Scientific publications

Hybrid electronic materials combine the excellent electronic properties of metals and semiconductors with the mechanical flexibility, ease of processing, and optical transparency of polymers. This talk will discuss hybrids that combine organic and inorganic components at different scales. Metallic and semiconductor nanoparticle cores are coated with conductive polymer shells to create “hybrid inks” that can be inkjet-printed and form conductive leads without any sintering step. Transparent electrodes are printed using ultrathin metal nanowires with core diameters below 2 nm. The chemically synthesized wires spontaneously form percolating structures when patterned with a soft stamp; this rapidly yields optically transparent grid electrodes, even on demanding soft substrates. These new hybrid electronic materials enable the fabrication of soft electronics, including flexible sensors on polymer foils, radio-frequency identification (RFID) antennae on cardboard, and soft human–machine interfaces. Selected devices will be covered at the end of the talk.

The fate of polymer-coated Eu- and Bi-doped GdVO4 nanoparticles (NPs) of cubic shape upon cellular internalization was investigated. After having been endocytosed by cells, the cubic Eu- and Bi-doped GdVO4 NP cores were partly dissolved and reshaped to rounded structures, which in control experiments could be ascribed to the acidic conditions present in endosomes/lysosomes. With progress of time, there was a significant reduction in the amount of internalized NPs per cell due to proliferation. This was of higher extent than NP exocytosis. Data of the study are compatible with the scenario that endosomal/lysosomal enzymes may partly digest the polymer shell around the NP cores, with enhanced exocytosis of the polymer fragments as compared to the NP cores.

Abstract Gold nanoparticles (AuNP) are frequently used in surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS) for analysis of biomolecules because they exhibit suitable thermal and chemical properties as well as strong surface plasmonic effects. Moreover, the structures of AuNP can be controlled by well-established synthesis protocols. This was important in the present work, which studied the influence of the nanoparticles’ structures on atmospheric pressure (AP)-SALDI-MS performance. A series of AuNP with different core sizes and capping ligands were investigated, to examine the desorption/ionization efficiency (DIE) under AP-SALDI conditions. The results showed that both the AuNP core size as well as the nature of the surface ligand had a strong influence on DIE. DIE increased with the size of the AuNP and the hydrophobicity of the ligands. Chemical interactions between ligand and analytes also influenced DIE. Moreover, we discovered that removing the organic ligands from the deposited AuNP substrate layer by simple laser irradiation prior to LDI further amplified DIE values. The optimized AuNP were successfully used to analyze a wide arrange of different low molecular weight biomolecules as well as a crude pig brain extract, which readily demonstrated the ability of the technique to detect a wide range of lipid species within highly complex samples.

Semiconductor nanoplatelets exhibit spectrally pure, directional fluorescence. To make polarized light emission accessible and the charge transport effective, nanoplatelets have to be collectively oriented in the solid state. We discovered that the collective nanoplatelets orientation in monolayers can be controlled kinetically by exploiting the solvent evaporation rate in self-assembly at liquid interfaces. Our method avoids insulating additives such as surfactants, making it ideally suited for optoelectronics. The monolayer films with controlled nanoplatelets orientation (edge-up or face-down) exhibit long-range ordering of transition dipole moments and macroscopically polarized light emission. Furthermore, we unveil that the substantial in-plane electronic coupling between nanoplatelets enables charge transport through a single nanoplatelets monolayer, with an efficiency that strongly depends on the orientation of the nanoplatelets. The ability to kinetically control the assembly of nanoplatelets into ordered monolayers with tunable optical and electronic properties paves the way for new applications in optoelectronic devices.

We report on the colloidal stability of nanoparticles with alkanethiol shells in apolar solvents. Small-angle X-ray scattering and molecular dynamics simulations were used to characterize the interaction between nanoparticles in linear alkane solvents ranging from hexane to hexadecane, including 4 nm gold cores with hexadecanethiol shells and 6 nm cadmium selenide cores with octadecanethiol shells. We find that the agglomeration is enthalpically driven and that, contrary to what one would expect from classical colloid theory, the temperature at which the particles agglomerate increases with increasing solvent chain length. We demonstrate that the inverted trend correlates with the temperatures at which the ligands order in the different solvents and show that the inversion is due to a combination of enthalpic and entropic effects that enhance the stability of the ordered ligand state as the solvent length increases. We also explain why cyclohexane is a better solvent than hexadecane despite the two having very similar solvation parameters.

Ionic liquids are an attractive material class due to their wide liquid range, intrinsic ionic conductivity, and high chemical as well as electrochemical stability. However, the widespread use of ionic liquids is hindered by significantly higher viscosities compared to conventional molecular solvents. In this work, we show how the transport properties of ionic liquids can be altered significantly, even for isostructural ions that have the same backbone. To this end, structure–property relationships have been determined for a set of 16 systematically varied representative ionic liquids. Variations in molecular structure include ammonium vs. phosphonium, ether vs. alkyl side chains, and rigid vs. flexible anions. Ab initio calculations are used to relate molecular structures to the thermal, structural and transport properties of the ionic liquids. We find that the differences in properties of ether and alkyl functionalised ionic liquids are primarily dependent on minimum energy geometries, with the conformational flexibility of ether side chains appearing to be of secondary importance. We also show unprecedented correlations between anion conformational flexibility and transport properties. Critically, increasing fluidity upon consecutive introduction of ether side chains and phosphonium centres into the cation is found to be dependent on whether the anion is flexible or rigid. We demonstrate that targeted design of functional groups based on structure–property relationships can yield ionic liquids of exceptionally high fluidity.

Within this work, well-defined polystyrene-block-poly(2-hydroxyethyl methacrylate) (PS-b-PHEMA) and a non-polar model block copolymer (BCP) polystyrene-block-polybutadiene (PS-b-PB) have been prepared via sequential anionic polymerization and investigated with respect to their capability of microphase separation in the presence of cellulose fibres. Both the original morphologies in the bulk state as well as the microphase-separated structures in the vicinity of cellulose fibres were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS) measurements. BCP series featuring molar masses below 70 kg mol−1 and higher molar masses up to 201 kg mol−1 have been subjected to solvent-casting and subsequent thermal annealing to elucidate the microstructures in the presence or absence of cellulose fibres with defined contents of water. Besides the classical morphologies comprising spheres, cylinders and lamellae, also gyroidal and helical-domains were observed. Moreover, a significant impact on the degree of domain order and orientation was found for the PHEMA-containing BCPs based on the hydroxyl moiety interactions of the cellulose fibres and respective PHEMA block segments.

Abstract The direct printing of microscale quantum dot light-emitting diodes (QLEDs) is a cost-effective alternative to the placement of pre-formed LEDs. The quality of printed QLEDs currently is limited by nonuniformities in droplet formation, wetting, and drying during inkjet printing. Here, optimal ink formulation which can suppress nonuniformities at the pixel and array levels is demonstrated. A solvent mixture is used to tune the ejected droplet size, ensure wetting, and provoke Marangoni flows that prevent coffee stain rings. Arrays of green QLED devices are printed at a resolution of 500 pixels in.−1 with a maximum luminance of ≈3000 cd m−2 and a peak current efficiency of 2.8 cd A−1. The resulting array quality is sufficient to print displays at state-of-the-art resolutions.

Abstract Direct inkjet printing of functional inks is an emerging and promising technique for the fabrication of electrochemical energy storage devices. Electrochromic energy devices combine electrochromic and energy storage functions, providing a rising and burgeoning technology for next-generation intelligent power sources. However, printing such devices has, in the past, required additives or other second phase materials in order to create inks with suitable rheological properties, which can lower printed device performance. Here, tungsten oxide nanocrystal inks are formulated without any additives for the printing of high-quality tungsten oxide thin films. This allows the assembly of novel electrochromic pseudocapacitive zinc-ion devices, which exhibit a relatively high capacity (≈260 C g−1 at 1 A g−1) with good cycling stability, a high coloration efficiency, and fast switching response. These results validate the promising features of inkjet-printed electrochromic zinc-ion energy storage devices in a wide range of applications in flexible electronic devices, energy-saving buildings, and intelligent systems.