Molecular Dynamics Simulation Of Polyimide And Numerical Calculation And Optimization Of Film Drying Process

Polyimides(PIs)is one of the most important functional polymers in recent years because of their excellent properties.However,some shortcomings have limited their further applications in various fields.In this dissertation,the functionalized polynorbornene(PNBE)was introduced to design the molecular structure of PIs from molecular level using Materialstudio software.The structure,compatibility,mechanical properties,crystallinity,diffusivity and other properties of PI/PNBE hybrid system were investigated.The PI film was prepared by polyamic acid solution(PAA),and the reaction process of PAA and the effect of temperature and solid content on the evaporation process were studied by investigated by FT-IR and rotational viscometer.Meanwhile,in order to deeply study the drying mechanism,the physical model of drying process was established and solved by discrete method in Visual Basic(VB)language.The effects of coating parameters,including temperature,solid content,and drying time,on the concentration field,diffusion coefficient,volume fraction were investigated.The results showed that the size and density of PI cell were gradually stabilized after energy/geometric and molecular dynamics optimization.The cohesive energy density and solubility parameter were close to the actual value,which proved the rationality of the encapsulation model.Compared with pure PI,the introduction of the crosslinked structure reduced the compatibility of PI/PNBE,but the barrier properties to DMF and water molecules of PI/PNBE improved,as same as the crystallization and mechanical properties.The group contribution method demonstrated that DMF was a suitable solvent with strong polarity with monomer PMDA,but low polarity with ODA.Infrared spectroscopy and rotational viscometer showed that the polycondensation reaction during the preparation process of PAA would completed in 140 min with a fast reaction speed in middle period,and the final reaction degree was about 86.93%.In drying process,the solvent evaporated rapidly in the first 50 min,and the higher temperature or lower solid content was,the faster evaporate and smaller residual mass would be.The physical model was found by discrete method,and the simulation results of volume fraction were consistent with the experimental value,which proved the rationality of the model.It showed that the higher temperature or lower solid content,the faster the evaporation would result in the the volume fraction changed faster.The concentration would gradually decrease from solution-substrate interface to solution-gas phase interface,which is accompanied by the effect on coating surface,and crust would become more obvious and finally solidified under higher temperature or lower solid content.It demonstrated that the self-diffusion coefficient was higher than that of the mutual diffusion coefficient,and would gradually decreased with the drying process.On the contrary the mutual diffusion coefficient would increase,and the higher the temperature or lower solid content,the greater mutual diffusion coefficient would be.