Molecular-dynamics study on the thermodynamic properties of nano-SiO₂ particle-doped silicone rubber composites

Polymer dielectric materials doped with nanoparticles show promising applications in the insulation of electrical equipment. In experiment, however, the doping amounts of nanoparticles significantly affect the mechanical and dielectric properties of polymer nanodielectrics. In this paper, the doping amounts and agglomeration of nanoparticles are considered in molecular dynamics (MD) simulations to reveal the probable microscopic mechanism. The effects of doping amounts and agglomeration of nano-SiO₂ particles on the thermodynamic properties of silicone rubber (SR) nanocomposites are studied from the aspects of the mean square displacement, free volume fraction, pore size distributions, interaction energy, cohesive energy density and hydrogen bond analysis. The results show that with increasing doping amounts of nano-SiO₂, the interfacial interactions and intermolecular force of the SR composites are enhanced. Therefore, the mean square displacement, the free volume fraction and the maximum pore size for SR composites all decrease, which is beneficial to the improvement of mechanical and dielectric performances for nano-SiO₂/SR composites. However, the agglomeration of nano-SiO₂ particles (the increase of the size of nanoparticles), will lead to a decline in the intermolecular forces among SR chains and the destruction of hydrogen bond networks. Therefore, the mean square displacement, the free volume fraction and the maximum pore size in SR composites will increase, which will degrade the mechanical and dielectric performances of SR composites. This work reveals a generalized relationship between the doping amounts and agglomeration of nanoparticles and the thermodynamic properties of polymer dielectric composites.