Phenomenological Theory of Prefreezing at the Solid-Melt Interface

Crystallization of liquids often starts at the interface to a solid. The underlying process can be either heterogeneous nucleation or the recently observed process of prefreezing. The latter is the reversible abrupt formation of a crystalline layer at the melt-solid interface at temperatures T_max above the bulk melting point. We present a phenomenological theory of prefreezing and derive such equilibrium properties as the temperature dependent thickness of the prefrozen layer, the prefreezing temperature T_max, and the mesoscopic jump of thickness l_min at T_max.¹ The theory provides a clear thermodynamic explanation of the abrupt formation of a crystalline layer resulting from the interplay of the interfacial energies of the substrate-crystal γ_sub,cry, crystal-melt γ_cry,melt, and substrate-melt γ_sub,melt interfaces. It is found that while the prefreezing temperature T_max depends primarily on the difference of the interfacial energies Δγ = γ_sub,melt – (γ_sub,cry + γ_cry,melt), the minimum jump of thickness l_min is controlled by the ratio (γ_sub,cry + γ_cry,melt) / γ_sub,melt. Thus, T_max and l_min can vary independently.

[1] Dolynchuk et al. J. Phys. Chem. Lett. 2019, 10 (8), 1942-1946.