Why is the thermal conductivity of Janus nanofluid larger? - From the perspective of aggregation morphology

The nanoparticle aggregation is a crucial factor for the thermal conductivity of nanofluids based on previous researches. Molecular dynamics simulations for the nanofluids involving 4-32 Janus nanoparticles (termed as Janus nanofluid) were conducted. The thermal conductivity of the Janus nanofluid was found to be larger than that of the ordinary nanofluid, approximately 0.3707 W/m.K for Janus, compared to 0.3521 W/m.K for Au and 0.3303 W/m.K for Cu nanofluid. Further analysis shows that the aggregation morphology in the Janus nanofluid is different from that in the ordinary one. For the better evaluation of the aggregation morphology, a term named degree of looseness was introduced to replace fractal dimension. The relationship between thermal conductivity and degree of looseness shows that the thermal conductivity of the Janus nanofluid first rises and then decreases with the degree of looseness. When 18 nanoparticles are included in the simulated system, the maximum thermal conductivity is 0.3249 W/m.K for a moderate degree of looseness of 10.841 at 4 vol%. Finally, the underlying mechanism why the Janus nanofluid has a larger thermal conductivity than the ordinary one is discussed. This can provide a useful reference for preparing Janus nanofluids with larger thermal conductivity and understanding the underlying mechanisms.