2-COLOR DYNAMIC LIGHT-SCATTERING

The design, alignment and operation of improved two-colour dynamic light scattering equipment which effectively suppresses multiple scattering and allows the study of the Brownian dynamics of optically turbid samples is described. The technique operates by cross-correlating scattered light of two different colours. With the appropriate scattering geometry, only singly scattered light contributes to the time-dependent part of the measured intensity cross-correlation function thus allowing straightforward interpretation of the data. To demonstrate the performance of the instrument we have studied various colloidal suspensions. Although dilute enough that free diffusion of the particles can be assumed, the samples ranged from quite transparent to distinctly turbid. We have confirmed that the measured cross-correlation functions accurately reflect only single scattering even in the presence of strong multiple scattering.