Structural Interpretations of Static Light Scattering Patterns of Fractal Aggregates

Area of Science:

• Colloid and Surface Chemistry
• Light Scattering Physics
• Materials Science

Background:

• Aggregate size and structure are crucial for predicting particle behavior.
• Traditional light scattering methods (Rayleigh approximation) fail for large primary particles.
• Multiple scattering and size polydispersity complicate aggregate analysis.

Purpose of the Study:

• To experimentally validate a new theoretical approach for aggregate structure and size determination.
• To address challenges posed by multiple scattering in light scattering measurements.
• To correlate optical properties with structural changes during aggregation.

Main Methods:

• Utilized Mie scattering theory, accounting for multiple scattering effects.
• Studied chemically controlled aggregation of 0.8-µm latex particles.
• Analyzed scattered intensity to extract structural and size information.

Main Results:

• Polydispersity effects hinder direct interpretation of the Structure factor S(q).
• Decreasing optical contrast correlates with aggregate structural changes, independent of polydispersity.
• A strong correlation was found between fractal dimension (D(f)) and mean optical contrast at large scattering angles.

Conclusions:

• The new theoretical approach successfully extracts aggregate structure and size information.
• Optical contrast serves as a reliable indicator of structural evolution in aggregates.
• The Form factor (F(q)) and Structure factor (S(q)) can describe aggregate structure and size polydispersity, even with multiple scattering.