Hydrodynamics of immiscible binary fluids with viscosity contrast: a multiparticle collision dynamics approach

Area of Science:

• Computational physics
• Fluid dynamics
• Soft matter physics

Background:

• Understanding fluid dynamics at interfaces is crucial for various applications.
• Continuum hydrodynamics provides a macroscopic view but lacks microscopic detail.
• Multiparticle collision dynamics (MPC) offers a mesoscopic approach to simulate complex fluids.

Purpose of the Study:

• To implement and validate a multiparticle collision dynamics (MPC) model for layered immiscible fluids with different shear viscosities.
• To compare MPC simulations of fluid flow and shear stress with continuum hydrodynamics predictions.
• To investigate the hydrodynamic mobility of colloidal spheres near fluid-fluid interfaces using the MPC model.

Main Methods:

• Implementation of a multiparticle collision dynamics (MPC) model for two immiscible fluid layers (A and B) with distinct shear viscosities.
• Simulation of steady shear flow and analysis of time-dependent shear stress functions.
• Calculation of wave-vector dependent transverse velocity auto-correlation functions (TVAF) in bulk fluid regions.
• Determination of hydrodynamic mobilities for a colloidal sphere moving parallel and transverse to the fluid-fluid interface at varying distances.

Main Results:

• MPC simulations of flow profiles and shear stress functions showed excellent agreement with continuum hydrodynamics results.
• Exponential decay of TVAF in bulk fluid regions matched predictions for single-phase MPC fluids.
• Hydrodynamic mobilities of colloidal spheres near the interface agreed well with hydrodynamic force multipoles calculations for creeping flow.
• The MPC model demonstrated straightforward implementation and computational efficiency.

Conclusions:

• The developed MPC fluid-layer model is a computationally efficient and accurate tool for simulating immiscible fluid interfaces.
• The model successfully reproduces key hydrodynamic behaviors, including flow profiles, shear stress, and colloidal mobility.
• While effective, the spatial discretization of MPC limits the reproduction of all features of an ideally flat interface.