Thin films from pH and thermoresponsive triblock copolymers: from network dynamics to defect-free films

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The research project proposed investigates the self-organisation and dynamics of triblock copolymers which have thermoresponsive end blocks and a pH responsive middle block. The end blocks are statistical copolymers from hydrophobic and thermoresponsive monomers and feature lower critical solution behavior. The middle blocks are weak cationic polyelectrolytes which have strongly pH dependent chain conformations. The thermoresponsive properties of the end blocks enable the control of the network dynamics: At temperatures below the phase transition, the crosslinks are dynamic, whereas they are frozen above. The responsivity of the end and middle blocks shall be exploited to prepare perfectly ordered, nanostructured thin films. These swell strongly in water or water vapor and are therefore a model system for sensors. The degree of swelling depends on the preparation conditions. Firstly, the network structures will be studied in dependence on polymer concentration, H value, ionic strength and temperature. The network dynamics will be investigated with dynamic light scattering, both in the conventional way and with a rotating sample. Secondly, on the basis of these results, the swelling behavior of thick films and the structural changes shall be studied during swelling in water at different relevant pH values, ionic strength and temperatures. These investigations are carried out using synchrotron small-angle X-ray scattering. Thirdly, thin films will be prepared at selected pH values and ionic strengths. Their swelling behavior and structural changes during swelling in water vapor and during drying. At this, the network dynamics will be varied by change of temperature to achieve defect-free structures and to conserve them. These films may be considered as model systems for sensors.