Factors that influence the aggregation structure of nanoparticles in nanofluids: A molecular dynamics simulation

Nanofluids have received considerable attention from researchers due to their excellent heat transfer properties compared with traditional heat transfer media. The aggregation structure of nanoparticle agglomerates is one of the important mechanisms for the enhanced thermal conductivity of nanofluids. In this study, molecular dynamics was used to study the factors that influenced the aggregation structure of nanoparticle agglomerates in Cu–Ar nanofluids. The aggregation behavior of two and four nanoparticle agglomerates at different particle sizes and initial distances was simulated. The results show that when the initial distance of nanoparticle agglomerates is 4 Å, the increase of particle size does not change the aggregation structure to reaction-limited aggregation. When the initial distance is 3 Å, the nanoparticle agglomerates form a reaction-limited aggregation structure after the particle size increases beyond a threshold value (two nanoparticle agglomerates with the same particle size: 10 Å; two nanoparticle agglomerates with different particle sizes: 9 Å; four nanoparticle agglomerates with the same particle size: 5 Å). This indicates that there is a threshold value for the initial distance of nanoparticle agglomerates. When the initial distance is larger than the threshold value, the nanoparticle agglomerates cannot break the repulsive barrier and form reaction-limited aggregates, no matter how the particle size increases. When the initial distance is less than the threshold value, the particle size becomes a key factor in determining the aggregation structure.