MOBILITY VARIANCE DETERMINED FROM AC ELECTROPHORETIC LIGHT-SCATTERING

The homodyne correlation function for light scattered from an aqueous suspension of particles in a uniform oscillating electric field is calculated assuming the mobility varies from particle to particle. The correlation function has an exponential decay that is modulated at frequency omega/2-pi with amplitude (q.E/omega)2 <DELTA-mu-2>, where q is the scattering vector, E and omega/2-pi are the amplitude and frequency of the oscillating field, and <DELTA-mu-2> is the variance of the mobility of the particles. The variance can be determined by fitting the theoretical correlation function to homodyne photon autocorrelation measurements. This technique has the advantage of insensitivity to convection of the particles from heating by the applied electric field.