Molecular Dynamics Simulation Of Mechanical And Damping Properties Of SU-8 Photoresist And Its Composites

In the recent years, more and more researches focus on the polymer. Many domestic and foreign scholars dedicate themselves to the development of new materials, the synthesis of natural and biomimetic materials with the excellent properties. As SU-8 photoresist is widely used in the field of MEMS, this paper focuses on the study of its mechanical, thermodynamics and damping properties through the methods of molecular dynamics. It can not only predict the macroscopic properties of materials, but also be beneficial for understanding and analyzing microscopic mechanism of materials about the macroscopic phenomenon.Firstly, according to basic theory of molecular mechanics and molecular dynamics, we presented the appropriate methods of the force field, ensemble and boundary conditions. Based on the Compass molecular field, non-crosslinking and crosslinking SU-8 photoresist models were built with the progress of molecule polymerization, energy optimization and anneal simulation. Mechanical properties like Young’s modulus and Poisson’s ratio were calculated. Comparisons between the simulation and the experiment results proved the feasibility of establishing model method and molecular dynamics algorithm.Secondly, the composite blending models of SU-8 photoresist and different types of carbon nanotubes were established. The effect on different types of carbon nanotubes on the mechanical properties were presented by the molecular dynamics simulation. The results showed that the Young’s modulus of composite materials decreased gradually as the increase of diameter of carbon nanotubes. In addition, double walled carbon nanotubes could improve the mechanical properties of composite, which was better than the single wall carbon nanotubes.Thirdly, molecular dynamic simulation was applied to investigate the glass transition temperature of SU-8 photoresist and its main influencing factors. The results showed that the glass transition temperature of non-crosslinking and crosslinking SU-8 photoresist were 326.7K and 494.8K respectively. Meanwhile, we emphatically discussed the effects of the force field energy and the variety of non-bond energy was confirmed to be one of the main causes of the SU-8 photoresist glass transition. This simulation was helpful for the understanding of micro mechanism of the glass transition process. By the Dynamic Mechanism Analysis (DMA) experiment, we studied the glass transition temperature of SU-8 photoresist processed with different parameters. Finally, we calculated the binding energy, radial distribution function, hydrogen bonding and fractional free volume of SU-8 photoresist and its composite. By calculating the composite’s bonding energy, bonding strength of composite materials was obtained. Through the analysis of the radial distribution function, intra-molecular and inter-molecular interaction could be understood further. The influence factors of damping properties were discussed by calculating free volume and hydrogen of the composite. This simulation provided references for the design of polymer with excellent damping properties.