Spinodal Decomposition in Binary Gases

We carried out three-dimensional simulations, with about $1.4\times {10}^6$ particles, of phase segregation in a low density binary fluid mixture, described mesoscopically by energy and momentum conserving Boltzmann-Vlasov equations. Using a combination of direct simulation Monte Carlo for the short range collisions and a version of particle-in-cell evolution for the smooth long range interaction, we found dynamical scaling after the ratio of the interface thickness to the domain size is less than $\sim 0.1$. The scaling length $R\left(t\right)$ grows at late times like $t^{\alpha }$, with $\alpha =1\mathrm{}$ for critical quenches and $\alpha =\frac{1}{3}$ for off-critical ones. We also measured the variation of temperature, total particle density, and hydrodynamic velocity during the segregation process.