Rotator phases in hexadecane emulsion drops revealed by X-ray synchrotron techniques

Area of Science:

• Colloid and surface science
• Materials science
• Physical chemistry

Background:

• Micrometer-sized alkane-in-water emulsion drops exhibit spontaneous shape changes upon cooling.
• This phenomenon, termed

Purpose of the Study:

• To provide direct structural evidence for the proposed mechanism of drop self-shaping involving rotator phases.
• To investigate the role of rotator phases in the self-shaping of alkane emulsion drops.

Main Methods:

• Combined small- and wide-angle X-ray scattering (SAXS/WAXS).
• Optical microscopy.
• Differential scanning calorimetry (DSC).

Main Results:

• Scattering spectra confirmed the formation of intermediate, metastable rotator phases in alkane drops before crystallization.
• Observed rotator phase shells in hexadecane drops stabilized by C16EO10 surfactant.
• The rotator phase melted at 16.6 °C, below the crystalline hexadecane melting point of 18 °C.

Conclusions:

• Directly observed rotator phase formation, supporting the hypothesis of thin rotator layers driving self-shaping.
• The findings align with indirect experimental evidence and complementary optical and thermal measurements.
• This study elucidates a key structural transition governing emulsion drop morphology changes.