The Bulk Viscosity of a Symmetrical Lennard–Jones Mixture above and at Liquid–liquid Coexistence: A Computer Simulation Study

A Lennard–Jones model of a binary (AB) dense liquid with a symmetrical miscibility gap is investigated by means of computer simulation methods. Semigrand-canonical Monte Carlo simulations yield the phase diagram in the T–x plane (T: temperature, x: concentration of A or B particles), as well as equilibrated configurations at coexistence. Then, we undertake molecular dynamics simulations which use these configurations to determine static properties (isothermal compressibility κ T , and concentration susceptibility χ), as well as the shear and bulk viscosities ηs and ηB, respectively. The latter quantities are calculated along a path approaching the coexistence line from high temperatures in the one-phase region and ending at a state at the coexistence line about 15% below the critical point. We find that κ T and χ increase significantly near the coexistence line, reflecting the vicinity of the critical point. Whereas η s exhibits a weak temperature-dependence, ηB increases significantly near the coexistenc...