Abstract
Soft colloids are increasingly used as model systems to address fundamental issues such as crystallisation and the glass and jamming transitions. Among the available classes of soft colloids, microgels are emerging as the gold standard. Since their great internal complexity makes their theoretical characterization very hard, microgels are commonly modelled, at least in the small-deformation regime, within the simple framework of linear elasticity theory. Here we show that there exist conditions where its range of validity can be greatly extended, providing strong numerical evidence that microgels adsorbed at an interface follow the two-dimensional Hertzian theory, and hence behave like 2D elastic particles, up to very large deformations, in stark contrast to what found in bulk conditions. We are also able to estimate the Young's modulus of the individual particles and, by comparing it with its counterpart in bulk conditions, we demonstrate a significant stiffening of the polymer network at the interface. Finally, by analyzing dynamical properties, we predict multiple reentrant phenomena: by a continuous increase of particle density, microgels first arrest and then re-fluidify due to the high penetrability of their extended coronas. We observe this anomalous behavior in a range of experimentally accessible conditions for small and loosely crosslinked microgels. The present work thus establishes microgels at interfaces as a new model system for fundamental investigations, paving the way for the experimental synthesis and research on unique high-density liquidlike states. In addition, these results can guide the development of novel assembly and patterning strategies on surfaces and the design of novel materials with desired interfacial behavior.
Highlights
Mesoscopic assemblies of colloids and nanoparticles display features that depend critically on the microscopic details of the building blocks, e.g., composition, size, and shape, as well as on the specific macroscopic physical conditions such as the thermodynamic control parameters
We show that there exist conditions where its range of validity can be greatly extended, providing strong numerical evidence that microgels adsorbed at an interface follow the two-dimensional Hertzian theory, and behave like 2D elastic particles, up to very large deformations, in stark contrast to what found in bulk conditions
In this work we provide the first numerical estimate of the two-body effective interaction potential of microgel particles adsorbed at an interface
Summary
Mesoscopic assemblies of colloids and nanoparticles display features that depend critically on the microscopic details of the building blocks, e.g., composition, size, and shape, as well as on the specific macroscopic physical conditions such as the thermodynamic control parameters. If a system is made of rigid building blocks that interact only through excluded volume interactions, it can be approximately mapped to a hardsphere system, and its behavior can be investigated through packing models. These approaches have been used for a long time to successfully answer fundamental questions in physics and material science whenever simple constituent units are involved [2]
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