Complexes of Oppositely Charged Microemulsions and Polyelectrolytes (PEMECs) - Responsive Systems with Controlled Structure and High Solubilisation Capacity

• Applicant: Professor Dr. Michael Gradzielski
• Subject Area: Preparatory and Physical Chemistry of Polymers ; Physical Chemistry of Molecules, Liquids and Interfaces, Biophysical Chemistry
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 562126140

Complexes of polyelectrolyte and surfactant, due to their formation of hierachically organised assemblies, are interesting colloidal aggregates for the purpose of drug delivery. However, this approach often fails due to the rather low solubilisation capacity of such complexes for hydrophobic substances, which often cannot become enhanced sufficiently by a simple optimisation of the systems. Accordingly, a logical alternative here is to start from an already optimised surfactant formulation. These are microemulsions and in this project we want to combine ionic oil-in-water (O/W) microemulsions with oppositely charged polyelectrolytes for the formation of polyelectrolyte-microemulsion complexes (PEMECs) that form due to the strongly attractive interactions. In order, to ensure solubility even at charge neutralisation we will employ double-hydrophilic copolymers with a neutral block (PEO). In order to be able to modify the interaction strength with the microemulsion droplets, we will modify the polyelectrolyte block hydrophobically, varying the percentage of modification and chain lengths of the modification from butyl to hexadecyl. In this project we will first formulate corresponding biocompatible microemulsions and synthesise the required hydrophobically modified double-hydrophilic block copolymers (DHBC). In the next step we will prepare the PEMECs and investigate them with respect to phase behaviour and thermodynamics of complexation as a function of mixing ratio, architecture of the polyelectrolyte and size and charge of the microemulsion droplets. In parallel, the PEMEC structure will be studied by means of light scattering and neutron and x-ray small-angle scattering (SANS, SAXS), where especially SANS with its options for contrast variation shall yield very interesting results. Complementary cryo-TEM studies will allow to extend to a complete and detailed structural picture of the complexes. We will also study the PEMEC structure as a function of pH and ionic strength, as they are largely based on weak bases and acids and therefore should show responsive properties. Here we also want to study the kinetics of the changes occurring and in particular, how this is affected by the hydrophobic interactions introduced by us. Finally, we will study the loading of PEMECs with different active agents and investigate their release in aqueous medium. In summary, we will comprehensively investigate and establish PEMECs as a new class of colloidal aggregates and elucidate their potential as carriers for active agents (drug delivery). With their high monodispersity, microemulsion droplets are good model systems for studying colloidal interactions with polyelectrolytes and to learn how one can control the properties of PEMECs via the architecture of the DHBC. In addition, these systems possess high potential for possible applications as formulations in fields like pharmacy or personal care, bringing new concepts into these fields.

• DFG Programme: Research Grants