Concentration fluctuations in binary mixtures of model polar fluids

We present calculations of the mean square concentration fluctuations, S_α(0), for binary mixtures of model polar fluids. The assumed pair interactions are taken to be of the forms of a hard core plus either dipole-dipole, quadrupole-quadrupole or dipole- quadrupole terms. The calculations are carried out within a mean field approximation. We have considered in some detail the interplay between size differences and the difference in the strength and range of the potentials in deciding how S_α(0) deviates from the ideal behaviour.