Thermosensitive microgels are soft colloids that have gained popularity in recent years. They display a rich phase behaviour due to their unique soft potential and internal structure. Especially, their thermosensitivity allows us to use temperature as an external control to tune particle size, volume fraction and effective interaction potential in situ. It is relatively easy to incorporate acrylic acid during synthesis, giving rise to ionic microgels which are dressed with additional sensitivity to (amongst others) pH and salinity.
However, a quantitative understanding of the effective interactions between microgels is still lacking. Previous efforts have shown progress, but an all encompassing interaction potential predicting the full phase behaviour for these colloids has not been found yet. In the case of ionic microgels, an interaction potential – balancing the polymeric and charged nature of the colloid – has been proposed but never thoroughly tested.

In this seminar, I will discuss our recent efforts in pinpointing the interaction potential of both neutral and ionic microgels. Our main approach is through quantitative comparison of simulated pair correlation functions (g(r)s) and experimentally obtained g(r)s. In the case of neutral microgels, we find that a (multi)-Hertzian potential works well to describe both structure and dynamics of the probed state points, and that a core repulsion emerges once microgels are forced together. For the ionic microgels, their undefined swelling response to salinity and pH is investigated first via static and dynamic light scattering. Based on the surprising microgel architectures found under various charging conditions, we consider a new model to describe their interactions.