Showing papers by "Stefan Seeger published in 2019"

Hierarchical Structured Multifunctional Self-Cleaning Material with Durable Superhydrophobicity and Photocatalytic Functionalities.

Abstract: Self-cleaning materials, which are inspired and derived from natural phenomena, have gained significant scientific and commercial interest in the past decades as they are energy- and labor-saving and environmentally friendly. Several technologies are developed to obtain self-cleaning materials. The combination of superhydrophobic and photocatalytic properties enables the efficient removal of solid particles and organic contaminations, which could reduce or damage the superhydrophobicity. However, the fragility of the nanoscale roughness of the superhydrophobic surface limits its practical application. Here, a hierarchical structure approach combining micro- and nanoscale architectures is created to protect the nanoscale surface roughness from mechanical damage. Glass beads of 75 mu m are partially embedded into a low-density polyethylene film. This composite surface is coated with silicone nanofilaments (SNFs) via the droplet-assisted growth and shaping approach, providing the nanoscale surface roughness as well as the support for the photocatalyst with enlarged surface area. TiO2 nanoparticles, which serve as the photocatalyst, are synthesized in situ on SNFs through a hydrothermal reaction. The self-cleaning effect is proved using wettability measurements for various liquids, degradation of organic contamination under UV light, and antibacterial tests. The enhanced mechanical durability of the hierarchical structure of the composite material is verified with an abrasion test.

Solvent-Free Fabrication of Flexible and Robust Superhydrophobic Composite Films with Hierarchical Micro/Nanostructures and Durable Self-Cleaning Functionality.

Abstract: Superhydrophobic surfaces hold tremendous potential in a wide range of applications owing to their multifaced functionalities. However, the mechanochemical susceptibility of such materials hinders their widespread usage in practical applications. Here, we present a simple, solvent-free, and environmentally friendly approach to fabricate flexible and robust superhydrophobic composite films with durable self-cleaning functionality. The obtained composite film features unexpected but surprising hierarchical micro/nanoscopic structures as well as robust superhydrophobicity with a water contact angle of ∼170° and a sliding angle below 4°. Notably, the composite film exhibits mechanical robustness under cyclic abrasion, tape peeling, flexing, intensive finger wiping, and knife cutting; maintains excellent superhydrophobicity after long-time exposure to a high-humidity environment; and sustains exposure to highly corrosive species, such as strong acid/base solutions and organic solvents. The robust superhydrophobicity is ascribed to the induced micro/nanohierarchical surface structures, resulting in the trapped dual-scale air pockets, which could largely reduce the solid/liquid interface. In addition, even after oil contamination, the composite film maintains its water repellency and self-cleaning functionality. The robust superhydrophobic composite film developed here is expected to extend the application scope of superhydrophobic materials and should find potential usage in various industries and daily life.

Phosphorus fluxes in a temperate forested watershed: Canopy leaching, runoff sources and in-stream transformation

Abstract: Declining foliar phosphorus (P) levels call increasing attention to the cycling of this element in temperate forests. We explored the fluxes of P in a temperate mixed deciduous forest ecosystem in six distinct hydrological compartments: Bulk precipitation and throughfall, soil water draining laterally from three different soil depths (0-15, 15-150, 150-320 cm below soil surface), groundwater, creek and spring discharge, which were sampled at daily to bi-weekly resolution from March 2015 to February 2016. Atmospheric P fluxes into the ecosystem were equally partitioned between wet and dry deposition. Approximately 10% of the foliar P stock was lost annually by foliar leaching during late summer. The concentrations of dissolved P in soil water from the forest floor and upper mineral topsoil followed a pronounced seasonal cycle with higher concentrations during the vegetation period. The concentrations of P dissolved in soil water decreased with increasing soil depth. Using an end member mixing analysis (EMMA) we found that P sources feeding the spring water were both soil water from greater depths or groundwater with season specific contributions. Atmospheric P fluxes into the ecosystem determined in this study and P-release from weathering reported for the research site were large enough to compensate P losses with runoff. This suggests that declining foliar P levels of forests are unlikely the result of a dwindling total P supply, but rather caused by tree nutrition imbalances or alternative stressors.

Chemically Resistant, Electric Conductive, and Superhydrophobic Coatings

Abstract: In this study, the fabrication of superhydrophobic and conductive coatings applying a facile coating method is reported. The droplet‐assisted growth and shaping (DAGS) method is used to synthesize silicone nanofilament–based superhydrophobic coatings. Dip coating of superhydrophobic substrates in carbon nanofiber suspensions is performed to prepare superhydrophobic/conductive coatings. The prepared coatings combine electric conductivity, optical transparency, and superhydrophobicity with low sliding angles. The coatings show stability to water immersion and exposure to extreme humid conditions. Also, they exhibit good chemical resistance after several days of immersion in acidic and basic aqueous solutions. A key factor of such coatings is the mechanical durability which is improved by the addition of Parafilm‐M

Amyloid-β Peptide-Lipid Bilayer Interaction Investigated by Supercritical Angle Fluorescence.

Abstract: The understanding of the interaction between the membrane of neurons and amyloid-β peptides is of crucial importance to shed light on the mechanism of toxicity in Alzheimer's disease. This paper describes how supercritical angle fluorescence spectroscopy was applied to monitor in real-time the interaction between a supported lipid bilayer (SLB) and the peptide. Different forms of amyloid-β (40 and 42 amino acids composition) were tested, and the interfacial fluorescence was measured to get information about the lipid integrity and mobility. The results show a concentration-dependent damaging process of the lipid bilayer. Prolonged interaction with the peptide up to 48 h lead to an extraction and clustering of lipid molecules from the surface and a potential disruption of the bilayer, correlated with the formation of peptide aggregates. The natural diffusion of the lipid was slightly hindered by the interaction with amyloid-β(1-42) and closely related to the oligomerization of the peptide. The adsorption and desorption of Amyloid-β was also characterized in terms of affinity. Amyloid-β(1-42) exhibited a slightly higher affinity than amyloid-β(1-40). The former was also more prone to aggregate and to adsorb on the bilayer as oligomer.

‘Teflon Basin’ or Not? A High-Elevation Catchment Transit Time Modeling Approach

Abstract: We determined the streamflow transit time and the subsurface water storage volume in the glacierized high-elevation catchment of the Rofenache (Oetztal Alps, Austria) with the lumped parameter transit time model TRANSEP. Therefore we enhanced the surface energy-balance model ESCIMO to simulate the ice melt, snowmelt and rain input to the catchment and associated δ18O values for 100 m elevation bands. We then optimized TRANSEP with streamflow volume and δ18O for a four-year period with input data from the modified version of ESCIMO at a daily resolution. The median of the 100 best TRANSEP runs revealed a catchment mean transit time of 9.5 years and a mobile storage of 13,846 mm. The interquartile ranges of the best 100 runs were large for both, the mean transit time (8.2–10.5 years) and the mobile storage (11,975–15,382 mm). The young water fraction estimated with the sinusoidal amplitude ratio of input and output δ18O values and delayed input of snow and ice melt was 47%. Our results indicate that streamflow is dominated by the release of water younger than 56 days. However, tracers also revealed a large water volume in the subsurface with a long transit time resulting to a strongly delayed exchange with streamflow and hence also to a certain portion of relatively old water: The median of the best 100 TRANSEP runs for streamflow fraction older than five years is 28%.

Morphology Tuneable and Multifunctional Polystyrene‐Silicone Nano‐Composite Materials

Abstract: Nanostructured materials have shown extraordinary promise for high surface area applications. Here we report the design of polystyrene (PS)-silicone nanofilaments (SNFs) composites, which can be flexibly grown on various substrates. The high surface area achieved by the SNFs is further extended by grafting with polystyrene. By changing the polymerization conditions and post treatment methods, the morphology of grafted PS is easily tuned into three types: leaf-shaped, bead-shaped and well-wrapped. The tuneable morphology of PS is optimized for oil-water separation and photocatalytic reactions and exhibited improved performances.