Sub-Micron Replication of Fused Silica Glass and Amorphous Metals for Tool-Based Manufacturing.

The growing importance of submicrometer-structured surfaces across a variety of different fields has driven progress in light manipulation, color diversity, water-repellency, and functional enhancements. To enable mass production, processes like hot-embossing (HE), roll-to-roll replication (R2R), and injection molding (IM) are essential due to their precision and material flexibility. However, these processes are tool-based manufacturing (TBM) techniques requiring metal molds, which are time-consuming and expensive to manufacture, as they mostly rely on galvanoforming using templates made via precision microlithography or two-photon-polymerization (2PP). In this work, a novel approach is demonstrated to replicate amorphous metals from fused silica glass, derived from additive manufacturing and structured using hot embossing and casting, enabling the fabrication of metal insets with features in the range of 300 nm and a surface roughness of below 10 nm. By partially crystallizing the amorphous metal, during the replication process, the insets gain a high hardness of up to 800 HV. The metal molds are successfully used in polymer injection molding using different polymers including polystyrene (PS) and polyethylene (PE) as well as glass nanocomposites. This work is of significant importance to the field as it provides a production method for the increasing demand for sub-micron-structured tooling in the area of polymer replication while substantially reducing their cost of production.

Two-Photon Polymerization of Nanocomposites for Additive Manufacturing of Transparent Magnesium Aluminate Spinel Ceramics.

Transparent polycrystalline magnesium aluminate (MAS) spinel ceramics are of great interest for industry and academia due to their excellent optical and mechanical properties. However, shaping of MAS is notoriously challenging especially on the microscale requiring hazardous etching methods. Therefore, a photochemically curable nanocomposite is demonstrated that can be structured using high-resolution two-photon lithography. The printed nanocomposites are converted intro transparent MAS by subsequent debinding, sintering, and hot isostatic pressing. The resulting transparent spinel ceramics exhibit a surface roughness Sq of only 10 nm and can be shaped with minimum feature sizes of down to 13 µm. This technology will be important for the production of microstructured ceramics used for optics, photonics, or photocatalysis.

Tungsten Oxide Coated Liquid Metal Electrodes via Galvanic Replacement as Heavy Metal Ion Sensors.

Gallium liquid metals (LMs) like Galinstan and eutectic Gallium-Indium (EGaIn) have seen increasing applications in heavy metal ion (HMI) sensing, because of their ability to amalgamate with HMIs like lead, their high hydrogen potential, and their stable electrochemical window. Furthermore, coating LM droplets with nanopowders of tungsten oxide (WO) has shown enhancement in HMI sensing owing to intense electrical fields at the nanopowder-liquid-metal interface. However, most LM HMI sensors are droplet based, which show limitations in scalability and the homogeneity of the surface. A scalable approach that can be extended to LM electrodes is therefore highly desirable. In this work, we present, for the first time, WO-Galinstan HMI sensors fabricated via photolithography of a negative cavity, Galinstan brushing inside the cavity, lift-off, and galvanic replacement (GR) in a tungsten salt solution. Successful GR of Galinstan was verified using optical microscopy, SEM, EDX, XPS, and surface roughness measurements of the Galinstan electrodes. The fabricated WO-Galinstan electrodes demonstrated enhanced sensitivity in comparison with electrodes structured from pure Galinstan and detected lead at concentrations down to 0.1 mmol·L-1. This work paves the way for a new class of HMI sensors using GR of WO-Galinstan electrodes, with applications in microfluidics and MEMS for a toxic-free environment.

Injection Molding of Magnesium Aluminate Spinel Nanocomposites for High-Throughput Manufacturing of Transparent Ceramics.

Transparent ceramics like magnesium aluminate spinel (MAS) are considered the next step in material evolution showing unmatched mechanical, chemical and physical resistance combined with high optical transparency. Unfortunately, transparent ceramics are notoriously difficult to shape, especially on the microscale. Therefore, a thermoplastic MAS nanocomposite is developed that can be shaped by polymer injection molding at high speed and precision. The nanocomposite is converted to dense MAS by debinding, pre-sintering, and hot isostatic pressing yielding transparent ceramics with high optical transmission up to 84 % and high mechanical strength. A transparent macroscopic MAS components with wall thicknesses up to 4 mm as well as microstructured components with single micrometer resolution are shown. This work makes transparent MAS ceramics accessible to modern high-throughput polymer processing techniques for fast and cost-efficient manufacturing of macroscopic and microstructured components enabling a plethora of potential applications from optics and photonics, medicine to scratch and break-resistant transparent windows for consumer electronics.

Stimulus-Responsive Polyelectrolyte Surfaces: Switching Surface Properties from Polycationic/Antimicrobial to Polyzwitterionic/Protein-Repellent.

Surfaces coated with polyzwitterions are most well-known for their ability to resist protein adsorption. In this article, a surface-attached hydrophobically modified poly(carboxybetaine) is presented. When protonated by changes of the pH of the surrounding medium, this protein-repellent polyzwitterion switches to a polycationic state in which it is antimicrobially active and protein-adhesive. The pH range in which these two states exist are recorded by zeta potential measurements. Adsorption studies at different pH values (monitored by surface plasmon resonance spectroscopy) confirm that the adhesion of protein is pH dependent and reversible, that is, protein can be released upon a pH change from pH 3 to pH 7.4. At physiological pH, the poly(carboxyzwitterion) is antimicrobially active, presumably because it becomes protonated by bacterial metabolites during the antimicrobial activity assay. Stability studies confirm that the here presented material is storage-stable, yet hydrolyses after longer incubation in aqueous media.

First experimental evidence for the elusive tetrahedral cations [EP3]+ (E = S, Se, Te) in the condensed phase.

Condensed phase access to the unprecedented tetrahedral cations [EP3]+ (E = S, Se, Te) was achieved through the reaction of ECl3[WCA] with white phosphorus ([WCA]- = [Al(ORF)4]- and [F(Al(ORF)3)2]-; -RF = -C(CF3)3). Previously, [EP3]+ was only known from gas phase MS investigations. By contrast, the reaction of ECl3[A] with the known P3 3- synthon Na[Nb(ODipp)3(P3)] (enabling AsP3 synthesis), led to formation of P4. The cations [EP3]+ were characterized by multinuclear NMR spectroscopy in combination with high-level quantum chemical calculations. Their bonding situation is described with several approaches including Atoms in Molecules and Natural Bond Orbital analysis. The first series of well-soluble salts ECl3[WCA] was synthesized and fully characterized as starting materials for the studies on this elusive class of [EP3]+ cations. Yet, with high [ECl3]+ fluoride ion affinity values between 775 (S), 803 (Se) and 844 (Te) kJ mol-1, well exceeding typical phosphenium ions, these well-soluble ECl3[WCA] salts could be relevant in view of the renewed interest in strong (also cationic) Lewis acids.