Structural Properties of Span 80/Tween 80 Reverse Micelles by Molecular Dynamics Simulations

Area of Science:

• Colloid and Surface Chemistry
• Materials Science
• Computational Chemistry

Background:

• Reverse micelles (RMs) in water-in-oil microemulsions are crucial for various applications.
• Understanding the self-assembly and structural properties of RMs is essential for optimizing their performance.
• Previous studies identified coexistence of large and small RMs in sorbitan monooleate (Span 80)/poly(oxyethylene) sorbitan monooleate (Tween 80) systems.

Purpose of the Study:

• To investigate the structural properties of Span 80/Tween 80 reverse micelles using molecular dynamics simulations.
• To elucidate the role of individual and mixed surfactants in RM formation and stability.
• To quantitatively describe the inner structure and molecular arrangement within RMs.

Main Methods:

• Molecular dynamics simulations employing a united-atom approach for surfactant and decane models.
• Simulation of self-assembly from initially homogeneous mixtures of surfactant, water, and decane.
• Analysis of RM shape dependence on surfactant composition and quantitative description of inner structures.

Main Results:

• Established the dependence of RM shape on the relative content of Span 80 and Tween 80.
• Quantitatively described the inner structure of individual (Span 80 or Tween 80) and mixed RMs.
• Observed Tween 80 molecules penetrating the water core, while Span 80 molecules localized on the RM surface.
• Identified hydrogen bonds between surface surfactant molecules as critical for RM formation.
• Analyzed water hydrogen bond density distribution, highlighting advantages of mixed surfactant systems.

Conclusions:

• The relative content of Span 80 and Tween 80 significantly influences RM shape.
• Mixed surfactant systems exhibit enhanced stability and structural organization compared to individual surfactants.
• Hydrogen bonding between surface-localized Span 80 molecules plays a key role in stabilizing the reverse micelle structure.
• The distinct localization of Tween 80 within the core and Span 80 on the surface contributes to the superior performance of mixed RMs.