Dynamic structure of methane/n-nonane clusters during nucleation and growth

We report results on nucleation, growth, and structure formation of methane/n-nonane clusters in an expanding system investigated by molecular dynamics simulation. From bulk phase equilibria data, it is expected that the concentration of the less volatile substance n-nonane in the clusters is very high. However, analyses of experimental data in the literature suggest somewhat higher methane content at onset of nucleation. Our simulations show that the methane mole fraction is actually very high and increases even further at the beginning of the cluster growth. On the other hand, in this transient state after nucleation the methane mole fraction in the cluster core decreases, leaving a n-nonane rich core, i.e., we observe the phase separation inside the growing cluster. Methane is squeezed out from the core to the surface and then evaporates from the surface shell during expansion of the system.