  Effective colloid-colloid interactions can be tailored through the addition
of a complex cosolute. Here we investigate the case of a cosolute made by
self-assembling patchy particles. Depending on the valence, these particles can
form either polymer chains or branched structures. We numerically calculate the
effective potential $V_{eff}$ between two colloids immersed in a suspension of
reversible patchy particles, exploring a wide region of the cosolute phase
diagram and the role of valence. In addition to well-known excluded volume and
depletion effects, we find that, under appropriate conditions, $V_{eff}$ is
completely attractive but shows an oscillatory character. In the case of
polymerizing cosolute, this results from the fact that chains are efficiently
confined by the colloids through the onset of local order. This argument is
then generalized to the case of particles with higher valence, under the
condition that they are still able to maintain a fully bonded organization upon
confinement. The resulting effective potentials are relevant for understanding
the behavior of complex mixtures in crowded environments, but may also be
exploited for tuning colloidal self-assembly at preferred target distances in
order to build desired superstructures.
