Variation of Gibbs free energy for a transition from the liquid state to solid state. (A) Relationship between the nucleation radius and Gibbs free energy. (B) Relationship between the temperature and Gibbs free energy. (C) Labile-cluster model of hydrate nucleation [37]. Copyright © 2020, Royal Society of Chemistry. Note: ΔG denotes the Gibbs free energy; ΔG(r _c) denotes the Gibbs free energy corresponding to the critical radius; Δg and ΔT denotes the difference in free energy per unit volume and supercooling degree of PCMs, respectively.