Self-consistent field modeling of adsorption from polymer/surfactant mixtures

Area of Science:

• Surface Chemistry
• Colloid Science
• Computational Modeling

Background:

• Nonionic surfactants and poly(ethylene oxide) (PEO) are widely used in formulations.
• Their adsorption behavior on inorganic surfaces like silica is complex and influenced by solution conditions.
• Understanding competitive adsorption is key to optimizing product performance.

Purpose of the Study:

• To develop a self-consistent field model for competitive adsorption of nonionic surfactants and PEO on silica.
• To investigate the influence of pH and ionic strength on adsorption.
• To predict adsorption isotherms and identify conditions for selective adsorption.

Main Methods:

• Development of a self-consistent field (SCF) model.
• Explicit inclusion of pH and ionic strength effects on surface charge and solvent quality.
• Calculation of bulk parameters like polymer coil size and surfactant critical micelle concentration (CMC).

Main Results:

• The model successfully predicts adsorption behavior and isotherms for polymers and surfactants.
• It identifies a critical surfactant adsorption concentration (CSAC) that dictates selective adsorption.
• Conditions were found where CMC < CSAC, preventing surfactant adsorption.

Conclusions:

• The developed SCF model provides insights into the competitive adsorption of surfactants and PEO on silica.
• The model explains many, but not all, experimental trends, highlighting areas for future refinement.
• This work advances the understanding of surface interactions in complex fluid systems.