Switchable Direction of Liquid Transport via an Anisotropic Microarray Surface and Thermal Stimuli

Abstract

Design and construction of special surface microstructures has made many amazing breakthroughs in directional liquid transport. Despite much progress in this field, challenges still remain in on-demand switchable direction transport of liquid in situ and real-time via transforming the arrangement of the surface microstructure and external stimuli. Herein, we demonstrate a strategy to achieve switchable direction transport of liquid via a tunable anisotropic microarray surface, that is, assembling a V-shaped prism microarray (VPM) surface, which can also be intelligently manipulated by thermal stimuli. By transforming the parallel and staggered prism microstructure arrangement of the VPM, switchable direction transport of a liquid can be successfully achieved on the VPM surface. Flow direction switching among unidirectional transport, bidirectional transport, and reverse unidirectional transport is also achieved on the temperature-adaptive VPM surface by thermal stimuli, which can be used for on-demand liquid transport according to the paths of the microfluidic channels. The work provides a way for precise liquid manipulation in desired liquid transport, which may be utilized in nonpower conveying systems, autolubrication, life fluid medical instruments, and other microfluidic devices.

Pancake Jumping of Sessile Droplets

“…Coalescence‐induced droplet jumping occurs on superhydrophobic surfaces caused by the release of surface energy during the condensation process, [ 22 , 23 , 24 , 25 , 26 ] but it is limited by the low energy transfer efficiency and thus suffers from a small jumping velocity. [ 27 , 28 ] The directional movement of sessile droplets can be achieved on responsive surfaces through constructing energy gradient, or resorting to stimuli such as temperature, [ 29 , 31 ] pressure, [ 32 , 33 , 34 , 35 ] optical, [ 36 , 37 ] electrical [ 38 , 39 ] or magnetic fields, [ 40 , 41 , 42 , 43 , 44 , 45 , 46 ] etc. In particular, owing to its advantages of instantaneous response, [ 42 ] low energy consumption, flexible/convenient/safe controllability, and good biocompatibility, magnetic actuation has emerged as a promising approach to manipulate droplet motion.…”

Stretch-Enhanced Anisotropic Wetting on Transparent Elastomer Film for Controlled Liquid Transport

“…As reported in the previous work, the interspace of the VPM structure has a great influence on the anisotropic wetting trend on the VPM array surface. 11 Following, the effect of an asymmetric structure of the arranged VPM surface, i.e., radial VPM array structure, on directional water wetting behavior is investigated on a 20 mm × 10 mm silicon surface (Figure S1). Water wetting to the −X direction increases with increasing lateral spacing (a) of the AB end from 20 to 50 μm and fixed lateral spacing (a′) of the CD end on the lubricating oil infused VPM silicon surface.…”

“…As a result, the wetting direction of the droplet on the VPM surface in air is opposite to that on the lubricating oil infused VPM elastomer film, and the droplets slide much more easily on the lubricating oil infused VPM elastomer film. 11 When water droplet is placed on the lubricating oil infused VPM elastomer film, a minor rear curvature radius, and a large front curvature radius is formed between the margins of VPMs in the initial stage. According to the Young−Laplace equation, 11 the additional hydrostatic pressure (ΔP) can be expressed as,…”

Smart Bionic Surfaces with Switchable Wettability and Applications

“…Zhang et al fabricated a temperature-adaptive V-shaped Prism Microstructures (VPM) surface to realize on-demand switchable direction transport of liquid in situ and real-time upon microarrays and thermal stimuli, which was unidirectional, bidirectional and directionally switchable transportation, so as to achieve precise liquid transport according to the path of the microfluidic channel (Fig. 12c) [149] . Inspired by the lotus and pitcher plants, Li and his teamwork fabricated a PDMS@Fe 3 O 4 fabric surface via one-pot method, realizing a switchable surface between the superhydrophobic state and slippery state under external magnetic field, which can achieve anisotropic water transmission and programmable fog harvesting [150] .…”

“…12 (a) Schematic diagram of patterned droplets' release with photomask and droplet array of hidden 2D code information [147] . (b) On-demand directional liquid transport in microfluidic channels [149] . glycans, proteins, etc.…”