Transport phenomena and microscopic structure in partially miscible binary fluids: A simulation study of the symmetrical Lennard-Jones mixture

摘要

Static and dynamic structure factors and various transport coefficients arecomputed for a Lennard-Jones model of a binary fluid (A,B) with a symmetricalmiscibility gap, varying both temperature and relative concentration of themixture. The model is first equilibrated by a semi-grandcanonical Monte Carlomethod, choosing the temperature and chemical potential difference $\Delta \mu$between the two species as the given independent variables. Varying for $\Delta\mu=0$ the temperature and particle number $N$ over a wide range, the locationof the coexistence curve in the thermodynamic limit is estimated.Well-equilibrated configurations from these Monte Carlo runs are used asinitial states for microcanonical Molecular Dynamics runs, in order to studythe microscopic structure and the behavior of transport coefficients as well asdynamic correlation functions along the coexistence curve. Dynamic structurefactors $S_{\alpha \beta} (q,t)$ (and the corresponding static functions$S_{\alpha \beta} (q)$) are recorded ($\alpha, \beta, \in$ A,B), $q$ being thewavenumber and $t$ the time, as well as the mean square displacements of theparticles (to obtain the self-diffusion constants $D_{\rm A}$, $D_{\rm B}$) andtransport coefficients describing collective transport, such as theinterdiffusion constant and the shear viscosity. The minority species is foundto diffuse a bit faster than the majority species. Despite the presence ofstrong concentration fluctuations in the system the Stokes-Einstein relation isa reasonable approximation.