  Micrometer sized alkane-in-water emulsion drops, stabilized by appropriate
long-chain surfactants, spontaneously break symmetry upon cooling and transform
consecutively into series of regular shapes (Denkov et al., Nature 2015, 528,
392). Two mechanisms were proposed to explain this phenomenon of drop
"self-shaping". One of these mechanisms assumes that thin layers of plastic
rotator phase form at the drop surface around the freezing temperature of the
oil. This mechanism has been supported by several indirect experimental
findings but direct structural characterization has not been reported so far.
We combine small- and wide-angle X-ray scattering (SAXS/WAXS) with optical
microscopy and DSC measurements of self-shaping drops in emulsions. In the
emulsions exhibiting drop self-shaping, the scattering spectra reveal the
formation of intermediate, metastable rotator phases in the alkane drops before
their crystallization. In addition, shells of rotator phase were observed to
form in hexadecane drops, stabilized by C16EO10 surfactant. This rotator phase
melts at ca. 16.6 {\deg}C which is significantly lower than the melting
temperature of crystalline hexadecane, 18 {\deg}C. The scattering results are
in a very good agreement with the complementary optical observations and DSC
measurements.
