Chemically Tuning Attractive and Repulsive Interactions between Solubilizing Oil Droplets.

Area of Science:

• Colloid and Surface Science
• Soft Matter Physics
• Emulsion Science

Background:

• Micellar solubilization in emulsions typically drives droplet repulsion via Marangoni flow.
• Active droplets, propelled by interfacial tension gradients, usually exhibit self-propulsion and pairwise repulsion.

Purpose of the Study:

• To investigate emulsions where solubilization leads to droplet attraction.
• To characterize how oil and surfactant properties influence interfacial tension and Marangoni flow in oil-in-water drops.

Main Methods:

• Systematic variation of oil chemical structure and nonionic surfactant structure.
• Analysis of surfactant concentration effects on interfacial tension and Marangoni flow.
• Identification of distinct regimes of droplet interaction (attraction, repulsion, inactivity).

Main Results:

• Demonstrated that specific solubilization processes can decrease interfacial tension, inducing droplet attraction.
• Identified three distinct regimes governing droplet dynamics: attraction, repulsion, and inactivity.
• Correlated oil and surfactant structures with observed interfacial tension changes and Marangoni flow patterns.

Conclusions:

• Solubilization processes can be tuned to control droplet interactions in emulsions, leading to attraction rather than repulsion.
• Findings provide fundamental insights into emulsion dynamics and chemotaxis of active droplets.
• Offers guidance on leveraging chemical parameters to engineer droplet behavior and interactions.