Preparation Of Bionic Structured Functional Surfaces And Research Of Controlled Droplet Transport

Droplet transport has a wide range of applications in healthcare,environmental protection,and energy production,such as digital microfluidic systems,energy harvesting,water harvesting and oil-water separation,which is important to achieve autonomous and easy manipulation of droplets in small device fluid manipulation systems.Fluid manipulation systems can be divided into closed and open systems.Closed microfluidic systems require pumping devices to drive droplet motion due to large fluid resistance,which reduces their flexibility,while open microfluidic systems are expected to solve this problem.The bionic superwetting surface provides a way to achieve controllability for open microfluidics.Over hundreds of millions of years,organisms in nature have evolved the ability to autonomously transport droplets based on surface wettability in order to adapt to natural environment,such as the patterned surfaces of desert beetles,moving cilia and cactus spines.Inspired by nature,humans have developed a series of surfaces with droplet transport capabilities by mimicking the morphological and structural features of biological surfaces,and applied in energy,microfluidics,bioanalysis,and medical devices.However,conventional surfaces are usually complicated to prepare,costly,difficult to produce on a large scale,and the problem of poorly controlled droplet transport still exists,which limits the wide application of surfaces.Structured functional surfaces with droplet directional transport,direction selective transmission,programmable transport,and anti-gravity transport capabilities were designed and prepared using a variety of biological prototypes with simple laser selective processing,magnetic field assisted and chemical etching.And the transport mechanisms of droplets on functional surfaces were investigated.The main conclusions can be summarized as follows:（1）Inspired by desert beetle patterned surface,a biomimetic hybrid wettability surface was designed using laser selective etching,in which the contact angle of the superhydrophobic region reached 153.1°,while the contact angle of the patterned site was close to 0°.Due to the difference in wettability,droplets are transferred from superhydrophobic region to hydrophilic site,and the directional transport of droplets is achieved.Based on the flexibility of bionic surface,it was integrated into a wearable device with instant,multi-metric and semi-quantitative detection capabilities,and the utility of the bionic surface was verified with colorimetric reactions of acid-base solutions,nitrites,amyloplasts and proteins.（2）Inspired by active cilia,a bionic functional surface with cilia structure was prepared by magnetic field assisted and laser selective etching.Micro and nano structures were formed on the cilia surface under laser ablation.The surface was superhydrophobic and low-adhesive due to the air layer.By changing magnetic field direction,the cilia oscillation direction was changed,droplets on the surface were easily transported in the direction of cilia oscillation by cilia propulsion and low adhesion resistance.Direction-selective transfer of droplets was achieved by controlling the direction of cilia through magnets.In addition,the surface had good physical and chemical stability.（3）Based on the previous research,inspired by superhydrophobicity of lotus leaf surface and the hybrid wettability of desert beetle surface,a white substrate magnetically responsive surface was prepared by method of simple scratch coating using PDMS,Si O₂ and Co.The bionic surface containing highly adherent sites and superhydrophobic regions were obtained by laser selective processing.Inclination angle was produced by magnet,and the droplets were precisely manipulated under unbalanced forces,enabling programmable transport and dispersion of single droplet.For droplets smaller than 2μL,initial velocity of droplet transport was achieved by bouncing.The feasibility of bionic patterned surface as a microreaction platform was demonstrated by reactions of acid-base indicators,Cu SO₄ and Fe Cl₃.（4）Based on the previous research on wettability,the bionic wedge-shaped patterned surface was designed and prepared inspired by cactus spines.The droplet has the ability of anti-gravity self-transport on patterned surface,and the driving force comes from the Laplace pressure generated by the structural gradient.Reducing the contact angle of patterned surface and choosing suitable wedge angle are beneficial to the droplet self-transport on the patterned surface.Reducing the droplet volume is conducive to the complete anti-gravity self-transport of droplet.