MOLECULAR-DYNAMICS STUDY OF THE MIXING AND DEMIXING OF A BINARY LENNARD-JONES FLUID

Dynamic properties of a binary Lennard-Jones mixture at various temper atures and two densities are studied using a molecular dynamics comput er simulation starting from mixed and separated initial configurations . After deriving an analytical correction term for finite size effects , the rate of separation is determined as a function of temperature, w hich is influenced by two counteracting trends: at higher particle vel ocities demixing becomes faster, but with increasing temperature the s eparated state becomes less stable. At both densities studied, we obse rve an increase in the rate of separation with increasing temperature. In a second step, a small number of a third type of particle represen ting a crude model of an amphiphilic molecule is added and the results are compared with those of the binary mixture case. Owing to a dip in the density at the binary fluid interface, the amphiphilic molecules collect in a slit and as a result, no effect on the separation behavio ur of the system is observed. At those temperatures for which the sepa rated configuration is stable, the typical behaviour of the individual particle is analysed.