Kinetics of aggregation in thermoresponsive polymer solutions upon a pressure jump

压力跃变时热响应聚合物溶液中的聚集动力学

• 批准号: 403786900
• 负责人: Professorin Dr. Christine M. Papadakis
• 金额: --
• 依托单位: Department of Physics
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2018
• 资助国家: 德国
• 起止时间: 2017-12-31 至 2022-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/403786900?language=en
• 关键词: Kinetics; aggregation; thermoresponsive; polymer; solutions

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.

计划的研究项目解决了热响应性聚合物在水溶液中的水化与其从单相到两相状态的压力跳跃时聚集的动力学之间的关系。随着温度和压力的变化，非离子热响应性聚合物呈现椭圆形的共存线。众所周知，在高压下，聚合物在相变过程中的疏水水化程度比常压下要小得多。此外，极性基团的氢键对相变起着重要的作用。跨越相变的压力跳跃是温度跳跃的另一种选择，它提供了表征聚集动力学并将其与水合状态联系起来的可能性。与温度跃升不同的是，早期阶段也是可以访问的。此外，可以在反向压力跳跃中研究集合体的溶解情况。在这方面，使用了光透过率的时间分辨测量以及时间分辨的小角中子和X射线散射。此外，应使用依赖于温度和压力的拉曼光谱来研究聚合物和水之间的相互作用。重点讨论了三个体系：(A)PNIPAM、(B)PNIPMAM和(C)PS-b-PNIPAM两嵌段共聚物，均在水溶液中。系统A是一个参照系，我们已经在许多静态调查中对其进行了调查。与PNIPAM相比，体系B在常压下的温度诱导相变过程中具有两步行为，这是由于疏水相互作用增强所致。体系C与热敏壳层形成胶束，体系A的结果可应用于这种自组装体系。通过对集料生长的表征，确定了集料的生长机制、势垒和碰撞时间，并与水化作用有关。这样，就可以得到介观尺度上的分子相互作用和动力学之间的关系，并将其应用于更复杂的体系。