Co-nonsolvency Induced Self-Organization of Thermoresponsive Block Copolymers in Solution and in Thin Films

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The research project addresses the self-assembly of responsive amphiphilic block copolymers having different architectures (di-, tri- and star block copolymers) in mixtures of water and organic solvents under cononsolvency conditions. The block copolymers, which consistently contain poly(methylmethacrylate) as permanently hydrophobic block, use three different thermoresponsive blocks (PNIPAM, PNIPMAM and PNVIBAM), in which the molecular fine structure of the hydrophilic amide groups is systematically varied. The synthesis will be carried out using RAFT (Reversible Addition Fragmentation Chain Transfer) and switchable chain transfer agents. A special focus of the investigations is on the comparison of the cononsolvency-induced self-assembly in the bulk phase and in thin films. In the bulk, the dependence of the aggregates formed in solvent mixtures (water/methanol) on the choice of the responsive blocks, the polymer architecture and the composition of the solvent mixtures will be primarily studied, and the molecular interactions which are at the origin of the switching behavior as well as the influence of the cosolvent on the chain dynamics will be elucidated. Apart from fluorescence correlation spectroscopy, dynamic light scattering and small-angle X-ray and neutron scattering will be used. These will be complemented by spectroscopic measurements (Raman) and inelastic neutron scattering. In thin films, it will be investigated, in how far a consonsolvency behavior is also observed in contact with the vapor phase from solvent mixtures of water and organic solvents and whether/how this behavior differs in thin film and in solution. Moreover, it will be investigated in thin films which influence interactions of the block copolymers with the substrate and with the vapor phase have on the cononsolvency behavior and if film thickness plays a role. For these studies, ellipsometry, interferometry and synchrotron GISAXS measurements in microfluidic channels as well as neutron scattering experiments in liquid and vapor cells will be employed. It is also planned to investigate the dynamics of thin films from selected systems additionally with FT-IR spectroscopy and inelastic neutron scattering experiments.