Particles at Interfaces

Colloidal particles strongly adsorb to liquid interfaces, which provides an ideal two-dimensional confinement for the investigation of self-assembly processes. We correlate the interfacial properties and morphology of colloidal particles and soft microgels with their self-assembly and phase behaviour. We use this fundamental understanding of interfacial self-assembly to control the order and symmetry in colloidal monolayers.

Soft Particles at Interfaces

Hard and soft particles strongly adsorb to liquid interfaces, leading to the formation of a two-dimensional crystal at the interface. The resulting particle arrangement is determined by the balance between attractive and repulsive forces of the interacting colloidal particles. While for hard spherical particles the capillary attraction generally leads to hexagonally close-packed monolayer at the air/water interface, soft microgel particles exhibit a more complex interfacial behaviour. They deform into a core-corona structure under the influence of surface tension at an interface. The interaction between these flattened coronae dominates the interfacial properties and the resulting phase behaviour. In the Vogel lab, we investigate this unique phase behaviour of microgels.

Phase Transitions of Core-Shell Particles

Core-shell particles are closely related to microgels with the difference that their cores are solid and consist of a different material than the shell. A particular example on how to achieve core-shell morphologies is the mixing rigid spherical colloids and soft interfacial components. This provides a wide playground to study interfacial phase behaviour, as the soft components can manipulate the interaction potential of the rigid colloidal particles. This modification results in unexpected self-assembly structures, including chain and square packing as minimum energy configurations.

A Dirty Story

Even though the fabrication of hexagonal colloidal monolayers is well established, it is far from trivial and the monolayer quality can fluctuate between individual samples and experiments. We recently identified that amphiphilic oligomeric species are present in polystyrene colloidal dispersions and can negatively affect the self-assembly behavior. We developed cleaning protocols and robust methods to circumvent the effect of impurities and reliably form well-ordered colloidal monolayers at liquid interfaces.