  The rheological behavior of colloidal dispersions is of paramount importance
in a wide range of applications, including construction materials, energy
storage systems and food industry products. These dispersions consistently
exhibit non-Newtonian behaviors, a consequence of intricate interplays
involving colloids morphology, volume fraction, and inter-particle forces.
Understanding how colloids structure under flow remains a challenge,
particularly in the presence of attractive forces leading to clusters
formation. In this study, we adopt a synergistic approach, combining rheology
with ultra small-angle X-ray scattering (USAXS), to probe the flow-induced
structural transformations of attractive carbon black (CB) dispersions and
their effects on the viscosity. Our key findings can be summarized as follow.
First, testing different CB volume fractions, in the high shear rate
hydrodynamic regime, CB particles aggregate to form fractal clusters. Their
size conforms to a power law of the shear rate, $\xi_c \propto
\dot{\gamma}^{-m}$, with $m\simeq 0.5$. Second, drawing insights from the
fractal structure of clusters, we compute an effective volume fraction
$\phi_{\mathrm{eff}}$ and find that microstructural models adeptly account for
the hydrodynamic stress contributions. We identify a critical shear rate
$\dot{\gamma^*}$ and a critical volume fraction $\phi_{\mathrm{eff}}^{*}$, at
which the clusters percolate to form a dynamical network.
