The microbeam X-ray diffraction study for the crystallization process of oil phase in oil-in-water emulsion

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In this research subject, the following results have been obtained ;(1)Results for macro-beam (synchrotron X-ray beam of mm-sized diameter)1-1.In the oil-in-water (O/W) emulsion whose oil phase consisted of even-numbered n-alkanes, 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. It is suggested that interfacial heterogeneous nucleation occurred at the oil-water interface by freezing of the adsorbed films of the additive molecules. These results indicate that emulsion can be used to form a new crystalline polymorphic structure by using suitable additives that modify interfacial heterogeneous nucleation behavior.1-2.On the large sized O/W emulsion, without additives, whose oil phase consisted of n-hexadecane, a transient rotator phase was observed. Thus we confirmed the existence of rotator phase in n-hexadecane that was observed in bulk samples. It is suggested that the rotator phase at the oil-water interface plays a precursor role for bulk crystallization.(2)Results for micro-beam (synchrotron X-ray beam of μm-sized diameter)2-1.When microbeam X-ray passed through the edge of an oil droplet which was the O/W emulsion with additives under crystallization temperature, two kinds of diffraction peak appeared; pseudohexagonal and triclinic. In contrast, only a diffraction peak from triclinic polymorph appeared when the microbeam passed through the center of an oil droplet of the same sample. These results suggest that the template film exists at the oil-water interface and n-hexadecane near the interface is crystallized as a pseudohexagonal polymorph in the influence of the teplate film.2-2.A lot of crystals exist in an oil droplet whose diameter is more than 10 μm. Each crystal size was estimated less than 3 μm by scanning the microbeam.