Measurement of coagulation rate constants using number-fluctuation spectroscopy

Abstract

The fluctuations in number and scattering power of particles in a small volume have been measured via the moments of the detected intensity distribution. Under the approximation that a k-fold aggregate scatters, on average, k times the intensity of a singlet, the evolution of the intensity moments during Smoluchowski aggregation are related to the aggregation half-life. In particular, the second moment increases linearly with time and the rate of increase leads to an estimate of coagulation half-life. Choosing the ‘angle of no change’(the angle where the mean scattered intensity remains constant during coagulation) as the scattering angle ensures the validity of the approximations. Measurements made on rapidly coagulating polystyrene latex samples are compared with theory and with results obtained using other techniques.