Bulk viscosity universality and scaling function near the binary liquid consolute point.

The hydrodynamical equations and the notion of a frequency dependent complex specific heat near the critical point of binary liquids are used to obtain an expression for the low-frequency bulk viscosity. In this way the interrelations between different theoretical models, treating the critical sound attenuation from either a specific heat or a bulk viscosity approach, are made evident. The general structure of the bulk viscosity relation agrees with that of Onuki [Phys. Rev. E 55, 403 (1997)] but a universal number emerges only if a normalization to the critical point value is done.