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 similar to 67 nm, similar to 280 nm, and similar to 1.9 mu m, 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 degrees C at the corresponding planar interface. Differential scanning calorimetry and optical microscopy data show that the similar to 280 nm and similar to 1.9 mu m droplet systems induce ice formation at temperatures up to -8 +/- 2 to -9 +/- 2 degrees C, for 1-heptacosanol interfacial concentrations of similar to 2-8% and similar to 4-11%, respectively. In comparison, ice nucleation only occurs at temperatures up to -13 +/- degrees C in the similar to 67 nm droplets, which have higher interfacial 1-heptacosanol concentrations of between similar to 9 and 21%. The extended classical nucleation theory is insufficient to explain the extent of the reduced nucleating ability in the similar to 67 nm nanoemulsions, and so we propose that the nucleating ability of 1-heptacosanol is also reduced as the interfacial curvature increases.