Switchable self-assembly of hardcore/soft-shell composite microgels

Go, Dennis; Möller, Martin (Thesis advisor); Pich, Andrij (Thesis advisor)

Aachen (2018)
Dissertation / PhD Thesis

Dissertation, RWTH Aachen University, 2018

Abstract

The diversity and dexterity of nature’s pathways to create complex materials have always inspired scientific research to better understand the process of guided and directed self- assembly. Self-assembly is a powerful tool, occurring from the nanoscale up to macroscopic dimensions, to organize highly functional building blocks in a purposeful manner. While investigating the interaction potential of soft colloidal building blocks, I will here explore new material systems utilizing new concepts of self-assembly. Colloidal fluorescent-core/microgel shell particles represent ideal building blocks to investigate self-assembly because their functionalities and interaction forces are tunable and they can easily be followed by using microscopy. The fusion of hard-sphere-like particles with adaptable microgels provides colloidal building blocks with a highly tunable soft interaction potential. In many natural systems, the assembly of functional building blocks into intricate structures relies on the consumption of external energy input. As long as this energy source is provided, the assembled structures sustain. Here, I connect our colloidal system to a light-triggered fuel cycle to gain temporal and kinetic control to enable the formation of more complex hierarchical assemblies. The precise control over the interparticle forces allows me to study the dynamics of phase behavior and tune the properties of the colloidal assemblies on a macroscopic scale. Although deviating from equilibrium conditions by coupling our microgel system to a dissipative reversible reaction network increases the complexity, the thereby obtained control over the colloidal system reaches far beyond that of classical colloidal self-assembly. In this work, I present the establishment of an advanced colloidal system and study its phase behavior. I further investigate the switchability of the system, which allows for potential applications in the field of adaptable optical filters and photonic devices. The studies comprise (1) the programmable co-assembly of oppositely charged microgels, (2) programmable phase transitions in a photonic microgel system – linking soft interactions to a temporal pH gradient and (3) the dissipative disassembly of colloidal microgel crystals driven by a coupled cyclic reaction network. All discussed topics are based on the same colloidal building blocks but reveal different specific phase behavior and new potential fields of application. Beyond the scope of this thesis, I also present the investigation of polyacrylonitrile in the form of fluorescent particles and as conducting electrodes in supercapacitors, which are described in additional chapters of this work.