A comprehensive methodology to study double emulsion stability

Hypothesis: The stability of emulsions requires the fast formation of viscoelastic interfaces between water and oil phases. In double emulsions, two surfactant types (hydrophilic and lipophilic) are present and two interfacial films are involved. Understanding cooperative adsorption of these surfactants and its implication on properties of water/oil/water interfacial films will enable replacing the empirical methodologies used in designing double emulsion systems with a knowledge-based approach. Experiments and model: The distribution of surfactants between the water/oil interfaces was investigated using single droplet diffusion experiments and simulation of equilibrium surfactant density profiles. The stability of the interfaces against coalescence was characterized by dye transport in a leach cell and coalescence time of single droplets in a model experiment. The conformation of the surfactants at an interface was then examined via surface rheology, sum frequency generation spectroscopy, and dissipative particle dynamics simulation. Findings: Two selected hydrophilic surfactants combined with a lipophilic surfactant induce very differ-ent properties at water/oil interfaces and different dye release behaviour from their corresponding dou-ble emulsions. Competitive adsorption of sodium dodecyl sulfate and lipophilic surfactant results in the improvement of encapsulation efficiency, elasticity of the interface, and resistance against coalescence due to the intercalation of surfactant alkyl chains into the oil chains. (c) 2022 Elsevier Inc. All rights reserved.

Automated summary

The stability of double emulsions depends on the rapid formation of viscoelastic interfaces between water and oil phases. Cooperative adsorption of hydrophilic and lipophilic surfactants and its impact on the properties of water/oil/water interfacial films were studied to replace empirical methodologies in designing double emulsion systems. Experiments and simulations were conducted to investigate surfactant distribution, stability against coalescence, and surfactant conformation at the interface. It was found that the competitive adsorption of sodium dodecyl sulfate and lipophilic surfactant resulted in improved encapsulation efficiency, interface elasticity, and resistance against coalescence.