Pickering water-in-oil emulsions stabilized by beeswax crystals: Design and stability

The aim of this study was to understand how beeswax can be used to stabilize water-in-oil emulsions and understand the impact of droplet volume fraction on stability. Pickering water-in-oil (W/O) emulsions were successfully designed using beeswax oleogels (4 wt%) as the sole stabilizer via a facile homogenization approach. The effects of beeswax crystals on the formation, stability, and structural organization of W/O emulsions (containing up to 70% v/v water) were systematically investigated. Oleogelation reduced the interfacial tension between oil and water from 21 ± 1 mN/m to 14 ± 1 mN/m, enabling beeswax crystals to stabilize emulsions without the need for synthetic surfactants. X-ray diffraction analysis revealed that beeswax crystals in oleogels exhibited a stable β’ polymorph with orthorhombic packing, maintaining a reduced long-chain spacing from 7.8 nm in pure beeswax to 6.3 nm, which contributed to the stabilization of Pickering W/O emulsions. The emulsions ranged in size (D32) from 8 to 16 μm depending upon the droplet volume fraction and showed no significant change over storage period of 6 weeks. Microscopic observations of the interface demonstrated that emulsion stability was achieved through the synergistic effects of both the Pickering stabilization and bulk network stabilization. This dual stabilization mechanism was further confirmed by thermal cycling experiments and in situ crystallization analysis at the interface as well as rheological measurements showing gel formation at higher volume fractions of droplets. Overall, these findings highlight the potential of beeswax to stabilise W/O emulsions for applications in food and allied soft matter industries.