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%0 Thesis
%A Jung, Oliver
%T Darstellung lichtschaltbarer, bistabiler Mikrogelstrukturen
%I RWTH Aachen University
%V Dissertation
%C Aachen
%M RWTH-2025-10404
%P 1 Online-Ressource : Illustrationen
%D 2025
%Z Veröffentlicht auf dem Publikationsserver der RWTH Aachen University 2026
%Z Dissertation, RWTH Aachen University, 2025
%X 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.
%F PUB:(DE-HGF)11
%9 Dissertation / PhD Thesis
%R 10.18154/RWTH-2025-10404
%U https://publications.rwth-aachen.de/record/1022972