Phenomenological Theory of Prefreezing at the Solid-Melt Interface

Crystallization of liquids is usually initiated 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 and abrupt formation of a crystalline layer at the interface melt-solid at temperatures higher than 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 at T_max.¹ The theory provides a clear thermodynamic explanation of the abrupt formation of a crystalline layer as a result of the interplay of the interfacial energies γ_sub,cry, γ_cry,melt, and γ_sub,melt. The prefreezing temperature T_max was found to depend on all three interfacial energies and bulk parameters. However, we show that the difference of the interfacial energies Δγ = γ_sub,melt – (γ_sub,cry + γ_cry,melt) acts as a driving force for prefreezing, as T_max tends to increase with increasing Δγ. The analytical outcomes are in accordance with recent experimental results for polyethylene and poly(ε-caprolactone) crystallized on graphite and MoS₂ via prefreezing.

[1]. Dolynchuk et al. J. Phys. Chem. Lett. 2019, 10, 1942-46