Enthalpy versus entropy: What drives hard-particle ordering in condensed phases?

Abstract

In support of mesoscopic-scale materials processing, spontaneous hard-particle ordering has been actively pursued for over a half-century. The generally accepted view that entropy alone can drive hard particle ordering is evaluated. A thermodynamic analysis of hard particle ordering was conducted and shown to agree with existing computations and experiments. Conclusions are that (i) hard particle ordering transitions between states in equilibrium are forbidden at constant volume but are allowed at constant pressure; (ii) spontaneous ordering transitions at constant pressure are driven by enthalpy, and (iii) ordering under constant volume necessarily involves a non-equilibrium initial state which has yet to be rigorously defined.