The use of photon correlation spectroscopy for estimating the rate constant for doublet formation in an aggregating colloidal dispersion

Abstract An expression is derived relating the rate constant for doublet formation to the experimentally measured rate of change of the intensity-weighted mean particle radius, at early times, determined from photon correlation spectroscopy (PCS). The rate constant for doublet formation is proportional to a derived “optical factor” that is a function of particle size, scattering angle, and wavelength of light in the dispersing medium. The optical factor is calculated using form factors from Rayleigh-Debye theory and diffusion coefficients from Kirkwood-Riseman theory. Estimation of the rate constant for doublet formation using early-time PCS measurements suggests that particle concentrations no greater than 10 9 particles/cm 3 should be used.