Macroscopic, mesostructured cationic surfactant/neutral polymer films: structure and cross-linking

Area of Science:

• Materials Science
• Polymer Chemistry
• Surface Science

Background:

• Mesostructured films of surfactants and polyethylenimines self-assemble at the air/water interface.
• These films are unusually thick (micrometers) and robust.
• Existing films are difficult to remove from the liquid surface without structural damage.

Purpose of the Study:

• To investigate the cross-linking of self-assembled polymer-surfactant films.
• To determine if cross-linking allows removal as solid membranes.
• To characterize the structural integrity and properties of the resulting membranes.

Main Methods:

• Surface sensitive techniques for film examination.
• Cross-linking of films.
• Grazing incidence X-ray diffraction (GID) for structural analysis.
• Investigation of polymer molecular weight and pH effects.

Main Results:

• Cross-linking enables removal of films as solid, mesostructured polymer-surfactant membranes.
• Cross-linking preserves metastable mesostructures and nanoscale order upon drying.
• GID revealed 2D-hexagonal phase crystallites of surfactant micelles within the polymer matrix.
• Polymer molecular weight significantly impacts film thickness and order; higher MW leads to thicker, less ordered films.
• Increased pH generally increases film thickness and improves order in low MW films.

Conclusions:

• Cross-linking is a viable method to create stable, solid mesostructured polymer-surfactant membranes.
• The developed membranes retain nanoscale order and show potential for various applications.
• A model is proposed relating film formation, phase separation, and ordering to experimental parameters like polymer MW and pH.