Surface modification boosts dispersion stability of nanoparticles in dielectric fluids

Achieving stable dispersion of nanoparticles in dielectric fluids is a challenging task, as there are complex and diverse influencing factors, requiring molecular-level understanding of the nanoparticle aggregation. In this paper, we conducted long-time molecular simulations of dielectric nanofluids containing fifteen SiO2 nanoparticles, systematically varying the length of alky chains grafted onto their surface to explore their impact on the aggregation process. Our results reveal that appropriate surface modification can dramatically increase the dispersion stability of nanoparticles in dielectric fluids. SiO2 nanoparticles lacking alkyl chains exhibit a strong tendency to approach each other, and form aggregates in natural esters, because of the Coulombic energy from heteroatoms of SiO2 nanoparticles. Despite the differences in the length of grafted alkyl chains on the surface of SiO2 nanoparticles, all of them, regardless of their length, are capable of effectively shielding the Coulombic interactions and increasing the van der Waals interaction with natural esters, thereby reducing the aggregation tendency of nanoparticles. Furthermore, the smaller diffusion ability, caused by the steric hindrance effect, of surface-modified SiO2 nanoparticles also inhibits their collision and subsequent aggregation.