Non-Equilibrium Mass Exchange in AOT Reverse Micelles

Area of Science:

• Physical Chemistry
• Supramolecular Chemistry
• Materials Science

Background:

• Reverse micelles (RMs) are self-assembled aggregates of surfactants in nonpolar solvents.
• Sodium bis(2-ethylhexyl)sulfosuccinate (AOT) in isooctane forms RMs with a narrow size distribution.
• The equilibrium size of RMs is primarily determined by their water loading ratio.

Purpose of the Study:

• To investigate the mechanisms by which RMs achieve their equilibrium size distribution.
• To differentiate between component diffusion and fusion-fission as RM size-regulating processes.
• To elucidate the role of molecular interactions in RM size dynamics.

Main Methods:

• All-atom molecular dynamics (MD) simulations were employed.
• A 24-microsecond simulation was conducted on a system containing two RMs of different sizes.
• Analysis focused on the movement of water and surfactant molecules (AOT) and RM fusion/fission events.

Main Results:

• Water was observed to transfer from smaller RMs to larger RMs, adjusting their sizes towards equilibrium.
• Changes in the number of AOT molecules per RM occurred exclusively through fusion and fission events.
• The observed behaviors were influenced by electrostatic interactions of sodium AOT and water's dielectric properties.

Conclusions:

• Water diffusion is a primary mechanism for adjusting RM size.
• RM fusion and fission are essential for modifying the surfactant composition and achieving overall system equilibrium.
• Electrostatic and dielectric effects play a crucial role in driving RM size dynamics.