Nonionic Fluorinated Surfactant Removal from Mesoporous Film Using sc-CO₂

Area of Science:

• Materials Science
• Nanotechnology
• Physical Chemistry

Background:

• Thin films are crucial in various technological applications.
• Controlling nanostructure in silica films is essential for tailored properties.
• Surfactant templating offers a route to ordered porous materials.

Purpose of the Study:

• To identify the optimal composition for a 2D rectangular crystalline phase in surfactant-templated silica films.
• To investigate the effectiveness of supercritical carbon dioxide (sc-CO2) for template removal.
• To characterize the structural integrity of the silica films after template removal.

Main Methods:

• Self-assembly of silica thin films via dip-coating using a partially fluorinated surfactant (R8F(EO)9).
• In situ X-ray reflectivity (XRR) and grazing incidence small-angle X-ray scattering (GISAXS) under varying sc-CO2 pressures (0-100 bar at 34 °C).
• Analysis of structural changes and template removal efficiency.

Main Results:

• A 2D rectangular structure was formed at a specific molar ratio (R8F(EO)9/Si = 0.1).
• Supercritical carbon dioxide successfully removed the R8F(EO)9 surfactant.
• The 2D rectangular structure was maintained after template removal and depressurization.
• High stability of the final silica film attributed to thick walls and small pore size.

Conclusions:

• The study successfully fabricated ordered 2D rectangular silica thin films.
• sc-CO2 is an effective and structure-preserving method for template removal.
• The resulting silica films exhibit high stability, suitable for advanced applications.