  The combination of soft responsive particles, such as microgels, with
nanoparticles (NPs) yields highly versatile complexes of great potential for
applications, from ad-hoc plasmonic sensors to controlled protocols for loading
and release. However, the assembly process between these microscale networks
and the co-dispersed nano-objects has not been investigated so far at the
microscopic level, preempting the possibility of designing such hybrid
complexes a priori. In this work, we combine state-of-the-art numerical
simulations with experiments, to elucidate the fundamental mechanisms taking
place when microgels-NPs assembly is controlled by electrostatic interactions.
We find a general behavior where, by increasing the number of interacting NPs,
the microgel deswells up to a minimum size, after which a plateau behavior
occurs. This occurs either when NPs are mainly adsorbed to the microgel corona
via the folding of the more external chains, or when NPs penetrate inside the
microgel, thereby inducing a collective reorganization of the polymer network.
By varying microgel properties, such as fraction of crosslinkers or charge, as
well as NPs size and charge, we further show that the microgel deswelling
curves can be rescaled onto a single master curve, for both experiments and
simulations, demonstrating that the process is entirely controlled by the
charge of the whole microgel-NPs complex. Our results thus have a direct
relevance in fundamental materials science and offer novel tools to tailor the
nanofabrication of hybrid devices of technological interest.
