Structure And Properties Of PI And PI/ZnO From First Principles

Polyimide (PI) is a polymer chain of heterocyclic compounds with the half-ladder and ring structure. These polymers, with outstanding heat resistance, goodmechanical properties, electrical properties and stability, various products ofwhich such as molding compounds, composites, adhesives, membranes have beenwidely used in aerospace, electronic industry, light communication, bulletproofmaterials, and gas separation etc. However, the polyimide has poor solubility,processing difficulties, the high dielectric constant, high rate of moistureabsorption, partial discharge resistant performance can not meet the requirementsof frequency modulation. The method to improve polyimide comprehensiveperformance mainly is inorganic nanoparticles incorporated into polyimide, theissue becomes more and more concern of researchers.This article is based on the first principles density functional theorypseudopotential plane wave method, optimizing the package model of PI ingeometry and electronic structure, used energy band structure and density of stateto calculate the optical properties, and carried out a systematic theoreticalanalysis, theoretically explored the characteristics of the PI materials in thephotovoltaic sector. Then, using the force field method, we research the effect ofparticle size of nano-ZnO on the surface binding energy in PI/ZnO composites.It is easy found the most suitable inorganic nano particle size to achieve the idealinterfacial adhesion. Moreover, it can be obviously seen that the form of nano-ZnO and PI intermolecular bonding and improve the performance of theinorganic nano-hybrid materials fundamentally. The simulated results were ingood agreement with the experimentally ones, implicating they are helpful foroptimization of the experiment design.From the atom orbit electron occupies number and net charge distribution ofPI we know that N atoms and O atoms have relatively strong ability of electrons and negatively charged and the C atoms lose electrons and has positively charged;PI molecular orbital is mainly O atom2P orbit and C atom2P orbit, the results isconsistent with the analysis results of the density of states. PI band structurecalculated energy gap is1.9eV, the experimental value of2.74eV. The energygap of absorption spectra1.57eV, the imaginary part of dielectric absorptionband edge is about1.42eV. The PI frontier molecular orbital distribution indicatethat the PI of the highest occupied molecular orbitals HOMO is mainlyconcentrated on the benzene ring, the electron cloud of the lowest unoccupiedmolecular orbital LUMO is mainly the contribution of the imide ring.The simulation results of the surface binding energy between the PI andZnO show that the surface binding energy in PI/ZnO composites increases withincreasing the nano ZnO radius; when the radius of nano-ZnO greater than1.5nm,the binding energy increased slowly, and the maximum of binding energy is1236.2kcal/mol; moreover, it can be obviously seen that the form of nano-ZnOand PI intermolecular bonding is mainly molecular bonds.