Matching macroscopic properties of binary fluids to the interactions of dissipative particle dynamics

We investigate the role played by conservative forces in dissipative particle dynamics (DPD) simulation of single-component and binary fluids. We employ equations from kinetic theory for matching the coefficients of DPD interparticle force to the macroscopic properties of fluid such as: density, temperature, diffusion coefficient, kinematic viscosity and sound velocity. The sound velocity c is coupled with scaling factor π₁ of conservative component of the DPD collision operator. Its value sets up an upper limit on the mass S of a single particle in DPD fluid. The Kirkwood-Alder fluid-solid transition is observed for a sufficiently large S. We emphasize the role of the scaling factor π₁₂ for particles of different types in simulating phase separation in binary fluids. The temporal growth of average domain size R(t) in the phase separation process depends on the value of immiscibility coefficient Δ = π₁₂ - π₁. For small immiscibility, R(t) ∝ t^β, where β ≈ 1/2 for R(t) < R_H and β ≈ 2/3 for R(t) > R_H, R_H is the hydrodynamic length. Finally, both phases separate out completely. For larger immiscibility, R(t) increases exponentially at the beginning of simulation, while finally the domain growth process becomes marginal. We also observe the creation of emulsion-like structures. This effect results from an increase of the surface tension on the two-phase interface along with increasing immiscibility.