Computer simulation of diffusing-wave spectroscopy of colloidal dispersions and particle gels

A computational approach has been developed to model diffusing wave-spectro scopy (DWS) behavior in colloidal systems. This model has been applied to t he study of both colloidal dispersions and particle gels. The individual pa rticle dynamics are computed from a Brownian dynamics simulation. Subsequen tly, a large number of photon paths through the system are generated. These paths, in combination with the mean-square displacements of the particles obtained from the Brownian dynamics simulations, are used to calculate the temporal autocorrelation function g((1))(t). The simulations reproduce the effect of the system thickness on g((1))(t) for a stable colloidal dispersi on as found experimentally, as well as the effect of the composition of a b imodal dispersion. Simulations of particle gels show how the gelation proce ss influences the correlation function. These simulations reproduce the pro found changes in the correlation function seen experimentally during the ge lation process and demonstrate that such effects are primarily due to chang es in the particle dynamics rather than in the large-scale topology of the developing network.