Open Access

A new type of hybrid dielectric based on nanoparticles with gold cores with diameters of 2.9-8.2 nm and covalently bound thiol-terminated polystyrene shells (Mn = 5000 Da and Mn = 11000 Da) is introduced. Particle dispersions were spin coated as dielectric films of thin film capacitors. The metal contents were 5-31 vol%, and the particles packed randomly or in face-centred-cubic superstructures, mainly depending on the polymer shell. Films with 9 vol% metal and 2.9 nm cores had dielectric constants of 98@1 Hz. Small angle X-ray scattering, transmission electron microscopy, and impedance spectroscopy indicate that classical random capacitor-resistor network models partially describe the hybrid materials. The covalently attached polymer shells enabled higher metal contents than in conventional nanocomposites without the risk of conductive breakdown. Dielectric properties depended on the metal content and the core size, but not on the network structure. The frequency-dependent dielectric polarization mainly takes place at the interfacial areas, but is not considered in the classical models. Smaller core sizes increased internal interfacial areas at comparable metal fractions by 46 %, resulting in 40 % larger dielectric constants in agreement with the Maxwell-Wagner-Sillars model. Inkjet-printed capacitors were prepared with a capacitance of 2.0±0.1 nF@10 kHz over an area of 0.79 mm² on rigid substrates; they retained their functionality over 3500 bending cycles on flexible substrates.

Inorganic nano-objects with organic shells form an interesting class of nanostructured materials when they are assembled into larger units - hybrid materials. The industrial use of materials produced via this bottom-up route is impeded by the lack of simple production processes. A promising process is their production from colloidal inks; however, the targeted control of the nano-objects’ superstructure formation must be improved. Here interfaces and the organic shells are crucial, as they strongly affect the assembly characteristics of the hybrid nano-objects. Here, the colloidal and supramolecular chemistry of the ligand shell is studied. Ligandstabilized wire-like and rod-like nano-objects were synthesized, modified, and their assembly behavior in conjunction with the dispersant medium was elucidated. After that, two different hybrid materials were produced using an ink-based approach. First, gold nanorods were coated with a conjugated polymer ligand shell that enabled both good colloidal stability and electrical conductivity of the hybrid structures directly after drying of the ink without sintering. Second, ultrathin gold nanowires were spun into hierarchical fibers, exploiting the interaction of their ligand shells with the surrounding dispersant medium.

Transparent electrodes (TEs) are key components of modern optoelectronic devices like touch screens, solar cells, and OLEDs, but an inherent trade-off between high electrical conductivity and optical transparency limits the available material range. Indium tin oxide (ITO) has been dominating the market, but cannot provide the mechanical flexibility that novel devices based on polymer substrates require; high process temperatures required for high-grade ITO exceed the thermal budget of many polymers. Solutionprocessed metal grids from nanoscale building blocks are a promising alternative providing superior mechanical flexibility at cost-effective and scalable fabrication with low thermal budget. For this dissertation, ultrathin gold nanowires (AuNWs) from wet-chemical synthesis were explored as novel base material for TEs. Plasma sintering was shown to ameliorate the wires’ high contact resistances and poor stability. A novel nanoimprinting process was developed to pattern AuNWs into grids. The method relies on the large flexibility of the AuNWs and their ability to self-assemble into continuous hierarchical superstructures in the cavities of a pre-patterned elastomeric stamp. The process yielded ordered grids with submicron linewidth at low thermal budget, thus going beyond state-of-theart printed grids. The grids also showed competitive optoelectronic properties and superior mechanical flexibility to the incumbent materials and were applied as TEs in touch sensors.

In this thesis, block copolymers are used to rationally structure inorganic and hybrid materials into ordered, percolating nanostructures. The tunability of the microstructure, chemical composition, and porosity is explored and correlated with the materials’ performance in energy storage and conversion applications. Dense and thick mesoporous TiO2/C hybrid monoliths were prepared by co-assembly with a triblock copolymer and characterized as potential lithium ion battery anodes. The structure-directing polymer was carbonized to retain a thin conductive carbon layer at the electrolyte|electrode interface that increases the intrinsic conductivity of the active material. Polymer electrolytes were prepared by tailoring the individual blocks of the block copolymer. A minor conductive block decoupled ionic mobility from slow polymer relaxation, while sufficient mechanical stability was provided by covalently linked, mechanically stronger, insulating blocks. This combination overcomes a common trade-off between high conductivity and strength. Photocatalysis requires direct access of reactants and incident photons to a catalysts’ surface. The final part of the thesis shows that complete thermal removal of the template can create a mesoporous inorganic percolating network. Structuring the catalyst in this way improved the efficiency of photocatalysis as it combines high pore diffusibility with improved charge carrier transport properties.