Attractive emulsions near the colloidal glass transition are investigated by rheometry and optical microscopy under shear. We find that (i) the apparent viscosity $\eta$ drops with increasing shear rate, then remains approximately constant in a range of shear rates, then continues to decay; (ii) the first normal stress difference $N_1$ transitions sharply from nearly zero to negative in the region of constant shear viscosity; and (iii) correspondingly, cylindrical flocs form, align along the vorticity, and undergo a log-rolling movement. An analysis of the interplay between steric constraints, attractive forces, and composition explains this behavior, which seems universal to several other complex systems.

• Received 13 June 2003

DOI:https://doi.org/10.1103/PhysRevLett.92.058303