Effect Of Shear Flows On Critical Fluctuations In Fluids

A shear flow distorts the equal time correlation functions <∥mk∥2> for a fluid system with order parameter m, just above a critical point. We analyse this effect here for the case where m is not a conserved quantity : physical examples may be found with the transition smectic Cc → smectic A or possibly smectic A→ nematic. We find an important, anisotropic, reduction of fluctuations of wave vector k where kζ > 1 provided that ST > 1 (where ζ is the correlation length and τ the relaxation time of the uniform mode).