  We use Molecular Dynamics combined with Dissipative Particle Dynamics to
construct a model of a binary mixture where the two species differ only in
their dynamic properties (friction coefficients). For an asymmetric mixture of
slow and fast particles we study the interdiffusion process. The relaxation of
the composition profile is investigated in terms of its Fourier coefficients.
While for weak asymmetry we observe Fickian behavior, a strongly asymmetric
system exhibits clear indications of anomalous diffusion, which occurs in a
crossover region between the Cases I (Fickian) and II (sharp front moving with
constant velocity), and is close to the Case II limit.
