Understanding and controlling the lateral hydrogel shell deformation of core/shell microgels at air/water interfaces for smart surface nanopatterning

• Applicant: Professor Dr. Matthias Karg
• Subject Area: Preparatory and Physical Chemistry of Polymers
• Term: from 2019 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 426700576

The objectives of this project are the investigation and clarification of the lateral extension of freely floating colloidal monolayers of core/shell microgels at air/water interfaces. Furthermore, the monolayer extension will be used as a smart nanopatterning technique for the preparation of interacting, plasmonic surface coatings.The basis for these works will be microgels with hard cores and soft, deformable hydrogel shells. In contrast to purely polymeric microgels, these particles form highly ordered, freely floating monolayers spontaneously. In a previous proof-of-concept study we could show that the monolayers expand laterally on timescales of minutes to hours. The exact origin of this extension, its kinetics and the structural parameters influencing the extension behavior are currently unknown. We could merely show that the extension occurs very slowly and that the degree of order of the monolayer during extension remains nearly unaffected. Based on this knowledge we want to study the kinetics of extension in dependence of different structural and external parameters. For this, we will synthesize core/shell microgels of different softness, cross-linker distribution and charge. These will be characterized with respect to their swelling capacity and surface activity. A central task will be the determination of the difference in surface pressure between covered and uncovered areas of the interface. We will use the transfer of the freely floating monolayers onto glass substrates after different dwell times to study the temporal evolution of the microstructure by different microscopy techniques. By varying the size of the monolayer area at the interface and the reduction of the surface tension through a surfactant, we will identify how the extension kinetics can be controlled by external parameters. Furthermore, for the first time it becomes possible for us to follow the monolayer extension spectroscopically in-situ by the use of dye-labeled cores. In contrast to this, experiments with microgels featuring plasmonic gold cores of various sizes will allow to clarify plasmon resonance coupling phenomena. Here we will also use in-situ spectroscopy for time dependent experiments on freely floating monolayers. We will investigate the microstructure in-situ by grazing-incidence small-angle X-ray scattering (GISAXS). With this we can derive potential correlations between monolayer structure and optical coupling processes, e.g. between localized surface plasmon resonances and diffraction modes of the superlattice. The experimental findings will be supported by theoretical calculations of the optical properties. The results of this project will contribute on the one hand to the fundamental understanding of soft systems at interfaces and on the other hand to the development of smart nanopatterning procedures for the preparation of optically active, colloidal coatings.

• DFG Programme: Research Grants