Near surface dynamics of layers of non-cross-linked and cross-linked polymer architectures at solid planar surfaces

• Applicants: Dr. Olaf Holderer; Dr. Stefan Wellert
• Subject Area: Experimental and Theoretical Physics of Polymers
• Term: from 2016 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 290879244

The proposed project addresses the inner dynamics of polymer matrices of different molecular architecture in the presence of solid planar substrate. Functionalisation of solid surfaces by coating them with thin polymer films has a large impact for e.g. controlled drug release, lubrication and sensorics. In order to design new coatings knowledge about the internal structure and dynamics is essential. This offers a deeper understanding of the interaction between the polymer chains themselves, under the influence of cross-linking, with additive like in hybrid systems (drug release, sensorics) or with other surfaces (lubrication). While the structure of many of these polymer systems has been already extensively studied not much is known about their dynamics when attached to surfaces, and the proposed project will contribute to close this gap of knowledge. The project focuses on the effect of geometrical confinement on the dynamics of polymer in thin films either close to one solid interface or between two solid interfaces. Two different polymer architectures prepared on Silicon surfaces will be investigated: polymer brushes, cross-linked polymer brushes, thin hydrogel layers and adsorbed microgel particles. All types will be prepared with stimuli responsive polymers and apart from the cross-linkers the chemical composition will be the same. Dynamics profiles within different polymer architectures perpendicular to the confining surface will be determined by grazing incidence neutron spin echo spectroscopy (GINSES). Thereby, a better understanding of chain dynamics and collective dynamics of polymer architectures in a solvent close to a solid interface will be achieved. To explore the relation between dynamics, structure and mechanical properties results on the dynamics will be linked to experiments on the structure (neutron-, x-ray reflectometry, SANS, GISANS, light scattering, AFM, ellipsometry) and viscoelastic properties (AFM indentation, QCM-D). In the case of opposing surfaces and brushes a direct in-situ and contactless investigation using neutron scattering techniques will gain insight into the hydrodynamics and effects of compression and interpenetration on the chain and collective dynamics at different separation distances. The influence of rigid interfaces on the polymer dynamics and mechanics will be studied as a function of size parameters and composition (cross-linker and comonomer content).The proposed project will benefit from the strong synergy of expertise of the two groups from TU Berlin and from JCNS@MLZ. The common expertise includes synthesis, sample preparation, technical knowledge over a large variety of techniques, extension of scattering techniques (e.g. GINSES) and data analysis. The project is designed for a PhD student with an anticipated time of three years located at the TU Berlin and a Post-doc position of two years located at the JCNS outstation at the Maier-Leibnitz Zentrum in Garching.

• DFG Programme: Research Grants
• Co-Investigator: Professorin Dr. Regine von Klitzing