Equilibrium state model for surfactants in oils: Colloidal assembly and adsorption

Area of Science:

• Colloid and Surface Science
• Physical Chemistry
• Materials Science

Background:

• Colloidal systems in apolar solvents are crucial in various applications, yet their aggregation and adsorption behavior is complex.
• Existing models often struggle to accurately capture the step-wise aggregation and surface phenomena of surfactants in oils.

Purpose of the Study:

• To develop and validate an equilibrium state model for colloidal assembly and adsorption in apolar solvents.
• To investigate the influence of surfactant properties and solvent environment on aggregation and adsorption behavior.
• To provide a computationally feasible tool for predicting surfactant performance in oil-based systems.

Main Methods:

• Development of an equilibrium state model incorporating monomer exchange and surface crowding effects.
• Utilized scaled particle theory (SPT) to model surface phenomena.
• Validated the model against molecular modeling data for oleic acid and monoolein, and experimental adsorption isotherms for phospholipids.

Main Results:

• The model accurately reproduces chemically specific aggregate distributions in both bulk and surface phases.
• A biased state model, accounting for distinct dimer formation, significantly improved accuracy.
• Model fits to phospholipid adsorption data revealed monolayer or aggregate adsorption structures, dependent on head group charge.

Conclusions:

• The presented model offers an accessible and computationally efficient method for estimating colloidal assembly and adsorption in oil environments.
• It enables the assessment of surfactant aggregation propensity and adsorption energetics.
• The model demonstrates broad applicability across different surfactant types and experimental conditions.