Charges play a vital role for the stability of colloidal suspensions, their local and mesoscopic structure and dynamics and allow us to control and drive colloidal self-assembly. While charge effects are well characterised and understood for spherical hard colloids, the situation is less clear for more complex systems such as soft responsive particles like ionic microgels or strongly anisotropic particles with heterogeneous charge distribution like monoclonal antibodies.
Typical thermoresponsive ionic microgels possess a complex radial mass and charge density profile and often also carry long dangling chains. I will demonstrate how this complex particle architecture strongly influences the swelling behaviour of individual particles and the potential of mean force and thus the structural and dynamic properties of dilute and concentrated systems. I will also show how the interplay between the responsive nature of the particles and the large number of charges and counterions present allows us to induce and control self-assembly, e.g. the formation of colloidal molecules or binary crystals and the investigation of phase transitions, through variations of temperature and ionic strength and the application of external fields.
For anisotropic biological particles such as monoclonal antibodies [mAbs] charge effects are even more complex. Here the anisotropic Y-shaped structure combined with a complex and heterogeneous charge distribution requires much more refined models in order to describe the potential of mean force and the resulting structural and dynamic properties. These charges not only strongly influence solution properties, the colloidal stability and the phase behavior of the mAbs and thus their ability to be formulated into high concentration solutions required for pharmaceutical applications. They also need to be taken into account during the preparation of high concentration samples through ultrafiltration using centrifugal concentrators. Here the Gibbs-Donnan effect results in a concentration-dependant pH and ionic strength that in turn changes the charge state and the electrostatic contributions to the protein-protein interactions.