High‐Performance Unidirectional Manipulation of Microdroplets by Horizontal Vibration on Femtosecond Laser‐Induced Slant Microwall Arrays

Abstract

The high‐performance unidirectional manipulation of microdroplets is crucial for many vital applications including water collection and bioanalysis. Among several actuation methods (e.g., electric, magnetic, light, and thermal actuation), mechanical vibration is pollution‐free and biocompatible. However, it suffers from limited droplet movement mode, small volume range (VMax/VMin < 3), and low transport velocity (≤11.5 mm s−1) because the droplet motion is a sliding state caused by the vertical vibration on the asymmetric hydrophobic microstructures. Here, an alternative strategy is proposed—horizontal vibration for multimode (rolling, bouncing/reverse bouncing, converging/diffusing, climbing, 90o turning, and sequential transport), large‐volume‐range (VMax/VMin ≈ 100), and high‐speed (≈22.86 mm s−1) unidirectional microdroplet manipulation, which is ascribed to the rolling state on superhydrophobic slant microwall arrays (SMWAs) fabricated by the one‐step femtosecond laser oblique ablation. The unidirectional transport mechanism relies on the variance of viscous resistance induced by the difference of contact area between the microdroplet and the slant microwalls. Furthermore, a circular, curved, and “L”‐shaped SMWA is designed and fabricated for droplet motion with particular paths. Finally, sequential transport of large‐volume‐range droplets and chemical mixing microreaction of water‐based droplets are demonstrated on the SMWA, which demonstrates the great potential in the field of microdroplet manipulation.

Magneto‐Responsive Shutter for On‐Demand Droplet Manipulation

“…Dynamical droplet manipulation using responsive structured surfaces has attracted a lot of attentions due to their great potential in water collection, [ 1 , 2 , 3 ] digital microfluidics, [ 4 , 5 ] chemical reaction, [ 6 , 7 ] and biomedical analysis. [ 8 , 9 ] Responsive structured surfaces can reversibly change the surface topography in response to external stimuli (e.g., mechanical forces, [ 10 , 11 , 12 ] electric, [ 5 , 13 ] thermal, [ 14 ] light, [ 8 , 9 , 15 ] and magnetic field). [ 16 ] Among these manipulation strategies, magnetic actuation has the incomparable advantages of biocompatibility, remote control, instantaneous response, and free of specific environmental requirement.…”

Electrostatic tweezer for droplet manipulation

“…Fig. 2C shows that droplets with volumes ranging from tens of nanoliters to several milliliters could be moved by the tweezer, demonstrating a broad volume range up to five orders of magnitude, which is three orders of magnitude higher than that reported in recent work (40). Furthermore, the DEST could also simultaneously manipulate multidroplets in an array because the droplets carry the same polarity of electrostatically induced charges, as shown in the lower part of Fig.…”

Preparation and Hydrophobicity of Bionic Structures Based on Composite Infiltration Model

“…In recent years, scholars all over the world have conducted a large number of experiments and studies on superhydrophobic functional surfaces. There are many preparation methods, including sol-gel method [11], template method [12], chemical vapor deposition [13], laser-processing method [14] and so on. Many micro-nano manufacturing methods have been applied to prepare super-slip surfaces [15][16][17][18], but most of these methods are to build an additional layer of heterogeneous porous structure on the substrate material, and then refill lubricating oil to further obtain super-slip properties.…”