Mobility of Single Molecules at the Interfaces of Thin Polymer Films

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Combining nanotechnology and polymers is an extremely exciting, interdisciplinary field of research in the natural sciences and engineering. Here, interfaces are created at which processes and structures differ significantly from what was previously known from bulk. Through deeper possibilities of direct single-molecule observation in this project, we expect new insights into the dynamics at such interfaces, from which innovations that contribute to solutions to the challenges of our modern world can arise. In particular, a detailed understanding of mobility is essential for nanotechnological applications of polymeric materials, as interfaces increasingly dominate the properties of materials with increasing miniaturization. The dynamics at interfaces is of utmost relevance for electronic components, organic light-emitting diodes, solar cells or selective separation systems and membranes, among others, and also determines their long-term stability. Despite extensive research, the changes in polymer dynamics and polymer properties at interfaces are still not fully understood. One of the reasons for this is the different averaging of individual methods over the behavior of different areas of the polymer. To circumvent this, the observation of polymer dynamics at the single molecule level is necessarily required. In this project, we focus on the mobility of molecules in polymer films near an interface (air or substrate). Using modern single-molecule fluorescence methods, we observe the translational and rotational motion of single probe molecules at polymer interfaces. In contrast to earlier studies, we can now experimentally achieve the required spatial nanometer resolution, especially perpendicular to the interface. This axial resolution can be achieved by recently developed metal-induced energy transfer (MIET) imaging, which we will combine with single-molecule localization microscopy and defocused wide-field microscopy in the project using a novel, single-molecule sensitive wide-field fluorescence lifetime detector. Thus, translational and rotational motion of single molecules can be correlated with their position with unprecedented isotropic 3D resolution. Thus, we will investigate the temperature dependence of the translational and rotational motion of fluorescent probes at the interfaces of polymer films and elucidate whether and with which z-profile the mobility changes at different polymer interfaces.Our project thus represents an essential step in the transition from ensemble measurements, which average over the entire dynamics in a film, to the observation of local dynamics and will decisively expand the understanding of the mobility of (macro)molecules in the vicinity of interfaces in the nanometer range.