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.

计划中的研究项目解决了水溶液中热敏聚合物的水化与它们在从单相到两相状态的压力跳跃时聚集动力学之间的关系。在依赖于温度和压力，非离子热响应聚合物表现出椭圆共存线。众所周知，在高压下，聚合物在相变时的疏水水化作用比在常压下减少得少。此外，极性基团的氢键对相变起着重要的作用。跨越相变的压力跳变是温度跳变的另一种选择，并提供了表征聚集动力学并将其与水化状态联系起来的可能性。与温度跳跃相反，早期阶段也是可以接近的。此外，还可以在反向压力跳变中研究团聚体的溶解。在这种情况下，光传输的时间分辨测量以及时间分辨小角中子和x射线散射被使用。此外，利用拉曼光谱研究聚合物与水之间的相互作用随温度和压力的变化。重点研究了三种体系：(A) PNIPAM, (B) PNIPAM和(C) PS-b-PNIPAM双嵌段共聚物，均为水溶液。系统A是一个参考系统，我们已经在许多静态研究中对其进行了研究。系统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，系统B的疏水相互作用增强。系统C与热响应壳形成胶束，系统a的结果可应用于该自组装系统。从骨料生长的表征出发，确定骨料的生长机制、能量垒和碰撞次数，并与水化作用有关。通过这种方法，可以推导出分子相互作用与介观长度尺度动力学之间的关系，并将其应用于更复杂的体系。