Shuai Zhao

Bio: Shuai Zhao is an academic researcher from Jilin University. The author has contributed to research in topics: Photolithography & Anti-reflective coating. The author has an hindex of 5, co-authored 5 publications receiving 374 citations.

Three-Level Biomimetic Rice-Leaf Surfaces with Controllable Anisotropic Sliding

Abstract: Rice leaves with anisotropic sliding properties have the ability to directionally control the movement of water microdroplets. However, the realization of artifi cial anisotropic sliding biosurfaces has remained challenging. It is found, by a systematic investigation, that the height of 200μ m-width groove arrays on rice leaves reaches up to 45 μ m, far greater than the smaller microgrooves that are widely adopted for the study of anisotropic wetting. A new model based on three-level microstructures (macro/micro/nano) is developed to interpret the anisotropic sliding behavior. Moreover, artifi cial rice leaves with different macrogrooves are demonstrated by combining micro/nanostructures and macrogrooves, which are prepared by photolithography, PDMS imprinting, and micro/nanostructure coating. Sliding-angle measurement further prove that the third-level macrogroove arrays are the determining factor for anisotropic sliding. Finally, a new testing method, curvature-assisted droplet oscillation (CADO), is developed to quantitatively reveal the anisotropic dynamic behavior of biomimetic rice-leaf-like surfaces.

Facile creation of hierarchical PDMS microstructures with extreme underwater superoleophobicity for anti-oil application in microfluidic channels

Abstract: Composition modification and surface microstructures have been widely utilized in interface science to improve the surface performance. In this paper, we observed a significant improvement of oil contact angle (CA) from 66 ± 2° to 120 ± 4° by introducing a radical silanol group on a flat PDMS surface through oxygen plasma pretreatment. By combining surface microstructures and plasma modification, we produced three kinds of superoleophobic surfaces: 20 μm pitch micropillar arrays, 2.5 μm pitch micropillar arrays and gecko foot-like hierarchical microstructures. Among them, the hierarchical surface with high surface roughness showed extreme underwater superoleophobicity, which featured ultrahigh CA (175 ± 3°) and ultrasmall sliding angle (<1°). Quantitative measurements demonstrated that these superoleophobic surfaces exhibited distinct adhesive behaviors, by which they were interpreted as Wenzel's, Cassie's and the Lotus state, respectively. A microfluidic channel with superoleophobic microstructures was further created by novel curve-assisted imprint lithography, and the characterization based on anti-oil contamination applications was carried out and discussed. We believe that the superoleophobic surfaces will power broad applications in oil microdroplet transportation, anti-oil channels and droplet microfluidic systems.

Mechanical stretch for tunable wetting from topological PDMS film

Abstract: In this paper, we report a mechanical stretch method for tunable wetting from elastic topologically grooved poly(dimethysiloxane) films. The mechanical strain was applied to elongate the film along two orthogonal directions, perpendicular and parallel to the grooves. Along with the increase of mechanical strain, the primary anisotropic wetting of the films was turned into isotropic or a larger degree of anisotropy depending on the stretching direction. The roughness factor as well as the energetic barrier are responsible for the wetting tuning. Effects of the height and period on tunable wetting were investigated, and multiple-cycle reversible switching between anisotropic and isotropic many times was achieved.

Rapid, controllable fabrication of regular complex microarchitectures by capillary assembly of micropillars and their application in selectively trapping/releasing microparticles.

Abstract: A simple strategy to realize new controllable 3D microstructures and a novel method to reversibly trapping and releasing microparticles are reported. This technique controls the height, shape, width, and arrangement of pillar arrays and realizes a series of special microstructures from 2-pillar-cell to 12 cell arrays, S-shape, chain-shape and triangle 3-cell arrays by a combined top down/bottom up method: laser interference lithography and capillary force-induced assembly. Due to the inherent features of this method, the whole time is less than 3 min and the fabricated area determined by the size of the laser beam can reach as much as 1 cm 2 , which shows this method is very simple, rapid, and high-throughput. It is further demonstrated that the ‘mechanical hand’-like 4-cell arrays could be used to selectively trap/release microparticles with different sizes, e.g., 1.5, 2, or 3.5 µ m, which are controlled by the period of the microstructures from 2.5 to 4 µ m, and 6 µ m. Finally, the ‘mechanical hand’-like 4-cell arrays are integrated into 100 µ m-width microfl uidic channels prepared by ultraviolet photolithography, which shows that this technique is compatible with conventional microfabrication methods for on-chip applications.

Simultaneous efficiency enhancement and self-cleaning effect of white organic light-emitting devices by flexible antireflective films.

Abstract: In this Letter, we report the improved light outcoupling efficiency of conventional white organic light-emitting devices (OLEDs) by a kind of multifunctional film with both antireflective and superhydrophobic ability. This film consisted of regular polydimethylsiloxane (PDMS) nanopillar arrays, which were readily batch produced by low-cost imprint lithography. The nanopillar arrays could effectively eliminate the light total reflection and enhance the device efficiency of OLEDs by producing the gradual refractive index due to the decreasing material density from glass to air. Moreover, owing to its superhydrophobicity (contact angle ∼151°), the antireflective film exhibited self-cleaning ability, which was beneficial for keeping the OLEDs substrate clean and ensure the high efficiency of OLEDs. This method is simple, cost-effective, and reproducible. The OLEDs showed an efficiency enhancement of 25% with the multifunctional film.

Emerging Droplet Microfluidics

Abstract: Droplet microfluidics generates and manipulates discrete droplets through immiscible multiphase flows inside microchannels Due to its remarkable advantages, droplet microfluidics bears significant value in an extremely wide range of area In this review, we provide a comprehensive and in-depth insight into droplet microfluidics, covering fundamental research from microfluidic chip fabrication and droplet generation to the applications of droplets in bio(chemical) analysis and materials generation The purpose of this review is to convey the fundamentals of droplet microfluidics, a critical analysis on its current status and challenges, and opinions on its future development We believe this review will promote communications among biology, chemistry, physics, and materials science

Hydrophilic directional slippery rough surfaces for water harvesting

Abstract: Multifunctional surfaces that are favorable for both droplet nucleation and removal are highly desirable for water harvesting applications but are rare. Inspired by the unique functions of pitcher plants and rice leaves, we present a hydrophilic directional slippery rough surface (SRS) that is capable of rapidly nucleating and removing water droplets. Our surfaces consist of nanotextured directional microgrooves in which the nanotextures alone are infused with hydrophilic liquid lubricant. We have shown through molecular dynamics simulations that the physical origin of the efficient droplet nucleation is attributed to the hydrophilic surface functional groups, whereas the rapid droplet removal is due to the significantly reduced droplet pinning of the directional surface structures and slippery interface. We have further demonstrated that the SRS, owing to its large surface area, hydrophilic slippery interface, and directional liquid repellency, outperforms conventional liquid-repellent surfaces in water harvesting applications.