Lattice Boltzmann simulations of anisotropic particles at liquid interfaces

Abstract

a b s t r a c tComplex colloidal fluids, such as emulsions stabilized by particles with complex shapes, play an important role in many industrial applications. However, understanding their physics requires a study at sufficiently large length scales while still resolving the microscopic structure of a large number of particles and of the local hydrodynamics. Due to its high degree of locality, the lattice Boltzmann method, when combined with a molecular dynamics solver and parallelized on modern supercomputers, provides a tool that allows such studies. Still, running simulations on hundreds of thousands of cores is not trivial. We report on our practical experiences when employing large fractions of an IBM Blue Gene/P system for our simulations. Then, we extend our model for spherical particles in multicomponent flows to anisotropic ellipsoidal objects rendering the shape of, e.g., clay particles. The model is applied to a number of test cases including the adsorption of single particles at fluid interfaces and the formation and stabilization of Pickering emulsions or bijels.

Adsorption of Ellipsoidal Particles at Liquid–Liquid Interfaces

“…Comparing this observation of a region of constant initial angle with the calculations of De Graaf et al 31 and Gunther et al 32 , which identify the capillary force as the driving force for adsorption, suggests that the particle penetrates the interface before reorienting, as this pathway corresponds to the fastest changes in free energy. However, there are some significant differences with the simulations.…”

“…However, the free energy method does not take into account interfacial deformation and colloidal interactions. Günther et al 32 used a more elaborate simulation, using a combined multicomponent lattice Boltzmann and molecular dynamics approach. Similar to De Graaf et al, adsorption trajectories are complicated and non-monotonic.…”

Detachment energies of spheroidal particles from fluid-fluid interfaces

“…30,35,45,46 The LB method can be considered an alternative to traditional Navier-Stokes solvers for fluids and due to its local nature is well suited for implementation on supercomputers. While elaborate descriptions of the model implementation have been published previously, 30,31,36,39 we revise some relevant details for the present work in the following.…”

“…30,39 All lattice sites in the outer shell of a particle are filled with a virtual binary liquid which itself is not governed by the LB equation but participates in the computation of the Shan-Chen interaction forces. The densities of those virtual liquids (vl) are…”

“…[28][29][30][31] LB simulations 28,29,[32][33][34][35] can play an important role in understanding the fundamental interactions between particles and interfaces and elucidate the behaviour of macroscopic systems such as Pickering emulsions, bijels, and capillary suspensions. 30,31,[36][37][38][39] In the Shan-Chen multicomponent LB model 28,29 that we utilise in this paper, surface-tension emerges from the fundamental mesoscopic interactions of particle distribution functions that the algorithm describes. No assumptions are made about the dynamics of the contact line during detachment.…”