Pickering Emulsions Stabilized with Millimeter-Sized Polymer Plates

Hexagonal polymer plates of (sub)millimeter size that were uniform in shape and size were used as a stabilizer for emulsions, and the correlations of plate size, oil polarity, and plate dispersing media before emulsification with the formability, type, and droplet shape of emulsions were studied. The formability of the emulsions was improved by decreasing the plate size. The lower the oil polarity was, the more preferably O/W-type emulsions were formed, and as the oil polarity increased, the formability of W/O-type emulsions increased, whereas too high of an oil polarity resulted in no emulsion formation or macrophase separation of the oil dispersion of the plates and water. Furthermore, when the plate dispersing medium before emulsification was oil, the plates tended to be lipophilic compared with those dispersed in water before emulsification. In addition, we confirmed that there was a correlation between the droplet/stabilizer size ratio and droplet shape: when the droplet/plate size ratios are >2, droplets with near-spherical shapes are formed; when the size ratios are between 1 and 2, droplets with polyhedral shapes (e.g., hexahedral and tetrahedral shapes) are formed; and when the size ratios are <1, sandwich-shaped droplets are formed. Droplets with similar structures tended to form if the droplet/plate size ratios were close, even though the sizes of the plate and droplet were different.