Thermodynamic Concepts of the First-Order Prefreezing

An interaction with a solid surface can induce crystallization in liquids by either heterogeneous nucleation or prefreezing. The latter is seen as the crystalline layer formation at an interface to a solid substrate at temperatures higher than that of a bulk crystal. Most recently, it was ascertained that prefreezing is a first-order transition, since the formation of the crystalline phase is abrupt and reversible.
We introduce a phenomenological theory of prefreezing and analyze such equilibrium properties as the temperature dependent crystal thickness, the maximum melting temperature T_max, and the mesoscopic jump of thickness during melting or crystallization. The theory enables a clear first-principles explanation of the abrupt formation of a crystalline layer, i.e., the first-order nature of prefreezing and defines the corresponding transition temperature T_max as a function of the interfacial free energies. We show that it is the difference of the interfacial energies that controls T_max and acts as a driving force for prefreezing. The analytical outcomes are congruent with recent experimental results for poly(ε-caprolactone) crystallized on graphite via prefreezing.