Fragmentation of hot classical drops

Abstract

Time evolution of hot drops of matter containing ∼230 or ∼130 particles is studied by classical molecular dynamics. Initially, the drops have uniform density and a sharp surface. The chosen initial conditions include three values of density and a range of temperatures wide enough to study the phenomena of evaporation, fragmentation, and total vaporization in a unified fashion. The average density and temperature of central matter is measured periodically to obtain trajectories of the evolution in the ρ,T plane. These trajectories indicate that the matter expands almost adiabatically until it reaches the region of adiabatic instabilities. Density inhomogeneities develop in this region, but the matter fragments only if the expansion continues to average densities of less than one-fourth the liquid density, otherwise it recondenses into a single blob. The recondensed matter and fragments have very crooked surfaces. If the temperature is high enough, the expanding matter does not enter the region of adiabatic instabilities and totally vaporizes. For initial densities of the order of equilibrium density, matter does not fragment or develop large inhomogeneities in the region enclosed by the isothermal and adiabatic spinodals. Thus it appears unlikely that fragmentation of small drops (nuclei) can be used to study the isothermal critical region of gas-liquid phase transition. A detailed tabulation of the energies and number of monomers, dimers, light, and heavy fragments emitted in each event is presented.