Controlling Polymorphic Crystallization of n -Alkane Crystals in Emulsion Droplets through Interfacial Heterogeneous Nucleation

It was found that even-numbered n -alkanes (number of carbon atoms = 16−22) had a crystal structure that has not been reported for their bulk phase when the n -alkanes were nucleated in oil-in-water emulsion droplets with additives. We measured wide- and small-angle X-ray diffraction signals, using synchrotron radiation, at the same time that the nucleation was determined by differential scanning calorimetry. When high-melting-point surfactants were added to the droplets, pseudohexagonal and orthorhombic crystals were nucleated. In contrast, triclinic crystals formed in the droplets without the additive, and in bulk liquid both with and without the additives. The results were discussed by taking into account interfacial heterogeneous nucleation accelerated by freezing of the adsorbed films of the additive molecules at the oil−water interface. These findings indicate that emulsion can be used to form a new crystalline polymorphic structure by using suitable additives that modify interfacial heterogeneous nucleation behavior.