Dynamic structure factor and mutual diffusion

Studies of the motions of interacting colloids have focused on four topics, namely (i) the leading concentration dependence of Dm, (u) wave-vector dependence of Dm and correlation with other variables, (iii) detailed form of the temporal dependence of S(, t) in concentrated suspensions, and (iv) more extended descriptions from videomicroscopy of the statistics of particle motion. 

At elevated concentrations, light-scattering spectra of solutions of colloidal spheres become multimodal. Correspondingly, as required by Doob s theorem, particle motions cease to be described by a Gaussian random Markoff process. Segre, et al. report t), as obtained using a two-color, two-detector homo- 

Videomicroscopy offers possibilities that other techniques do not, such as the ability to visualize three-dimensional clusters in which cluster membership is determined by the particle dynamic properties, e.g., whether the particles are fast- or slow-moving(33). Videomicroscopy also allows measurement of quantities not directly accessible from other techniques, such as the van Hove self- and distinct distribution functions (x, t) and Gj(x, t) of the particle displacements. The Gs(x, t) gives the likelihood that a particle will have a displacements during a time t Gd(x, t) gives the likelihood that if one particle is at the origin at time 0 then a different particle will be at s at time t. A dilute bidisperse system in which particles of two different sizes all perform independent Brownian motion would have d.Gs(x, t) that was a sum of two Gaussians, a field correlation function t) 

What sorts of information have actually been obtained on colloid solutions using 

The VH scattered field is determined by the position and orientation of the scattering molecules, leading to a field correlation function given by Degiorgio, etal. as(lO) 

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