Internal fields of soot fractal aggregates

Area of Science:

• Physics
• Materials Science
• Nanotechnology

Background:

• Carbon soot aggregates exhibit complex fractal structures.
• The Rayleigh-Debye-Gans Approximation (RDGA) is often used to model light scattering from such aggregates.
• Understanding internal electric fields is crucial for accurate scattering predictions.

Purpose of the Study:

• To investigate the internal electric field of carbon soot fractal aggregates using the discrete dipole approximation (DDA).
• To compare DDA results with the RDGA for both fixed and random aggregate orientations.
• To elucidate the reasons for the observed agreement in far-field scattering despite internal field discrepancies.

Main Methods:

• Simulations using the discrete dipole approximation (DDA).
• Analysis of carbon soot fractal aggregates in fixed and random orientations.
• Comparison of DDA-calculated internal fields and scattered intensities with RDGA predictions.

Main Results:

• DDA simulations show internal electric field deviations up to ±50% compared to RDGA for fixed orientations.
• Despite internal field differences, far-field scattered intensity from aggregates agrees well with RDGA.
• Orientational averaging of random aggregates leads to agreement between DDA and RDGA scattering, exhibiting power-law behavior.

Conclusions:

• The fractal structure and orientational averaging of carbon soot aggregates are key to the experimental validity of the RDGA.
• Error cancellation in internal field estimations contributes to the accurate prediction of scattered intensity.
• The RDGA's validity for far-field scattering is maintained despite its limitations in describing internal fields for these structures.