  Travelling waves of densities of binary fluid mixtures are investigated near
a critical point. The free energy is considered in a non-local form taking
account of the density gradients. The equations of motions are applied to a
universal form of the free energy near critical conditions and can be
integrated by a rescaling process where the binary mixture is similar to a
single fluid. Nevertheless, density solution profiles obtained are not
necessarily monotonic. As indicated in Appendix, the results might be extended
to other topics like finance or biology.
