Toward a unified description of the electrostatic assembly of microgels and nanoparticles

TL;DR

This study combines experiments and simulations to understand how electrostatic interactions govern the assembly of microgels and nanoparticles, revealing a universal deswelling behavior that can be scaled onto a master curve.

Contribution

It provides a unified microscopic description of microgel-NP assembly driven by electrostatics, integrating experimental and simulation data for the first time.

Findings

Microgel deswelling reaches a minimum size with increasing NPs.

Deswelling behavior can be scaled onto a single master curve.

Assembly mechanisms include surface adsorption and internal penetration of NPs.

Abstract

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.