Three-dimensional confinement-related size changes to mixed-surfactant vesicles.

Area of Science:

• Colloid and Surface Science
• Materials Science
• Physical Chemistry

Background:

• Surfactant mesophases, such as vesicles, are crucial in various applications.
• Understanding how confinement affects these structures is key for optimizing their performance.
• Previous studies have explored confinement effects, but detailed investigations into 3D confinement on vesicle size are limited.

Purpose of the Study:

• To investigate the impact of three-dimensional confinement on the size and morphology of vesicular surfactant mesophases.
• To determine the relationship between confinement length scale and vesicle dimensions.
• To validate experimental findings with a thermodynamic model.

Main Methods:

• Utilized small-angle neutron scattering (SANS) to study vesicle structures.
• Created confined environments using packed polystyrene beads of varying sizes (0.1, 0.25, 1.5 microm).
• Analyzed SANS data using a core-shell model to confirm vesicle presence and size.

Main Results:

• Vesicles were confirmed as the dominant structure under confinement.
• The mean size of vesicles decreased significantly with reduced confinement length scale.
• Experimental data were well-supported by a thermodynamic model balancing enthalpy and entropy.

Conclusions:

• Three-dimensional confinement effectively reduces the size of surfactant vesicles.
• The observed size reduction is governed by thermodynamic principles related to curvature and free volume.
• Findings have implications for drug delivery, enhanced oil recovery, and micellar enhanced ultrafiltration.