Specific Surface Area by SAXS

SAXS measures the scattering arising from electron-density contrast between two phases. For biphasic systems (e.g., particles in solution, pores within solids), the high-q region of the scattering curve carries information about the total interfacial area between the phases.

From this analysis, SAXS provides:

• Specific surface area, expressed as interfacial area per unit mass (m²/g) or per unit volume (m²/cm³)
• Surface-to-volume ratio, derived from the Porod regime intensity decay
• Total scattering invariant, used to normalize the interfacial area and ensure quantitative accuracy
• Access to both open and closed pores, because the contrast-based signal originates from all interfaces, not only externally accessible ones

Specific surface determination typically relies on Porod analysis, which relates the slope of the high-q scattering to surface area, combined with accurate extrapolation of the data and normalization via the scattering invariant.

These approaches follow the methodologies formalized in ISO 20804:2022, the international standard governing SAXS determination of specific surface area in porous and particulate materials.

SAXS enables specific surface determination for a wide variety of two-phase materials, including:

• Colloidal dispersions and solutions, such as nanoparticle suspensions
• Dry powders and particulate materials
• Porous solids, including mesoporous or microporous media
• Granular or composite materials
• Nanostructured solids, such as catalysts or templated materials

Because SAXS requires minimal preparation and probes large sample volumes, it is ideally suited for native, undisturbed samples, including opaque or dense materials.

SAXS provides a robust, quantitative, and broadly applicable method for measuring interfacial area. Its strengths include:

These advantages make SAXS a powerful technique for understanding how nanoscale interfacial structure influences material performance, from catalysts and porous media to nanoparticles, composites, and energy-storage materials.