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%0 Thesis %A Michalska-Walkowiak, Joanna %T Swelling and association kinetics of linear PNIPAM-based polymers at the phase transition %I RWTH Aachen University %V Dissertation %C Aachen %M RWTH-2023-01356 %P 1 Online-Ressource : Illustrationen, Diagramme %D 2022 %Z Veröffentlicht auf dem Publikationsserver der RWTH Aachen University 2023 %Z Dissertation, RWTH Aachen University, 2022 %X Stimuli-responsive polymer systems are intensely investigated for applications in biotechnology and medicine. Temperature and pressure are among the most important regulative parameters for responsive polymers. The most significant responsiveness occurs at the volume phase transitions of polymers exhibiting a lower (LCST) or upper (UCST) critical solution temperature. Stimuli-responsive polymers offer the possibility to systematically vary chemical structure and functionality, shape, internal architecture, and crosslinking density to design the response and its kinetics. Despite its importance, there is still a lack of fundamental knowledge about polymer volume phase transition kinetics. In the present thesis, the phase transition was examined with linear PNIPAM polymers and PS-b-PNIPAM block copolymers to check the influence of morphology and polymer length on the phase transition mechanism. The response of the polymers was studied in detail by light, neutron, and X-ray scattering, transmission electron microscopy, and optical transmittance, where important complementary information could be obtained about the complex behavior across the LCST. An abrupt and sharp phase transition was observed for the examined polymers, with an intrinsic hysteresis window between swollen and aggregated particles. It could be demonstrated that switching between states allows writing, reading, and storing information in polymer solutions within the hysteresis temperature range. Moreover, bistability, remanence and reversible information storage were realized. Information can be written on a thin layer backscattering device by cooled or heated metal pen tips as well as by a laser pulse. The bistability in PNIPAM-based polymers can be controlled by temperature and by pH as well, providing an AND-logic gate function. The demonstrated information encoding and storage properties for simple linear PNIPAM polymers provide new insight into responsive materials' application. The kinetics of the phase transition for PNIPAM-based polymers over a broad time scale was investigated using two experimental methods, where the transition was induced by a rapid temperature jump above LCST. One of them is time-resolved small-angle neutron scattering with a stopped-flow device, which tracks the size evolution of the polymers. The temperature jump can be induced on the time scale from milliseconds to minutes, where the early stage of cluster formation is observed, with further aggregation of the clusters. A multi-step aggregation was observed with the variation of polymer concentration. The second method allows following changes of turbidity within nanoseconds, where the temperature jump was induced by NIR-laser pulses. The transition mechanism for heating and cooling processes is described, from microseconds to minutes. The solution was rapidly heated or heated and kept for a few seconds above LCST to distinguish the differences in kinetics mechanism. The responsiveness of polymers with different morphology shows a lot of similarities. However, within the same polymeric system, a change of the polymer chain end-group leads to differences in the swelling process. Every step on the kinetics mechanism can be described by a characteristic time, thus that the rate constant of every process can be determined. The used methods in this thesis enable to distinguish the contributions from collapse/swelling transitions, aggregation/swelling, and phase separation/mixing processes during the volume phase transition. Within the hysteresis temperature range, deep and shallow temperature jumps were performed for linear PNIPAM-based polymers. The conditions at which the bistable state can be kept for a long time and the minimum heating energy needed to complete the microphase separation were determined using laser pulse heating. In addition, experimental methods consisting of NIR-laser setups and a high-speed camera, allow observation of the stability of aggregates state at the heated spot and verifying a thermal diffusion distance in the polymer solution. %F PUB:(DE-HGF)11 %9 Dissertation / PhD Thesis %R 10.18154/RWTH-2023-01356 %U https://publications.rwth-aachen.de/record/943013