Direct Laser Writing Of 3D Microstructures And Their Interaction With Liquid

In recent years,with the development of processing technologies,a variety of microstructures have been fabricated so as to control the wettability better.At the same time,based on the wettability-induced capillary force,the deformation of microstructures can also be controlled,and therefore three-dimensional(3D)complex microstructures can be fabricated.Two-photon polymerization based 3D printing(TPP 3D printing)technology(direct laser writing technology)is currently one of the most effective approaches to fabricate various 3D micro complex microstructures that cannot be fabricated by other traditional technologies.However,due to the limitations of voxels,this technology is still unable to directly prepare many complex microstructures.Based on the interaction between liquid and three-dimensional microstructures,re-entrant structures are fabricated by direct laser writing technology to control the repellence and adhesion behavior of fluid phase.Similar microstructures are difficult to fabricate by conventional means.In addition,capillary force is used to control the deformation of 3D microstructures,and more complex microstructures are fabricated and reversible deformation is achieved.The main research contents are as follows:(1)Based on the natural model of the springtail skin,micro multiply re-entrant structures are designed and fabricated by two-photon polymerization based TPP 3D printing technology,which enhance the breakthrough pressure to the liquids.These modification-independent structures are able to suspend almost all liquids at room temperature.In addition,the structures can be prepared on a variety of substrates,including flexible polyimide films,hard silicon wafers,etc.With the help of two parallel walls constructed on the top of the triply re-entrant array,the capillary force is successfully controlled and directional liquid flow is realized.The arrays with triply re-entrant structures fabricated by this technology can be applied in many fields,including waterproof and anti-fouling of electronic devices,optical display,high-throughput biochemical detection,microfluidic transmission and so on.(2)The capillary force of liquid on the multiply re-entrant structures is theoretically analyzed.If the arrangement of the array and the size of each microstructure are carefully designed,high adhesion and high contact angle can be realized simultaneously towards oil and water.These structures that combine the springtail-skin effect and the gecko-feet effect can be used in the transfer of liuid droplet,the generation of microfluidic array and so on.(3)Theriotical and experimental results confim that the repellence for on fluid phase in another insoluble phase can be realized based on the multiply re-entrant structures.In addition,through elaborate design,the cylindrical part of the re-entrant structures can deform when subjected to evaporation-induced capillary force,and such deformation can be restored in some other liquids.Therefore,the reversible transition of repellence and spreading is realized.(4)Asymmetric printing is introduced to the TPP 3D printing technology and directional bending is realized.With the help of the capillary force,a second deformation is observed and 3D complex microstructures can be obtained.Similar to the work in the previous part,the deformed structure can be restored in some other liquids.The capillary-assisted asymmetric TPP 3D printing technology can be applied in directional flow of liquid,tunable liquid repellence,4D printing,etc.