A variety of materials with diverse structures and properties can be formed as a result of electrostatic interactions between oppositely charged macromolecules. Under defined conditions, complexation between oppositely charged polyelectrolytes can lead to a phase separation phenomenon, referred to as complex coacervation. Complex coacervation is initially seen in the form of polyelectrolyte-rich fluid droplets of 1-100 μm in size (see image), which display a unique combination of physical properties. The impact of complex coacervation is demonstrated by the numerous applications in various fields (e.g. processed foods, cosmetics) as well as it importance in many biological systems (e.g. marine organisms, tubeworms mussels).
In the Tirrell group we use polypeptides to study complex coacervation. Polypeptides have identical backbones and only differ in their side groups, making them an ideal system for this type of studies. We are interested in identifying the external parameters that affect coacervation, explore the thermodynamics of coacervate formation, and study the rheological and interfacial properties of polypeptide coacervates. To achieve this, we use a variety of experimental techniques including but not limited to turbidity, Isothermal Titration Microcalorimetry (ITC), Surface Forces Apparatus (SFA) and rheology.
Building on this work, we are also exploring how complex coacervation can be used for the development of other polyelectrolyte self-assembly structures such as coacervate core micelles or hydrogels. For the characterization of the coacervate driven self-assembled structures we use techniques such as TEM, rheology, SAXS and light scattering.
Optical micrograph of coacervate droplets formed from oppositely charged polypeptides.