The determination of the mean and standard deviation of the size distribution of a colloidal suspension of submicron particles using the Fiber Optic Doppler Anemometer, FODA

Laser light-scattering measurements of the Brownian motion of a colloidal suspension of silica particles, Syton, by means of the Fiber Optic Doppler Anemometer (FODA) were used to determine the mean and standard deviation of the particle size distribution. Measurements over a wide range of concentrations from undiluted Syton to 0.049% Syton solution showed a consistent power spectrum of scattered light amplitude fluctuations. Using a modified Lorentzian model for the power spectrum, a computer least-squares curve fit and a graphical method were used to calculate the mean and standard deviation of particle radius. The results were consistent for all concentrations of Syton, verifying the versatility of the FODA and the accuracy of the modified Lorentzian model. The mean and standard deviation of particle radius in Syton were found to be 46.5 and 20.8 nm, respectively. It was found that clumping in undiluted Syton caused an apparent increase in the mean and standard deviation of the particle size distribution, as compared with all of the other dilutions where clumping did not occur.