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@PHDTHESIS{MichalskaWalkowiak:943013,
author = {Michalska-Walkowiak, Joanna},
othercontributors = {Förster, Stephan Friedrich and Mayer, Joachim},
title = {{S}welling and association kinetics of linear
{PNIPAM}-based polymers at the phase transition},
school = {RWTH Aachen University},
type = {Dissertation},
address = {Aachen},
publisher = {RWTH Aachen University},
reportid = {RWTH-2023-01356},
pages = {1 Online-Ressource : Illustrationen, Diagramme},
year = {2022},
note = {Veröffentlicht auf dem Publikationsserver der RWTH Aachen
University 2023; Dissertation, RWTH Aachen University, 2022},
abstract = {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.},
cin = {155710 / 150000 / 049850},
ddc = {540},
cid = {$I:(DE-82)155710_20190327$ / $I:(DE-82)150000_20140620$ /
$I:(DE-82)049850_20191118$},
pnm = {DFG project 191948804 - SFB 985: Funktionelle Mikrogele und
Mikrogelsysteme (191948804)},
pid = {G:(GEPRIS)191948804},
typ = {PUB:(DE-HGF)11},
doi = {10.18154/RWTH-2023-01356},
url = {https://publications.rwth-aachen.de/record/943013},
}
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