Electrochemical switching and synthesis of microgels

  • Elektrochemisches Schalten und Synthese von Mikrogelen

Schneider, Sabine; Plamper, Felix Alois (Thesis advisor); Richtering, Walter (Thesis advisor)

Aachen (2020)
Dissertation / PhD Thesis

Dissertation, RWTH Aachen University, 2020

Abstract

Stimuli-responsive polymer systems can adapt their properties in response to environmental changes. Here, the electrochemical stimulus is, despite its simple and precise controllability, less often investigated compared to e.g. pH or temperature stimuli. This is also true for microgels being mostly spherical, cross-linked polymer networks in the range of nanometres to micrometres. To tailor the properties of these microgels, the distribution of functional comonomers in the polymer network is highly important. As soft anisotropic colloids are exciting building blocks for self-assembly processes, also the control over the shape of the resulting microgels attracts attention.Starting from a poly(N-isopropylacrylamide-co-vinylferrocene) (P(NIPAM-co-VFc)) microgel with a VFc-rich core and a NIPAM-rich shell, the synthesis protocol is adapted within this thesis to control the distribution of the VFc monomer. By combining model-based synthesis predictions with experimental work, microgels with a homogeneous VFc distribution and a VFc-rich shell were easily synthesised. Placing the electro-active VFc units in the shell enhances their electrochemical addressability in organic media. In aqueous solution, the low dynamics in the VFc-rich spots seem to hinder or even prevent electrochemical addressability. Additionally, the formation of anisotropic microgels via spatially resolved electrodeposition is studied. To realise a polymer film that replicates a 2D electrode structure, different polymer systems and electrode properties were investigated. The deposition performance of the quaternized homopolymers poly[2-(methacryloyloxy)ethyl]trimethylammonium chloride (PMOTAC), poly[2-(acryloyloxy)ethyl]trimethylammonium chloride (POTAC) and poly[3-(methacrylamido)propyl]trimethylammonium chloride (PMAPTAC) and their copolymers with N-(3-aminopropyl)methacrylamide hydrochloride (APMA) was studied. In a further step, P(MAPTAC-co-APMA) was modified with thermally cross-linkable units to be able to ensure the structural integrity of the electrodeposited films. After investigating different materials, platinum ring electrodes embedded in a, with poly(ethylene glycol) brushes, silanized silicon dioxide matrix seem to be most suitable for the electrodeposition process. When dipping this electrode from above into the deposition solution, the electrode shape seems to dictate the shape of the electrodeposited polymer film. With increasing charge transfer the preservation of the ring cavity fails probably as the adhesion of polymer film onto the insulating silicon dioxide layer cannot be fully prevented.

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