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The surface activation of high‐density polyethylene powder using a remote plasma process at atmospheric pressure is investigated. The developed circulating fluidized bed plasma reactor enables to carry fine‐grained powder particles repetitively through the afterglow of 64 dielectric barrier discharges of argon with O2 and CO2 admixtures. The evolution of particle size distribution during conveying in the reactor is monitored by laser diffraction and reveals that only a small particle fraction is lost during the process. The contact angle of activated powder samples steadily decreases with increasing treatment time. The surface activation is most effective for O2 admixtures of 0.25 vol% and CO2 admixtures of above approximately 1 vol%, respectively.

Although microplastics are ubiquitous in today’s natural environments, our understanding of the materials, quantities, and particle sizes involved remains limited. The recovery of microplastics from different types of environmental matrices requires standardized matrix digestion protocols that allow inter-laboratory comparisons and that have no effect on the polymers themselves. A number of commonly used digestion methods rely on oxidation with concentrated hydrogen peroxide solutions to remove organic matter from the matrix. However, this can alter the nature of polymers through hydrolysis and often does not lead to a complete matrix removal. We have therefore investigated the use of two altered matrix digestion protocols, an acidic (Fenton) protocol and a new alkaline (Basic Piranha) protocol, focusing mainly on the effect on biodegradable polymers (polylactide, polybutylene adipate terephthalate, polybutylene succinate) and polymers with known degradation pathways via hydrolysis (thermoplastic polyurethanes, polyamide). Comparing the initial surface textures, chemical compositions, and particle size distributions with those obtained after digestion revealed that the Fenton protocol left most of the polymers unchanged. The ferrous residue that remains following Fenton digestion had no effect on either the polymer composition or the particle size distribution, but could disturb further analytics (e.g. Raman microscopy due to auto-fluorescence). While increasing the chance of complete matrix removal, the more powerful Basic Piranha protocol is also more likely to affect the polymer properties: Polylactide polymers in particular showed signs of degradation under alkaline digestion (reduced polylactide content, holes in the polymer matrix), indicating the unsuitability of the Basic Piranha protocol in this specific case. Polyamide, however, remained stable during the Basic Piranha treatment, and the surface chemistry, the particle size as well as the molar mass distribution of the investigated thermoplastic polyurethanes were also not affected. Hence, this protocol offers a powerful alternative for microplastic analysis with focus on particle size in more complex environmental matrices (e.g. removal of cellulose in soil), while avoiding ferrous Fenton residue. Unexpectedly, also tire rubber, a frequent target analyte in microplastic monitoring, was found to be susceptible to artefact structures by both oxidation protocols. In summary, controls for the specific combination of polymer and sample preparation protocol are highly recommended to select the most fitting protocol. Here selected suitable combinations are reported.

The mechanical response of ultrathin NaCl crystallites of nanometer dimensions upon manipulation with the tip of a scanning tunneling microscope (STM) is investigated, expanding STM manipulation to various nanostructuring modes of inorganic materials as cutting, moving, and cracking. In the light of theoretical calculations, our results reveal that atomic-scale NaCl islands can behave elastically and follow a classical Hooke's law. When the elastic limit of the nanocrystallites is reached, the STM tip induces atomic dislocations and consequently the regime of plastic deformation is entered. Our methodology is paving the way to understand the mechanical behavior and properties of other nanoscale materials.

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The moisture transport in fabrics determines its cooling effect and therefore the wearing comfort during sudorific activities. When liquid sweat is present, the moisture absorption by a fabric is characterized by the in-plane and transplanar wicking. We investigated the effect of fabric structure and fiber count on wicking by X-ray projection images using four different polyester knit structures (rib, eyelet, interlock and modified interlock, all hydrophilic), as well as five rib knits with different fiber counts per yarn (24–192, all quasi-hydrophobic with water contact angles 89 ± 1). Experiments were conducted with two-layer samples of the same fabric exposed to different external pressures. The liquid was transported in recognizable waterfronts, which can be interpreted as distinct intra-yarn and inter-yarn in-plane wicking fronts. For layer-to-layer wicking in hydrophilic samples, pressure-dependent time delays were observed; the delays correlated negatively with the relative void area at the interface, and were shortest for the rib knits. For the quasi-hydrophobic samples, however, the liquid wicked up to the upper layer without time delays, which was due to the liquid being pressed into the fabric, that is, due to the supply-driven flow. We distinguish this from the supply-limited flow, which is driven by capillary forces. The presented results have implications for the design of clothing systems for sudorific activities.

Silica-like nanoparticles are produced from four different organosilicon monomers HMDSO, TMDSO, TEOS and TMOS in a continuous non-equilibrium plasma reactor. The nanoparticle synthesis is studied as a function of the process pressure, plasma power, gas velocity,and gas composition (Ar:O 2 :monomer). The morphology, mass production,and chemical composition of the plasma formed particlesare investigated. An adapted particle growth model for a continuous plasma reactor is introduced which explains the influence of the different process parameters on particle evolution. The morphology of the produced amorphous particles is similar to fumed silica, with primary particles in the size range of 10 nm building hard-agglomerates of several hundred nanometers during the synthesis.