Coalescence Frequency in O/W Emulsions: Comparisons of Experiments with Models

Area of Science:

• Colloid and Surface Science
• Materials Science
• Physical Chemistry

Background:

• Emulsion stability is crucial in many industrial applications.
• Understanding droplet coalescence is key to predicting emulsion lifespan.
• Surfactant properties significantly influence emulsion behavior.

Purpose of the Study:

• To investigate the coalescence dynamics of oil-in-water emulsions.
• To determine the factors controlling the rate of phase separation.
• To compare the coalescence behavior of emulsions stabilized by ionic and nonionic surfactants.

Main Methods:

• Preparation of oil-in-water emulsions using alkane oils and various surfactants (cationic, nonionic, polymeric).
• Observation of phase separation, creaming, and coalescence under gravity.
• Application of the Dinh et al. model to relate coalescence time to activation energy.
• Surface tension measurements and Gibbs adsorption equation calculations to determine surface compression elastic modulus.

Main Results:

• Phase separation occurs in two distinct steps: initial creaming followed by rapid coalescence, and later dramatic coalescence.
• Complete phase separation time (Tc) correlates with coalescence frequency and activation energy.
• Coalescence is a thermally activated process controlled by the surface compression elastic modulus.
• Ionic surfactants exhibit a two-step film rupture process, unlike nonionic surfactants.

Conclusions:

• The coalescence of stable oil-in-water emulsions is a thermally activated process.
• The surface compression elastic modulus is a critical parameter controlling emulsion coalescence.
• Differences in coalescence behavior between ionic and nonionic systems are attributed to distinct film rupture mechanisms.