should be helpful in the field of precise regulation of the droplet position.

Target slinging of droplets with a flexible cantilever

“…Considerable attention has recently been drawn to realizing the directional bounce of impacting droplets on solid surfaces. For instance, preferential bouncing induced by artificial surfaces with structural, 12–15 chemical, 16–19 thermal, 20 or charge gradients 21,22 can transport information, materials, and energy, which is successfully applied in many agricultural and industrial fields 23–26 . Despite the extensive progress made by in‐depth studies about the droplet hitting rigid substrate, 27 an actual working substrate in nature is more complicated.…”

“…For instance, preferential bouncing induced by artificial surfaces with structural, [12][13][14][15] chemical, [16][17][18][19] thermal, 20 or charge gradients 21,22 can transport information, materials, and energy, which is successfully applied in many agricultural and industrial fields. [23][24][25][26] Despite the extensive progress made by in-depth studies about the droplet hitting rigid substrate, 27 an actual working substrate in nature is more complicated. Most natural plant leaves, as well as insect wings, are elastic and single-end fixed, which can be simplified as flexible cantilevers.…”

Shaping Liquid Droplets on an Active Air–Ferrofluid Interface

“…Liquid metal droplets can also be moved or stretched to a cross-shaped pattern using magnetic fields when mixed with iron nanoparticles . Droplets can be also transported on magnetic-sensitive surfaces by altering the wettability of the surface using a ring-shaped magnet . Those works have achieved impressive results; however, they have little applicability to the shaping of liquid on the air–liquid interface.…”

“… 22 Droplets can be also transported on magnetic-sensitive surfaces by altering the wettability of the surface using a ring-shaped magnet. 23 Those works have achieved impressive results; however, they have little applicability to the shaping of liquid on the air–liquid interface.…”

Locust-Inspired Direction-Dependent Transport Based on a Magnetic-Responsive Asymmetric-Microplate-Arrayed Surface

“…Micro/nanostructured surfaces with asymmetric properties exhibit high potential applications in the field of biomedicine, diagnostics and therapeutics, and drug development or delivery. − Natural creatures provide many ideas in efficient directional transport on micro/nanostructured surfaces − from which it can be found that efficient asymmetric transport function is always related to the gradient property in surface energy, Laplace pressure, or swing of micro/nanocilia. ,, For example, water can be transported directionally on the peristome surface of Nepenthes alata and the spider silk . The cilia on the respiratory epidermis of mammals can transport the sputum out of the airway, and motile cilia lining the inner walls of the fallopian tubes can transport egg cells to the uterus .…”