Study On Shrinkage Characteristics And Compensation Method Of Mechanical Metamaterials In Two-Photon Polymerization

Mechanical metamaterials are composites formed by artificial structures,which have unusual properties not possessed by natural materials,and can realize some strange functions or new functional devices with superior performance than similar functional devices.It is widely used in aerospace,biological scaffolds,microelectronics,optics,acoustics,electromagnetics and other fields.The commonly used mechanical metamaterial processing methods are two-photon polymerization technology,direct laser sintering technology,melt electrospinning technology,nano-imprint printing technology,etc.Among them,two-photon polymerization processing is one of the most potential technologies for processing mechanical metamaterials because of its ability to process arbitrary high-resolution complex three-dimensional micro-nano structures.However,in the process of two-photon polymerization,the cross-linking solidification of photosensitive materials is involved,which leads to the shrinkage of the processed structure,resulting in the reduction of the accuracy or even the loss of the functionality of the three-dimensional micro-nano structure.However,there are few researches on the structure shrinkage and compensation in the process of two-photon polymerization.Therefore,it is of great significance to study the shrinkage characteristics and compensation methods in the process of two-photon polymerization.In this paper,the following research has been carried out on mechanical metamaterial two-photon polymerization processing and shrinkage compensation.(1)Based on the classical Newton mechanics principle and Ormocer photoresist monomer synthesis steps,a random multi-molecular modeling method is proposed to establish the molecular model of photoresist,which makes the established model more in line with the actual photoresist structure.Through molecular dynamics simulation of photoresist crosslinking,the detailed energy changes of the structure in the crosslinking process and the size changes of the package structure before and after polymerization are analyzed,and the shrinkage phenomenon caused by crosslinking reaction in the two-photon polymerization process is proved.Through dynamic analysis of the polymerized photoresist model and the glass substrate,it is revealed that the interaction between the photoresist and the glass substrate is composed of 81.55% Van der Waals force and 18.45% electrostatic force.(2)According to Maxwell's principle,a mechanical metamaterial with a face-centered cubic structure is designed.Through the comparative analysis of the compression resistance of the face-centered cubic structure and the octahedral truss structure under the same relative density,it is proved that the face-centered cubic structure has stronger compression resistance.Through the analysis of Young's modulus of the core cube structure under different relative densities,the change of the mechanical properties of the metamaterial with the change of density is revealed,which provides a theoretical basis for the design of ultra-light,ultra-strong and ultra-tough surface-core cube metamaterial.In addition,through buckling analysis of hollow face-centered cube structure,it is revealed that the first buckling part of the structure is the joint,which provides reference for optimizing the strength of the structure during structural design.(3)Through the analysis of processing parameters in the two-photon polymerization process,the influence of scanning speed and laser power on processing accuracy is revealed.Through finite element modeling,the shrinkage stress in the curing process of photoresist is analyzed,and the change of stress in the curing process of photoresist is revealed.At the same time,the influence of surface adhesion on the shrinkage of processed structure is analyzed.By comparing the size change of structure before and after crosslinking and curing,a shrinkage compensation model is established.