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

本课题旨在研究具有热敏末端嵌段和pH响应中间嵌段的三嵌段共聚物的自组织和动力学。端块是统计共聚物从疏水和热响应的单体和特征较低的临界溶液行为。中间嵌段是弱阳离子聚电解质，具有强烈的pH依赖性链构象。末端块的热响应特性使网络动力学控制成为可能：在低于相变的温度下，交联是动态的，而它们在上面是冻结的。应利用末端和中间块的响应性来制备完美有序的纳米结构薄膜。它们在水中或水蒸气中膨胀强烈，因此是传感器的模型系统。溶胀的程度取决于制备条件。首先，研究聚合物浓度、H值、离子强度和温度对网络结构的影响。网络动力学将研究动态光散射，在传统的方式和旋转的样本。其次，在这些结果的基础上，研究厚膜在不同相关pH值、离子强度和温度下在水中膨胀时的膨胀行为和结构变化。这些研究是利用同步加速器小角度x射线散射进行的。第三，在选定的pH值和离子强度下制备薄膜。它们在水汽膨胀和干燥过程中的膨胀行为和结构变化。此时，网络动力学将随着温度的变化而变化，以达到无缺陷结构和保存结构的目的。这些薄膜可视为传感器的模型系统。

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.