Micro-scale simulation of adsorption-diffusion behaviors of nanoparticles onto mobile oil/water interface

Abstract

A novel, hybrid pore-scale simulation method using Lattice-Boltzmann (LB) coupled with Langevin-Dynamics (LD) is proposed to investigate the physics of nanoparticles onto oil/water interface. Based on the LB method, the high-resolution characterization of oil-water interface is established. Then, in a fashion of discrete LB forcing source distribution, the LD method is introduced to characterize the effects of Brownian motion, thermal fluctuation-dissipation, multi-body hydrodynamics, and particle-particle interactions. By the means of the new LB-LD coupling model, the adsorption and diffusion characterization of nanoparticles onto oil/water interface are investigated. Moreover, by introducing the interference coefficient and non-equilibrium time, a modified Langmuir adsorption equation is first established by more accurately quantifying the adsorption characterization of nanoparticles and the consequent impacts onto the oil/water interfacial force (IFT), which cannot be accurately described by the classical Langmuir model. For the example of SiO2 nanoparticles adsorption, it is observed that small-size nanofluids with high concentration could accelerate the adsorption of nanoparticles. In addition, both the lateral and longitudinal diffusion coefficients of nanoparticles in the water phase and onto interface are obtained, and of which the underlying mechanisms are explained by introducing residual oil. The proposed simulation method provides valuable insights into how nanoparticles adsorb and diffuse onto oil/water interface and how oil/water IFT can be reduced.