Thermoresponsive Colloidal Molecules with Tunable Directional Interactions

Small clusters assembled from spherical colloids that resemble space-filling moleculular models, so-called colloidal molecules, have emerged as highly interesting model systems in soft matter physics. Here we demonstrate that we can fabricate colloidal molecules with a well-defined number of binding sites and externally tuneable interactions. This is achieved by using microgels based on the temperature-responsive polymers poly-N-isopropylacrylamide (PNIPAM) or poly-N-isopropylmethacrylamide (PNIPMAM) as building blocks, which are then assembled into well-defined small clusters. The use of pNIPAM and pNIPMAM microgels allows for easy manipulation of the interactions between the resulting colloidal molecules via temperature, as the interaction potential between individual microgels changes from soft repulsive below the volume phase transition temperature (VPTT) of the microgels to attractive for T > VPTT. We will present different approaches to fabricate colloidal molecules, and demonstrate that microgel-based colloidal molecules represent an interesting class of colloidal building blocks with the potential to reversibly form complex structures and materials through temperature-tuneable directional interactions.