Drying of Aerogels with Supercritical Carbon Dioxide

Significance of the Topic

Supercritical carbon dioxide (SC-CO2) offers an eco-friendly, solvent-free approach to infuse additives into robust polymers such as polyimides. By overcoming the impermeability of cured polyimide films, SC-CO2 infusion enables the creation of advanced reflective coatings and functional materials for aerospace, electronics and other high-performance applications.

Objectives and Study Overview

This study demonstrates the use of SC-CO2 to introduce a silver-containing complex into fully cured BTDA-ODA polyimide films. The aim is to develop a rapid, one-step impregnation process that yields flexible, highly reflective films without toxic residues or high-temperature solvent processes.

Methodology and Instrumentation

The cured polyimide film is loaded with 10 wt % silver(I) hexafluoro-acetylacetonate complex and placed in a 10 mL high-pressure vessel. SC-CO2 is pressurized to 5 000 psi at 110 °C for 120 minutes to dissolve and infuse the additive. After infusion, the cell is cooled to ambient temperature, depressurized, and the film is removed and post-cured at 300 °C.

Used Instrumentation

• Applied Separations Spe-ed™ SFE-2 or Helix supercritical fluid extractor
• Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) for silver distribution analysis
• Thermogravimetric analysis (TGA) for optical reflectivity assessment

Main Results and Discussion

The SC-CO2 process achieved uniform silver dispersion within the polyimide matrix and on its surface. SEM and TEM confirmed nano-scale silver domains, while TGA-derived reflectivity measurements indicated a marked increase in surface reflectivity. The films retained their mechanical flexibility and showed no evidence of residual solvent contaminants.

Benefits and Practical Applications

• Eliminates toxic liquid solvents and high-temperature steps
• Reduces processing time to a single infusion cycle
• Produces flexible, reflective films suitable for aerospace mirrors, electronic shielding and decorative finishes
• Allows CO2 recycling for large-scale, cost-effective production

Future Trends and Opportunities

Advances may include infusion of a broader range of metallic and oxide additives for multifunctional coatings, integration with roll-to-roll SC-CO2 processing for continuous production, and in-situ monitoring of additive distribution. Hybrid approaches coupling SC-CO2 with plasma or UV treatments could further tailor surface properties.

Conclusion

Supercritical CO2 permeation provides a fast, safe and sustainable route to embed silver additives into polyimide films, yielding highly reflective, flexible materials without solvent residues. This method holds promise for scalable manufacturing of advanced polymer coatings.

References

Boggess, R. and Taylor, L. Infusion of Silver into Polyimides by the Use of Supercritical Carbon Dioxide. J. Appl. Polym. Sci., 64, 1309 (1997).
Nazem, N.; Taylor, L.; Rubira, A. Supercritical Fluid Infusion of a Silver-Containing Compound into Poly(Ether Ether Ketone) for the Purpose of Making Reflective Films.