Kinetics of aggregation in thermoresponsive polymer solutions upon a pressure jump

计划的研究项目解决了在水溶液中的温敏聚合物的水合作用和它们的聚集动力学之间的关系，从单相到两相状态的压力跳变。非离子型温敏聚合物的共存曲线随温度和压力的变化呈椭圆形。众所周知，在高压下，聚合物在相变时的疏水水合作用比在大气压下减少得少。此外，极性基团的氢键对相变起着重要作用。相变过程中的压力跃变是温度跃变的一种替代方法，并提供了表征聚集动力学并将其与水合状态相关联的可能性。与温度跳跃相反，早期阶段也是可以接近的。此外，团聚体的溶解可以在反向压力跳跃中进行研究。在这方面，时间分辨测量的光传输以及时间分辨小角中子和X射线散射。此外，应使用拉曼光谱法研究聚合物和水之间的相互作用，其取决于温度和压力。三个体系是焦点：（A）PNIPAM，（B）PNIPMAM，和（C）PS-B-PNIPAM二嵌段共聚物，全部在水溶液中。系统A是一个参考系统，我们已经在许多静态研究中研究过了。体系B在大气压下的温度诱导相变具有两步行为，这是由于与PNIPAM相比增强的疏水相互作用。系统C形成具有温敏壳的胶束，并且来自系统A的结果可以应用于该自组装系统。根据骨料生长的表征，应确定骨料的生长机制、能垒和碰撞时间，并应与水化有关。这样，分子间的相互作用和动力学之间的关系，在介观尺度将被导出，这是适用于一个更复杂的系统。

The research project planned addresses the relation between the hydration of thermoresponsive polymers in aqueous solution and the kinetics of their aggregation upon a pressure jump from the one-phase to the two-phase state. In dependence on temperature and pressure, non-ionic thermoresponsive polymers exhibit an elliptical coexistence line. It is well known that, at high pressure, the hydrophobic hydration of polymers at the phase transition decreases less than at atmospheric pressure. Moreover, the hydrogen bonds of the polar groups play an important role for the phase transition. Pressure jumps across the phase transition are an alternative to temperature jumps and offer the possibility to characterize the kinetics of aggregation and to relate it to the hydration state. In contrast to temperature jumps, also the early stages are accessible. Moreover, the dissolution of aggregates can be investigated in the reverse pressure jumps. At this, time-resolved measurements of the light transmission as well as time-resolved small-angle neutron and X-ray scattering are used. In addition, the interactions between polymer and water shall be investigated using Raman spectroscopy in dependence on temperature and pressure. Three systems are in the focus: (A) PNIPAM, (B) PNIPMAM, and (C) PS-b-PNIPAM diblock copolymers, all in aqueous solution. System A is a reference system, which we have investigated in numerous static investigations. System B features two-step behavior at the temperature-induced phase transition at atmospheric pressure, which is due to the enhanced hydrophobic interactions compared to PNIPAM. System C forms micelles with a thermoresponsive shell, and the results from system A can be applied to this self-assembled system. From the characterization of the aggregate growth, the growth mechanisms, the energy barriers and the collision times of the aggregates shall be determined and shall be related to the hydration. This way, a relation between the molecular interactions and the kinetics at mesoscopic length scales will be derived, which are applied to a more complex system.