Interfacial mechanisms in active emulsions.

Area of Science:

• Colloid and Surface Science
• Non-equilibrium Systems
• Soft Matter Physics

Background:

• Active emulsions, with self-propelled droplets, model biological collectives like phytoplankton and bacteria.
• They are crucial for studying non-equilibrium phenomena, rheology, pattern formation, and phase transitions.
• Fueling active emulsions often involves molecular processes affecting stabilizing surfactants.

Purpose of the Study:

• To outline and compare two distinct molecular reaction pathways for fueling active emulsions.
• To investigate the symmetry-breaking mechanisms and resulting locomotion in each pathway.
• To understand the influence of surfactant modification versus colloidal transfer on emulsion dynamics.

Main Methods:

• Comparison of two reaction types: chemical surfactant modification and surfactant transfer to a different colloidal state.
• Analysis of symmetry breaking mechanisms, distinguishing between linear and nonlinear instabilities.
• Evaluation of locomotion emergence based on the specific dissolution pathway.

Main Results:

• Chemical modification of surfactants leads to locomotion via standard linear instability and symmetry breaking.
• Surfactant transfer to a different colloidal state presents a more complex scenario.
• The dissolution pathway in the second case can result in intrinsically nonlinear instability or a complete lack of symmetry breaking and locomotion.

Conclusions:

• The method of fueling active emulsions significantly dictates their emergent behavior and locomotion.
• Chemical modification offers a predictable route to active emulsion dynamics through linear instability.
• Surfactant transfer pathways require careful consideration due to potential for complex nonlinear dynamics or failure to achieve locomotion.