Stability of Nonaqueous Emulsions

Area of Science:

• Colloid and Surface Science
• Physical Chemistry

Background:

• Nonaqueous emulsions are crucial in various industrial applications.
• Understanding factors influencing their stability is essential for formulation development.

Purpose of the Study:

• To investigate the stability of oil-in-nonaqueous polar liquid emulsions.
• To identify key factors governing the emulsifying power of solvents and surfactant performance.

Main Methods:

• Examined emulsion stability using commercially available nonionic surfactants in various polar solvents.
• Assessed the impact of solvent properties (polarity, hydrogen bonding), surfactant molecular size, and oil phase additives on emulsion longevity.
• Investigated Ostwald ripening and droplet coalescence as destabilization mechanisms.

Main Results:

• Stable nonaqueous emulsions were exclusively formed in formamide and dimethylsulfoxide.
• Hydrogen bonding capacity of the solvent, rather than mere polarity, determined emulsifying power.
• Ostwald ripening significantly impacted stability, more so than in aqueous systems.
• Adding a low-solubility oil to the oil phase inhibited Ostwald ripening.
• Larger surfactant molecules, such as triblock copolymers, prevented droplet coalescence.

Conclusions:

• Formamide and dimethylsulfoxide are suitable solvents for stable nonaqueous emulsions due to their hydrogen bonding capabilities.
• Emulsion stability is enhanced by controlling Ostwald ripening and droplet coalescence through appropriate solvent selection, oil phase modification, and surfactant design.