Multi-material Photocuring And Micro-nano Structuring Based On Free Radical-cation Hybrid Photoresist

In recent years,the advanced manufacturing industry has continuously promoted the development of manufacturing technology in the direction of miniaturization,precision and complexity.Since three-dimensional(3D)printing was proposed,as a manufacturing technology that can produce arbitrary three-dimensional objects,it has received extensive attention from researchers.Various 3D printing methods such as photocuring,material jetting,and material extrusion have been invented one after another.Among them,3D printing technology based on the principle of photocuring has high manufacturing resolution and is widely used in electronic products,metamaterial and tissue engineering.However,most 3D printing technologies based on the principle of photocuring are limited to the printing of single material.Although methods such as sequential manufacturing and microfluidics can already achieve multi-material 3D printing,these methods need to use a variety of photoresists and replace them in the printing process,which will cause positioning error and structural damage.The wavelength control method can use one type of photoresist to achieve the forming of multiple materials,which provides a new direction for multi-material 3D printing technology.In this paper,the use of femtosecond laser wavelength control method for multi-material photocuring three-dimensional forming and micro-nano structure preparation of free radical-cation hybrid photoresist is studied.The main work content is shown as follows:(1)The time-dependent density functional theory was used to calculate the ultraviolet absorption spectrum of the photoinitiator.The effects of different basis sets and excited states on the calculation accuracy and time-consuming were studied.According to the calculation results,two photoinitiators,phenyl bis(2,4,6-trimethylbenzoyl)phosphine oxide(Irg 819)and triarylsulfonium hexafluoroantimonate mixture(TAS),were selected and their UV absorption spectra were measured.The results show that the excitation cut-off wavelength of Irg 819 photoinitiator is around 450 nm,and the excitation cut-off wavelength of TAS photoinitiator is around 390 nm.In the range of 390?450 nm,Irg 819 photoinitiator can be selectively excited separately.(2)Irg 819 photoinitiator and TAS photoinitiator were combined with free radical monomers,oligomers and cationic monomers to prepare photoresists.Raman spectroscopy was used to study the polymerization mechanism of these photoresists at different wavelengths.It was found that both cationic polymerization and free radical polymerization could occur when photocuring with 365 nm light-emitting diode(LED)light to obtain the hybrid polymer material of free radical-cationic,and only free radical polymerization occurs when photocuring with 420 nm LED light to obtain free radical polymer material.In order to adjust the properties of the materials obtained after photocuring,the effects of cationic monomer,free radical monomer and photoinitiator on the mechanical properties,gel rate and swelling density of the materials formed by photocuring using 365 nm and 420 nm LED light were studied.(3)Femtosecond laser two-photon polymerization forming system was used to form the free radical and cationic hybrid photoresist.Raman spectra show that free radical and cationic hybrid polymer material can be obtained by using 690 nm femtosecond laser curing,while only free radical polymer material can be obtained by using 780 nm femtosecond laser curing,which realizes laser band selective multi-material laser 3D micro-nano printing.Furthermore,adding SU-8 epoxy resin which can participate in cationic polymerization can increase the viscosity of photoresist and control the diffusion of cation,thus improving the photocuring forming effect.The two-photon fluorescence imaging,swelling ratio measurement,scanning electron microscopy and micro-nano mechanical tester were used to systematically characterize the fluorescence absorption,swelling degree,interface bonding properties and mechanical properties of the multi-material structures.In this work,a variety of materials with different chemical and mechanical properties can be formed in a photoresist with high accuracy,which provides a new solution for the problem of multi-material high-accuracy 3D printing,and can be applied in the fields of micro mechanism,micro framework and tissue engineering.