Crystallization on encapsulated systems such as micelles, vesicles, emulsions, cubic phases etc, are highlighted recently because it will be potentially able to control nucleation and crystal growth rate, and to select the crystallization of the special polymorphs. In this presentation, crystallization of oil droplet in oil-in-water emulsion system are focused on the following two results: (i) crystallization of new polymorph appeared in oil phase of n-hexadecane-in-water emulsion measured by time-resolved synchrotron radiation small- and wide-angle X-ray scattering (SAXS/WAXS) and differential scanning calorimetry (DSC) simultaneous method. In more detail, n-hexadecane-water emulsion system was prepared by high-pressure homogenization techniques. The average droplet size was ~1 micro meter. Tween 20 was put as an emulsifier. When the high-melting hydrophobic emulsifiers was added to n-hexadecane, the model of oil phase in O/W emulsion, the hexagonal and orthorhombic type polymorphs appeared as new polymorphic forms in O/W emulsion together with triclinic type polymorph which was observed only in bulk system. These new polymorphs would be crystallized on the oil-water interface of oil droplets after the added high-melting hydrophobic emulsifiers crystallized. In other words, the high melting emulsifier plays a role of the template for heterogeneous nucleation and following crystal growth of the new polymorphs. These new polymorphs were observed more than 0.1 wt% concentration of the high-melting emulsifiers. On the other hand, no new polymorph was observed without high-melting hydrophobic emulsifiers added in the oil phase of O/W emulsion. However, when we prepared the larger droplet size, such as 30 or 40 micro meter, of n-hexadecane droplet in O/W emulsion system, the transient rotator phase, meaning hexagonal phase, was observed without any high-melting emulsifiers in oil droplet of O/W emulsion. (ii) Clarifying the template effect occurred on the oil-water interface described above, synchrotron radiation micro-beam analysis has been done. The 5 x 5 micro meter-sized micro-beam is hit a specific area in an oil droplet and the diffraction from the area is detected. The 30 ~ 50 micro meter droplet samples were prepared. Imaging plate and image intensifier connected with CCD camera type two dimensional detector were employed. When the micro-beam was hit the center of a droplet, a circle-like diffraction peaks appeared, meaning a lot of small single crystals existed. On the other hand, when the micro-beam was hit the edge of a droplet, i.e. the oil-water interface, arc-like diffraction peak appeared. In addition, the micro-beam was hit the edge rotated the right angle from the previous edge of the same droplet, arc-like diffraction peak rotated the right angle appeared, meaning the existence of the lamellar structure along the oil-water interface. The same kind of result has been obtained in the triacylglycerol-in-water emulsions. From above results, it is clear that the heterogeneous nucleation occurred on the oil-water interface of oil droplet of oil-in-water emulsion.

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