Catalytic Microgel Reactions at Interface of Immiscible Droplets

• Applicants: Professor Dr. Andrij Pich; Professor Dr.-Ing. Uwe Schnakenberg
• Subject Area: Polymer Materials ; Microsystems
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 492353574

In the current DFG project “Catalytic Microgel Reactions at Interfaces of Immiscible Droplets” the technological prerequisites have been developed to study the catalytic performance of surface-active microgels at the interface of two immiscible droplets using a digital microfluidic (DMF) platform. Merged immiscible droplets form a well-defined interface that allows interfacial reactions to be studied quantitatively at the droplet level. With the implementation of new driver components, the DMF platform is now capable of ad-dressing 160 electrodes at up to 250 VRMS and 50 kHz. An electrode array design was developed and characterized for the separation of merged immiscible 1-octanol/water droplets with minimal residue, using a tear-off edge of a hydrophilic well. We have successfully synthesized a novel colloidal catalyst by incorporating a catalytically active isoselenazolebased comonomer into poly(N-isopropylacrylamide) (PNIPAm) based microgels and demonstrated the cata-lytic activity in solution, after adjusting our initial synthesis approach. The thiol oxidation was identified as a suitable model reaction. The proof-of-concept demonstrated the catalytic activity of the developed colloidal catalyst at the 1-octanol/water droplet interface. However, aqueous microgel solutions could not be manipulated in the DMF platform. Therefore, the overall project concept and measurement protocols will need to be modified achieve the goals of systematically studying the catalytic activity of microgel catalysts at the liquid-liquid interfaces in terms of reaction yield, selectivity, and reaction kinetics. In the one-year follow-up project, an improved electrode array will be developed capable of merging a large 1-octanol droplet with a large microgel-containing water droplet and extracting small 1-octanol droplets with reaction products for GC-MS analysis. A transparent indium tin oxide electrode array will be developed and used to scan the interface with a fiber-based UV-Vis spectrometer to study diffusion processes of spectroscopically active thiols, disulfides and polymers across the interface. The interfacial properties of the catalytically active microgels will be characterized, and their catalytic performance in emulsions will be analyzed. In addition, we will localize the catalytic functionalities in the microgel core or in the shell to assess how structural changes affect the interfacial catalytic activity. This project aims to provide new and important insights into the kinetics of reactions of colloidal catalysts at the interface of immiscible droplets. It will enable high throughput screenings and reaction processes for industrial applications.

• DFG Programme: Research Grants