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@PHDTHESIS{Wnnemann:749144,
author = {Wünnemann, Patrick},
othercontributors = {Pich, Andrij and Böker, Alexander},
title = {{D}esign, fabrication and application of responsive
hydrogel micropatterns},
school = {RWTH Aachen University},
type = {Dissertation},
address = {Aachen},
reportid = {RWTH-2018-229899},
pages = {1 Online-Ressource (xii, 203 Seiten) : Illustrationen,
Diagramme},
year = {2018},
note = {Veröffentlicht auf dem Publikationsserver der RWTH Aachen
University; Dissertation, RWTH Aachen University, 2018},
abstract = {The large-scale fabrication of highly responsive
micropattern via a hydrogel imprint process is demonstrated
in the present work; firstly, in its structural variability
and secondly in its chemical and therefore responsive
flexibility in the swelling behavior. Beside the
quantitative and qualitative analysis of the transfer of the
pattern, namely the stability and swelling/deswelling in an
aqueous environment via SFM this work discusses the
application of the geometrically defined gels for the
manufacture of continuous and conducting metallic gold
nanostructures. Chapter 2 presents the idea of the process
and sets the fabrication procedure in context to the
existing literature. The generation and variation of the
wrinkled templates is realized by the interactions between
the oxidized thin hard silica-like film and the elastomeric
polydimethylsiloxane substrate in chapter 3. Both differ in
their mechanical properties and deformation (shrinkage)
during relaxation of the stretched substrate. Herein pattern
of different geometry and dimension, i.e. pocket like and
sun-like pattern, were fabricated by the assignment of
distinct flat and (sub-) microstructured
polydimethylsiloxane substrates and by the utilization of
different stretching devices. In case of sun-like pattern,
the data shows that while the number of cavity adjoining
wrinkles could be mainly increased by shorter plasma
exposure times and increasing applied strain, the
corona-width is decreased at the same time. In Chapter 4 the
print process, the formation of responsive hydrogel pattern
based on poly(N-isopropylacrylamide) and
poly(N-vinylimidazole), is discussed. The focus lies in the
visualization of the transfer to responsive gel-pattern as
well as their stability and swelling behavior in several
aqueous environments, with differing ionic strength, pH
value and temperature. The comparison between the microgel
print and the imprint of a
monomer-crosslinker-initiator-mixture to form patterned
hydrogel points out(highlights), that the usage of the
aqueous mixture evolves the print and leads to a higher
physical and chemical variability. Considering the transfer,
a minimal loss in height between the stamp and its negative
was observed. The transfer from one-dimensional,
two-dimensional and radial pattern, visualized via SFM,
revealed that complex structures down to 6-10 nm were
achieved in this process. Liquid-cell SFM analysis
demonstrated the stability of one-dimensional pattern from
air into aqueous surrounding. Further measurements
demonstrate the responsiveness of one dimensional
poly(N-isopropylacrylamide) and poly(N-vinylimidazole)
pattern in dependence of their crosslinker concentration and
their surroundings. In case of poly(N-isopropylacrylamide)
the content of N,N’-methylenebisacrylamide was varied from
5 $mol\%,$ 7.5 $mol\%$ to 10 $mol\%,$ which results in a
shift to a higher volume phase transition temperature (VPTT)
and a lower swelling degree. While
poly(N-isopropylacrylamide) is inert to the change of the
pH, the poly(N-vinylimidazole) swells at low and shrinks at
high pH values. A copolymerization of both in
equalmolarities reveals the stronger influence of the
stronger Coulomb interactions between the coordinated
charges than the influence of the increased hydrophobic
interactions induced by an increase of the temperature. In
chapter 5 a two-chamber SFM measurement cell was developed,
where the redox-responsivity of P(NIPAAm-co-MAPTAC)
microgels in presence of ferri- and ferrocyanates could be
mimicked in concentrated solutions comparable to experiments
and results from 3D-DLS. Revealing the swelling behavior of
the gels on silicon and functionalized gold surfaces shows
the strong influence of the surface on the size and swelling
behavior of the gel-particles. The hydrogel guided formation
to gold nanowires was achieved for the first time due to the
successful coordination of the metal-precursor
tetrachloroauric acid into the microstructured PVIM-network
as described in chapter 6. Here, the incubation of the ions
leads to a significant decrease in responsivity of the
hydrogel-ion-complex due to the repulsive Coulomb
interactions between the induced charges. In a second step
the gold was reduced to its elementary form by means of
reducing agent or plasma. Hereby the reduction by a reducing
agent sustains the polymer-network, whereas the reduction by
cold plasma leads to polycrystalline gold pre-structures
including a minority of organic residues. The plasma exposed
and developed gold structures were analyzed by situ
conductivity experiments and revealed resistivities of
individual gold nanowires within the range of ρ = 2.2 10-6
Ω·m to 1.4 10-7 Ω·m.},
cin = {153510 / 052200 / 150000},
ddc = {540},
cid = {$I:(DE-82)153510_20140620$ / $I:(DE-82)052200_20140620$ /
$I:(DE-82)150000_20140620$},
typ = {PUB:(DE-HGF)11},
doi = {10.18154/RWTH-2018-229899},
url = {https://publications.rwth-aachen.de/record/749144},
}
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