% IMPORTANT: The following is UTF-8 encoded. This means that in the presence
% of non-ASCII characters, it will not work with BibTeX 0.99 or older.
% Instead, you should use an up-to-date BibTeX implementation like “bibtex8” or
% “biber”.
@PHDTHESIS{Kathrein:573840,
author = {Kathrein, Christine},
othercontributors = {Böker, Alexander and Pich, Andrij},
title = {{P}hase transitions and ordering of microphase separated
block copolymer nanostructures in electric fields},
school = {RWTH Aachen},
type = {Dissertation},
address = {Aachen},
reportid = {RWTH-2016-03753},
pages = {1 Online-Ressource (vi, 157 Seiten) : Illustrationen,
Diagramme},
year = {2016},
note = {Veröffentlicht auf dem Publikationsserver der RWTH Aachen
University; Dissertation, RWTH Aachen, 2016},
abstract = {Increasing miniaturization of electronic and data storage
devices necessitates methods which enable large area
structuring on a nanometer length scale at reasonable
prices. Block copolymers (BCP) are promising candidates for
future application in e.g. semiconductor industry, and solar
cells due to their capability to readily self-assemble into
highly ordered thermotropic or lyotropic phases on a length
scale of 10-100 nm. One of the main challenges is gaining
control over structure and orientation of block copolymer
microphases. Methods envisaged include the application of
external stimuli such as shear forces, temperature
gradients, solvent annealing, magnetic- or electric fields,
as well as chemoepitaxy, and graphoepitaxy. Benefits of
electric field-induced orientation include that they can
easily be integrated into electronic devices, are
increasingly effective on diminishing length scales, and the
rapid, stepwise tunability of field strength.This thesis
deals with the analysis of phase transitions and ordering of
block copolymer microphases induced by electric fields. The
first four chapters deal with the bulk analysis of the
effect of electric field on microphase separated diblock
copolymer nanostructures via birefringence measurements and
synchrotron SAXS. In Chapter 3 we describe the setup
developed to use birefringence measurements as a
supplementary method to synchrotron SAXS. The novel setup
enabled the analysis of the effect of strong dc electric
fields on the order-disorder transition temperature in a
large parameter window, for various block copolymer systems.
The novelty of our findings is that we identify the
parameters that evoke mixing of block copolymers when
exposed to electric fields (the difference in dielectric
permittivity (Δε) between the block copolymer constituents
and the degree of polymerization (N)). Another phase
transition focused on is the electric-field-induced
transition between a gyroid and a cylinder nanostructure.
Through a detailed synchrotron SAXS study we could unveil
the mechanisms of the electric-field-induced
gyroid-to-cylinder transition and of the reformation of the
gyroid phase after turning off the electric field which have
not been reported to date. The detailed mechanistic study is
given in Chapter 6. We show that the exploited mechanism is
determined by temperature and electric field strength. In
Chapter 5 time- and temperature-resolved in-situ
birefringence measurements were applied to analyze the
effect of nanoparticles on the electric field-induced
alignment of block copolymers. With our experiments we
reveal that the incorporation of isoprene-confined CdSe
quantum dots leads to an altered reorientation behavior.
Particle loading lowers the order-disorder transition
temperature, and increases the defect density, favoring
nucleation and growth as an alignment mechanism over
rotation of grains. Experiments to the last two chapters of
this thesis were performed during a research internship at
the Massachusetts Institute of Technology (MIT) and deal
with the effect of electric fields on thin film samples. In
Chapter 7 we systematically analyze how the combination of
two directing effects (graphoepitaxy and electric field)
influences the self-assembly of cylinder forming
polystyrene-block-poly(dimethylsiloxane) block copolymer in
thin films during solvent vapor annealing. We analyzed how
the angle between the electric field direction and the
topographic guides, as well as the dimensions of the
trenches affected both the quality of the ordering and the
direction of the orientation of cylindrical domains:
parallel or perpendicular to the topographic features. This
combined approach allows the fabrication of highly ordered
block copolymer structures using macroscopically
pre-patterned photolithographic substrates.Further
structural diversity can be achieved by adding a third block
to the polymer. Hence, Chapter 8 focuses on
electric-field-induced phase transitions in thin films of
star-shaped 3-miktoarm triblock terpolymers composed of
polyisoprene, polystyrene and
polyferrocenylethylmethylsilane. We show that the
metalorganic PFEMS block alters the behavior of the polymer
upon exposure to electric fields compared to the other block
copolymers analyzed in this thesis. Additionally, to the
previously described effect of ordering the volume fraction
of PFEMS is enhanced with increasing electric field strength
due to oxidation of the ferrocenyl groups. Therefore,
different electric field strength dependent morphological
transitions are observed. The results demonstrate the
multiple tunability of the ordered microdomain structure by
simple stimuli application.Summarizing different aspects of
electric-field-induced ordering and phase transitions in
various block copolymer systems were analyzed in this thesis
enhancing the understanding of the effect of electric fields
on the block copolymer phase diagram and pointing out
possible future applications.},
cin = {153510 / 150000},
ddc = {540},
cid = {$I:(DE-82)153510_20140620$ / $I:(DE-82)150000_20140620$},
typ = {PUB:(DE-HGF)11},
urn = {urn:nbn:de:hbz:82-rwth-2016-037536},
url = {https://publications.rwth-aachen.de/record/573840},
}
Gast ::