| Gradient directional wetting of microfluidic surfaces enables complex fluid control,manipulation,and detection at microscopic scales,and has important application prospects in the fields of environment,energy,agriculture,and biomedicine.How to realize the regulation of specific wettability such as superhydrophilic/hydrophobic,anisotropic and directional wetting on the gradient oriented wetting microfluidic surface depends on whether we can design innovative structures in line with microfluidic dynamics and realize the preparation of large-area and high-precision three-dimensional structures.In this paper,a gradient directional wetting model was established by using COMSOL Multiphysics software,and the driving effect of the gradient directional wetting surface on droplets was numerically simulated.According to the special wettability of the inner wall of the sliding area of Nepenthes and the skin of Collembola,the crescent structure and umbrella structure were designed,and the optimized two-photon polymerization processing method was proposed to prepare the wettability array surface with large area and high resolution and the gradient oriented wetting microfluidic surface.This paper mainly carried out the following research:(1)Using COMSOL Multiphysics software,the motion state of droplets on gradient wetted surfaces was simulated and analyzed under the multi-physical field coupling of laminar flow,two-phase flow and level set.The morphology and dynamic variation of droplet on hydrophilic-hydrophilic,hydrophobic-hydrophobic,hydrophobic-hydrophilic gradient surfaces were studied.The influence of wetting gradient on droplet displacement and velocity was revealed,and the hydrodynamic model of gradient driving droplet movement was established.The effectiveness of increasing wetting gradient on improving droplet directional transport efficiency was verified.(2)According to the wetting characteristics of the inner wall microstructure in the slip zone of Nepenthes,the surface of the bionic crescent array of Nepenthes was designed and processed by femtosecond laser two-photon polymerization technology.Aiming at the problems of photoresist convergence and large positioning errors on the substrate surface in the large-area fabrication of two-photon polymerization,the Subregion outside-in scanning method was proposed,and the surface of the bionic crescent array of Nepenthes was successfully realized.Processing across scales.The effects of crescent area fraction,height,offset distance and the ratio of outer and inner arc radius on droplet wettability were explored.By continuously injecting water into the droplets,the phenomenon of droplet spreading in the convex direction and the pinning phenomenon in the concave direction of the crescent were found,and the directional water delivery of the droplets on the surface of the Nepenthes bionic crescent array was realized.(3)According to the super-lyophobic properties of the true three-dimensional surface functional structure on the skin of Collembola,the influence of umbrella-like functional structure parameters on the contact angle of droplets was studied based on the liquid edge effect,and a hydrophobic-hydrophilic bionic umbrella was designed and constructed.The microfluidic surface was directionally wetted by a gradient-like array and processed by femtosecond laser two-photon polymerization.Aiming at the structural deformation problem caused by the drift of the separated structure in the micro-nano additive manufacturing,the dendritic step-by-step two-photon polymerization manufacturing method was proposed,which realized the high-precision manufacturing of the umbrella structure and the wettability of umbrella shaped functional structure was tested.The influence of center distance,lid radius and re-entrant structures on droplet contact angle of umbrella structure was studied,and it was verified that the re-entrant structures played a key role in the regulation of the droplet contact angle. |
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