Correlation of Changes in Optical Properties of Soot Particles Synthesized in a Premixed Flame with Increasing Mean Particle Size

The data on the optical band gap and dispersion coefficient of soot particles as functions of their primary size are presented. Optical properties of particles are obtained by interpretating the data on the spectral absorbance measured by the laser extinction method at wavelengths of 405-850 nm. Premixed flame is used as a reactor for synthesizing soot particles. It is shown that as the soot primary particle size increases from 11 to 20 nm, the optical band gap decreases from 0.8 to 0.02-0.05 eV, and the dispersion coefficient decreases from 1.8 to 1. The cause of changes in optical properties is soot particle growth from the so-called "young" to "mature" ones accompanied by changes in their structure, i.e., an increase in their degree of graphitization. The internal structure of particles during their growth approaches to the graphite structure. It is found that an additional parameter affecting changes in optical properties is the type of fuel used in the synthesis of soot particles.