First study on the effects of interfacial curvature and additive interfacial density on heterogeneous nucleation. Ice crystallization in oil-in-water emulsions and nanoemulsions with added 1-heptacosanol

Extended classical nucleation theory predicts that heterogeneous crystallization on a convex substrate will be less efficient than for the planar case. In this article, we present the first systematic study of the effects of interfacial curvature on crystallization. Decane-in-water nanoemulsions and emulsions have been prepared with droplet sizes of ∼67 nm, ∼280 nm, and ∼1.9 μm, which are stabilized by the passive nonionic surfactant, Brij 30. Ice nucleation is induced at the curved decane-water interface by 1-heptacosanol, which can cause ice formation at temperatures as high as -4.5 to -7°C at the corresponding planar interface. Differential scanning calorimetry and optical microscopy data show that the ∼280 nm and ∼1.9 μm droplet systems induce ice formation at temperatures up to -8 ± 2 to -9 ± 2°C, for 1-heptacosanol interfacial concentrations of ∼2-8% and ∼4-11%, respectively. In comparison, ice nucleation only occurs at temperatures up to -13 ± 2°C in the ∼67 nm droplets, which have higher interfacial 1-heptacosanol concentrations of between ∼9 and 21%. The extended classical nucleation theory is insufficient to explain the extent of the reduced nucleating ability in the ∼67 nm nanoemulsions, and so we propose that the nucleating ability of 1-heptacosanol is also reduced as the interfacial curvature increases.