  We combine experiments and simulations to study the link between criticality
and gelation in sticky spheres. We employ confocal microscopy to image
colloid-polymer mixtures, and Monte Carlo simulations of the square-well (SW)
potential as a reference model. To this end, we map our experimental samples
onto the SW model. We find excellent structural agreement between experiments
and simulations, both for locally favored structures at the single particle
level and large-scale fluctuations at criticality. We follow in detail the
rapid structural change of the critical fluid when approaching the gas-liquid
binodal and highlight the role of critical density fluctuations for this
structural crossover. Our results link the arrested spinodal decomposition to
long-lived energetically favored structures, which grow even away from the
binodal due to the critical scaling of the bulk correlation length and static
susceptibility.
