Elastic response of binary hard-sphere fluids

We derive expressions for the high-frequency, wave-number-dependent elastic constants of a binary hard-sphere fluid and employ Monte Carlo computer simulation to evaluate these constants in order to highlight the impact of composition and relative sphere diameter on the elastic response of this system. It is found that the elastic constant c(11)(k) exhibits oscillatory behavior as a function of k whereas the high-frequency shear modulus, for example, does not. This behavior is shown to be dictated by the angular dependence (in (k) over right arrow space) of derivatives of the interatomic force at contact. The results are related to recent measurements of the compressibility of colloidal fluids in laser trapping experiments.