Microbeam X-ray diffraction analysis of interfacial heterogeneous nucleation of n-hexadecane inside oil-in-water emulsion droplets

We have carried out X-ray microbeam analysis of the crystallization behavior of n-hexadecane (C16) in oil-in-water emulsion droplets that were formed using surfactants with different types of hydrophobic moieties. It was confirmed that molecular-shape matching between the hydrophobic moiety and C16 caused the following crystallization behavior: when the molecular shape of the hydrophobic moiety was similar to C16, high-intensity X-ray diffraction of the rotator phase of C16 was detectable at the initial stage of crystallization and the long-chain axes of C16 crystals aligned normal to the membrane interface. The present results provided the first evidence of interfacial heterogeneous nucleation caused by molecular interactions at the emulsion membrane, which is thought to be related to the interfacial freezing that was observed at the oil-water interface with surfactants in a bulk system.