Do supercooled liquids freeze by spinodal decomposition?

Two questions are addressed in this paper: Is it likely that spinodals occur in the freezing of one-component liquids at degrees of supercooling as moderate as T/T melt=0.6, and are the ramified solidlike structural fluctuations seen in simulations of supercooled liquids the tell-tale harbingers of spinodal decomposition? It has been suggested in several papers that in the freezing of argonlike systems, a spinodal can be expected to be encountered at T/T melt of approximately 0.6 or even at a shallower degree of supercooling. Heuristic evidence, particularly that found in molecular dynamics simulations in the system of selenium hexafluoride, a substance with properties similar in several respects to those of argon, suggests that a spinodal does not occur at supercoolings even considerably deeper than T/T melt=0.6. Reinforcing this conclusion are arguments based on nucleation kinetics in the Appendix. It has been found that many of the very thin, ramified solidlike fluctuations encountered in simulations of deeply supercooled liquids do not, in themselves, qualify as true nuclei for freezing but do, nevertheless, significantly influence the properties of the liquids. They contribute to the breakdown of the Stokes-Einstein relation universally found in supercooled liquids, liquids which have not been seen to exhibit a spinodal. Although such ramified fluctuations have been postulated to be precursors of spinodal decomposition, that role has not yet been confirmed.