Intensity fluctuation spectroscopy of charged Brownian particles: the coherent scattering function

Measurements are presented, which span wide ranges of scattering vector K and delay time tau , of the coherent intermediate scattering function F(K, tau ) for a dispersion of strongly-interacting charged Brownian particles (radius approximately 250 AA). Emphasis is on the long-time decay of F(K, tau ), i.e. for tau >> tau 1 , where tau 1 ( approximately 10 -4 s) is the particle's 'collision time'. D L , the diffusion coefficient describing this long-time decay, was found to be several times smaller than D 0 , the free-particle diffusion coefficient, and to be only weakly dependent on K. For K>K max , the position of the main peak in the particle structure factor S(K), F(K, tau ) approximately=F S (K, tau ), the self-scattering function which describes single-particle motions.