PHASE-SEPARATION IN 2-DIMENSIONAL BINARY FLUIDS - A MOLECULAR-DYNAMICS STUDY

We present results of molecular dynamics computer simulation experimen ts of phase separation in a two-dimensional model binary fluid. For cr itical quenches the tubularlike domain structure grows at late times a ccording to a power law with an exponent 1/2 which later crosses over to 2/3. This latter result has recently been questioned by Ossadnik et al. [Phys. Rev. Lett. 72, 2498 (1994)], and we present further eviden ce that the fast exponent is indeed present in the dynamical growth. T hat these exponents are hydrodynamic in origin is demonstrated by perf orming runs where the velocity field is disturbed at regularly spaced intervals of time. The perturbation consists of resetting the velociti es of the particles to those characteristic of a Boltzmann distributio n, which destroys the hydrodynamic tail of the velocity autocorrelatio n function. The resulting exponent changes to that predicted by experi ments using stochastic techniques (Monte Carlo), i.e., 1/3. Also, we p resent results of experiments for off-critical quenches. The late-stag e growth exponent for not too off-critical concentrations is close to 1/3, but we observe a continuous transition from this exponent to that characteristic of a critical quench.