Freezing-induced topological transition of double-emulsion

Area of Science:

• Colloid and Interface Science
• Materials Science
• Physical Chemistry

Background:

• Complex liquids like emulsions are vital in nature and industry.
• Understanding their phase transitions, such as solidification, is crucial.
• Hierarchical emulsions, like water-in-oil-in-water (W/O/W), present unique solidification behaviors.

Purpose of the Study:

• To investigate the solidification process of W/O/W double emulsions.
• To identify and characterize any topological transitions during freezing.
• To elucidate the mechanism behind the observed transition and identify critical parameters.

Main Methods:

• Preparation and manipulation of W/O/W double emulsions.
• Controlled freezing experiments.
• High-speed imaging to capture dynamic processes.
• Microscopy to analyze droplet morphology and size.

Main Results:

• Solidification of W/O/W emulsions can induce a topological transition.
• Observed transition from W/O/W to O/W (oil-in-water) single emulsion configuration.
• Inner water droplets are expelled from oil droplets during this transition.
• A critical inner drop size (R_in,crit ≈ 19 μm) was identified below which the transition is suppressed.

Conclusions:

• The freezing of the outer oil layer from the outside in creates tension, destabilizing the W/O/W structure.
• The topological transition is a result of this induced tension and subsequent expulsion of the inner water core.
• The stability of the W/O/W emulsion below the critical inner drop size is attributed to reduced interfacial stress during freezing.