Structure and dynamics of binary liquid mixtures near their continuous demixing transitions

Abstract

The dynamic and static critical behavior of a family of binary Lennard-Jones liquid mixtures, close to their continuous demixing points (belonging to the so-called model H' dynamic universality class), are studied computationally by combining semi-grand canonical Monte Carlo simulations and large-scale molecular dynamics (MD) simulations, accelerated by graphic processing units (GPU). The symmetric binary liquid mixtures considered cover a variety of densities, a wide range of compressibilities, and various interactions between the unlike particles. The static quantities studied here encompass the bulk phase diagram (including both the binodal and the λ-line), the correlation length, and the concentration susceptibility, of the finite-sized systems above the bulk critical temperature T, the compressibility and the pressure at T. Concerning the collective transport properties, we focus on the Onsager coefficient and the shear viscosity. The critical power-law singularities of these quantities are analyzed in the mixed phase (above T) and non-universal critical amplitudes are extracted. Two universal amplitude ratios are calculated. The first one involves static amplitudes only and agrees well with the expectations for the three-dimensional Ising universality class. The second ratio includes also dynamic critical amplitudes and is related to the Einstein-Kawasaki relation for the interdiffusion constant. Precise estimates of this amplitude ratio are difficult to obtain from MD simulations, but within the error bars our results are compatible with theoretical predictions and experimental values for model H'. Evidence is reported for an inverse proportionality of the pressure and the isothermal compressibility at the demixing transition, upon varying either the number density or the repulsion strength between unlike particles.

Finite-size scaling study of dynamic critical phenomena in a vapor-liquid transition

“…On the other hand, the situation with respect to dynamics is relatively poor. Simulation studies, that helped achieving the objective for the static phenomena, gained momentum in the context of dynamic critical phenomena only recently [25][26][27][28][29][30][31][32][33][34][35][36][37][38]. Such a status is despite the fact that adequate information on the equilibrium transport phenomena is very much essential for the understanding of even nonequilibrium phenomena like the kinetics of phase transitions [9,39].…”

Stresses in non-equilibrium fluids: Exact formulation and coarse-grained theory

“…In this section, we make use of the expressions derived for the microscopic stress tensor Eq. (19) to compute the two-point correlations of the stress at different positions and times for a bulk equilibrium system. We provide the limit of high temperatures, which corresponds to the leading-order term in the external potential V .…”

Surface-induced nonequilibrium dynamics and critical Casimir forces for model B in film geometry

“…As far as future studies are concerned, it would be interesting to assess to which extent the actual critical dynamics of a fluid film (model H) differs from that of model B. This could be addressed, e.g., via Molecular Dynamics or Lattice Boltzmann simulations [56][57][58]. Extending the present study to (+−) boundary conditions appears to be a natural and rewarding step.…”