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@PHDTHESIS{Jung:1022972,
author = {Jung, Oliver},
othercontributors = {Möller, Martin and Pich, Andrij},
title = {{D}arstellung lichtschaltbarer, bistabiler
{M}ikrogelstrukturen},
school = {RWTH Aachen University},
type = {Dissertation},
address = {Aachen},
publisher = {RWTH Aachen University},
reportid = {RWTH-2025-10404},
pages = {1 Online-Ressource : Illustrationen},
year = {2025},
note = {Veröffentlicht auf dem Publikationsserver der RWTH Aachen
University 2026; Dissertation, RWTH Aachen University, 2025},
abstract = {This dissertation investigates light driven microswimmers
based on thermoresponsive microgel, aiming to establish the
foundation for autonomous micro swimmers through
self-oscillation. After developing and discussing the design
principles, it first highlights the ability of a bilayer
gold/hydrogel ribbon to perform work under critical
conditions. It then demonstrates how directional motility
can be achieved by purposeful shaping of bilayer ribbons.
Furthermore, it is demonstrated how radially confined gel
disks buckle into domes when swollen, and how different
modes of actuation enable swimming and directed motility.
Ultimately, by combining the previously developed components
- a bilayer under radial confinement - and adding
pre-strain, a light-switchable, bistable microgel is
created. The first section discusses the essential design
elements of an autonomous micro swimmer and provides
examples how these can be realized based on thermoresponsive
Poly(N-isopropylacrylamide) (PNIPAm) microgel with embedded
gold nanorods. Near infrared (NIR) light is transformed into
mechanical energy, enabling non-equilibrium actuation. By
alignment of the gold nanorods, optical feedback loops are
created that self-control the energy uptake, which in
combination with bistability enables self-oscillation, and
together with features for directional motion a fully
autonomous micro swimmer. The effectiveness of the proposed
system is highlighted in the second section: A hydrogel
bilayer ribbon capable of direct temperature-to-motion
conversion by embedding gold nanorods and leveraging the
volume phase transition (VPT) of the gel at 32°C. The
differential swelling between the layers induces bending
deformation, resulting in curvature inversion across the
VPT. This transition drives a shape deformation work cycle,
and close to the VPT temperature variations of less than
one-third of a centigrade trigger amplified motion,
visualized by tracer particles moving faster than Brownian
motion. Moreover, it is shown how wedge-shaped bilayer
ribbons form conical helices when swollen and extend into
filament-like shapes above the hydrogel’s VPT. NIR-light
pulses enable rapid temperature cycling and trigger
different modes of actuation on both ends of the ribbon.
This causes the ribbons to achieve directional locomotion of
up to 6 body lengths per seconds, with the wider end
leading. By modulating the actuation frequency the motion
can be shifted between spinning and translating forward. The
dissertation further presents a gold nanorods laden hydrogel
disks that swell into a domes with an evenly distributed,
azimuthal wrinkling pattern when radially confined by an
inextensible annulus. The dome height scales linearly with
its base radius, while the wrinkle count follows a power-law
relationship with the disk’s aspect ratio. Upon
irradiation, the dome flattens, recovering its wrinkled
state upon cooling, exhibiting a shape deformation
hysteresis. This enables the dome to translate along the
substrate, independent of the incident light angle. The
dome’s motion also manipulates surrounding microspheres,
demonstrating potential for load-carrying and dispersal. The
key innovation is a light switchable, bistable hydrogel
dome. The design, featuring a PNIPAm hydrogel disk coated
with polyacrylate and radially compressed within the
annulus, combines active and passive layers for controlled
deformation. The annulus creates an energy barrier between
two stable states, enabling a snap-through transition. Both
states of the dome with the passive layer facing inwards and
outwards, respectively, coexist and are distinguishable by a
characteristic wrinkling pattern. By maximizing the cooling
and heating rate a snap-through transition as low as two
milliseconds is observed.},
cin = {154610 / 150000},
ddc = {540},
cid = {$I:(DE-82)154610_20140620$ / $I:(DE-82)150000_20140620$},
typ = {PUB:(DE-HGF)11},
doi = {10.18154/RWTH-2025-10404},
url = {https://publications.rwth-aachen.de/record/1022972},
}
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