Aim: This study aimed to investigate the influence of the preparation process and composition on the
microstructure of the O/W primary emulsions and the corresponding impact on the formation of oil-in-water-in-oil (O/W/O)
Objectives: Multiple emulsions were prepared by a two-step emulsification method and the microstructure was
characterized by the microscope.
Methods: The primary emulsion was prepared by four kinds of preparation methods, which including both high-energy and
low-energy emulsification, and then the primary emulsion was re-emulsified by stirring in the outer phase.
Result: Through the theoretical investigation and the corresponding verification experiments of the interfacial film, the
geometric reason for that the O/W/O multiple emulsion was relatively difficult to prepare has been found. The
microstructure of O/W particles was more obvious, and the particle size were smaller with the increase of the hydrophilic
emulsifier amount which was beneficial to the formation and stability of O/W/O structures. However, the excess emulsifier
existed in the water phase could interfere the stability of the W/O interface. Moreover, the viscosity of inner oil phase had a
large influence on the formation of O/W/O emulsion by affecting the particle size of the primary emulsion and the dynamic
equilibrium between the inner and outer oil phase.
Conclusion: It can be concluded that fine multiple emulsions formed when the particle size of the primary emulsion was
moderate since the large particles would breaking through the outer interface membrane and small particles would
combining with the outer oil phase due to the Ostwald ripening.