Measurement of particle diffusion coefficients with high accuracy by dynamic light scattering

Abstract

We present a novel optical scattering cell for the measurement of particle diffusion coefficients by dynamic light scattering, which may be utilised for particle size analysis and viscosity measurements. A major feature of the cell is that it allows measurements without knowledge of the refractive index of the dispersing liquid, which facilitates viscosity measurements over an extended range of temperature, where refractive indexes are often not found tabulated. This improvement is achieved by the use of a symmetrical set-up.

The light scattering system has been tested by measuring the diffusion coefficient of silica particles in water, where the results showed a total standard deviation of 0.5% including measurements at various angles of incidence. In order to prove the capability of the system for accurate viscosity measurements, n-heptane, where reliable reference values are available, has been investigated in a temperature range of 20°–80°C. The viscosities measured showed a maximum deviation of the mean from the reference values of below 1.0%.