Molecular dynamics investigation of shape-dependent viscosity of silver-water nanofluids

Silver-water nanofluids provide superior heat transfer performance and high chemical stability against aqueous oxidation, making them promising heat transfer media for advanced thermal management applications. Shear viscosity is as essential as thermal conductivity because it dictates pumping power. However, unlike thermal properties, the specific effect of nanoparticle shape on nanofluid viscosity has not been completely investigated. Although the nanoparticle surface-to-volume ratio is known to affect thermal properties, its specific influence on nanofluid viscosity remains insufficiently explored. This study evaluates the effects of nanoparticle shape, size, volume fraction, and temperature on the dynamic viscosity of Ag-water nanofluids.

In this study, equilibrium molecular dynamics (EMD) simulations are carried out via the LAMMPS software package under periodic boundary conditions. Silver-silver interatomic forces are described by the embedded-atom method (EAM) potential, whereas the rigid four-site TIP4P/2005 model is utilized for the simulation of water. Cross-interactions between Ag and water atoms are parameterized using the 12-6 Lennard-Jones (LJ) potential. The shear viscosity is obtained with the time integration of the shear stress autocorrelation function via the Green-Kubo method. The results indicate that all studied factors significantly affect the nanofluid viscosity. In particular, the geometrical impact is strongly associated with the surface-to-volume ratio, where shapes with higher surface-to-volume ratios induce greater interfacial structuring and flow resistance, exerting a profound influence on the rheological behavior of nanofluids. Overall, these results provide fundamental atomic-level insights into the hydrodynamic efficiencies and flow behaviors of nanofluid systems.