Dottorato in MODELLI MATEMATICI PER L'INGEGNERIA, ELETTROMAGNETISMO E
NANOSCIENZE

Titolo della tesi: Microgels at interfaces: from single-particle modeling to collective behavior

Colloids are micro- or nano-sized particles that are increasingly used as model system to address fundamental issues in soft matter science. Microgels in particular are characterized by a crosslinked polymer network which provide them an internal elasticity and deformability. Their colloid-polymer duality clearly emerges when such particles are adsorbed at fluid-fluid interfaces, where microgels retain a so-called fried-egg shape. Despite the great theoretical and applicative interest for this system, there are several aspects that still need to be explored and, among all, the connection between the properties and conformation of a single particle and their collective behavior. In this Thesis, we aim to shed light on this aspect complementing molecular dynamics simulations and experiments. We will move from the single-particle microgel modeling in explicit solvent in the bulk, building on a coarse-grained model for microgels which provide a realistic description of the internal polymeric architecture and swelling behavior. Once this is established, we transfer this knowledge to correctly mimic the effect of the surface tension, in order to reproduce the correct extended conformation of the particle at the interface. Furthermore, by computing their effective interaction potential, we demonstrate that microgels adsorbed at an interface behave like 2D elastic particles, following the two-dimensional Hertzian theory. The analysis of the dynamical properties evidences the presence of multiple reentrant dynamics phenomena where, by continuously increasing the particle density, microgels first arrest and then refluidify due to the high penetrability of their extended coronas. In particular, we prove that this behavior can be found for small and loosely crosslinked microgels in a range of experimentally accessible conditions. A final section is dedicated to the analysis of hollow microgels that, given their topology, adopt a single particle conformation at the interface which is radically different from that of standard microgels.