Interfacial interaction–driven rheological properties of quartz nanofluids from molecular dynamics simulations and density functional theory calculations

Abstract

Correlations of the shear viscosity of quartz nanofluids with particle concentration, particle size, and temperature were investigated with molecular dynamics simulations and density functional theory (DFT) calculations. A new understanding to the experimentally concluded correlations was addressed in terms of microscopic particle–water interfacial interaction in three aspects. First, the viscosity of quartz nanofluids at different particle concentrations, particle sizes, and temperatures were simulated using the equilibrium molecular dynamics simulations method to reproduce the experimental observations. At the same particle size, the nanofluid viscosity decreases significantly with temperature and increases with nanoparticle volume concentration, and at the same volume concentration, the nanofluid viscosity increases with the decrease of particle size. Second, DFT calculations confirm a stronger particle–water interaction than that among water molecules. The important role of particle–water interaction in the viscosity determination of nanofluids was revealed. Finally, a correlation was proposed to fit the simulated results and compared with earlier two-parameter correlations. One parameter in the correlation is indeed a constant, while the other is a function of SiO2–water interaction energy. Our study proposes a physical basis for the experimentally concluded correlations on the viscosity of nanofluids.

Application of density functional theory to study the electronic structure and magnetic behavior of clusters MnPS3 (M = Fe, Co, Ni; n = 0 ~ 3)

“…In the article, the initial configuration of the cluster MnPS3 (n=0~3) is designed based on the topological principle by selecting the iron-based transition elements Fe, Co, and Ni as metal atoms M. Since in the field of quantum chemical calculations, B3LYP hybrid general functions [22][23] are the most widely used and comprehensive, which can perform more accurate calculations for systems containing transition metal elements and open-shell layer structures, the def2-tzvp basis set can perform all-electron operations for the first four periodic elements, and its calculation accuracy is relatively high. So the B3LYP hybridization generalized function in density functional theory [24][25] is used to calculate the transition metal elements and open-shell layer structure in cluster MnPS3, and the def2-tzvp basis group is used to perform all-electron operations on each element in cluster MnPS3, and Gaussian09 software is used to optimize the analysis of cluster MnPS3 under several different spin weights, and the optimization convergence conditions were maximum displacement <0.00180, root-mean-square displacement <0.00120, maximum force <0.00045, and root-mean-square force <0.00030. These geometrical configuration optimization calculations, frequency verification, and data processing were performed on an HP-Z440 computer using Gaussian09 and Multiwfn software packages.…”