Probing Polymer Interpenetration into Polymer Brush Surfaces via Foerster Resonance Energy Transfer Chemistry

• Applicant: Dr. Khrystyna Rymsha, Ph.D.
• Subject Area: Preparatory and Physical Chemistry of Polymers ; Physical Chemistry of Molecules, Liquids and Interfaces, Biophysical Chemistry
• Term: since 2026
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 572718429

Polymer brush bilayers have emerged as promising candidates for reducing friction at soft interfaces due to the formation of a liquid-like interfacial layer. A key descriptor of their lubrication properties is the degree of mutual interpenetration between opposing polymer brushes. However, most efforts to optimise or understand these lubrication properties have been based on empirical or trial-and-error approaches. Despite notable progress, the molecular-scale chain dynamic processes occurring during lubrication are not yet fully understood. This is largely due to the inability to directly observe processes occurring at the interface between contacting surfaces (e.g., contacting colloidal probe on a brush), where the architecture of the system is inaccessible to most methods. Overcoming these challenges requires a new approach with greater experimental resolution. This project aims to address this challenge by investigating the depth of interpenetration between opposing polymer brushes, as well as penetration of the free polymer chains into the brush layers, using Förster resonance energy transfer (FRET) chemistry. Stimuli-responsive polymer brushes will be synthesised via a grafting-from approach using surface-initiated photoinduced electron transfer-reversible addition-fragmentation chain transfer (SI-PET-RAFT) polymerisation. The post-polymerisation with fluorophores will be carried out, with a donor incorporated in one brush and an acceptor in the opposing one or in free polymer chains. The interaction between free polymer chains and polymer brushes will be studied to evaluate their contribution to the lubrication performance when present at the lubrication interface. Utilising confocal laser scanning microscopy (CLSM), the penetration of free polymer chains within a broad range of molecular weights will be determined through careful spectral separation of the fluorescent emission. The combination of the colloidal probe of atomic force microscopy (CP AFM) and CLSM techniques will be used for understanding what the optimal free chain length is that effectively reduces friction and prevents brush wear. This methodology enables the quantification of the FRET efficiency as a function of the polymer brush interpenetration, ranging from partial overlap to complete separation under both shear and compression. To achieve this, the integrated CP AFM/CLSM setup will be used for real-time monitoring detection of proximately driven energy transfer between opposing paired-FRET labelled polymer under different solvency conditions. This will enable detailed insights into relationship between conformation and interpenetration on the lubrication forces between two brush-coated bodies. Successful implementation of the FRET-based conception will enable validation of the theoretical models and facilitate the prediction of optimal lubrication conditions, potentially leading to the rational design of advanced adaptive lubrication systems.

• DFG Programme: WBP Position