Molecular Dynamics Study of the Influence of Nano SiO(2) on the Thermodynamic Properties of PMIA Composites

The poly-m-phenyleneisophthalamide (PMIA) is widely used in the electrical field due to its numerous favorable characteristics, but its poor thermal conductivity limits its application. In this study, PMIA was modified with nano-silica (SiO(2)) to improve its thermal and mechanical properties. Using iso-phthalic acid and m-phenylenediamine as monomers, the changes in the thermodynamic properties and microstructure parameters of SiO(2)-modified PMIA were analyzed using molecular dynamics before and after modification in the temperature range of 250~450 K. It was found that adding SiO(2) improves the Young’s modulus and Shear modulus of PMIA, and the mechanical properties of PMIA, and SiO(2)/PMIA composites deteriorate with increasing temperature, but the mechanical properties of SiO(2)/PMIA composites are always better than those of pure PMIA in the temperature range of electrical equipment. Meanwhile, after doping SiO(2) with the radius of 8 Å, the glass transition temperature of PMIA increases by 27.11 K, and its thermal conductivity increases from 0.249 W m(−1) K(−1) to 0.396 W m(−1) K(−1). When SiO(2) is added to PMIA, the thermal expansion coefficient of PMIA will decrease in both glass and rubber states, and its thermal stability will improve. In terms of microstructure parameters, the free volume distribution of the SiO(2)/PMIA model is less easily dispersed than that of the PMIA model, indicating that the addition of SiO(2) can improve the related properties of PMIA by hindering the movement of molecular chains.