164 research outputs found
What are the microscopic events of colloidal membrane fouling?
Due to the complex interplay between surface adsorption and hydrodynamic
interactions, representative microscopic mechanisms of colloidal membrane
fouling are still not well understood. Numerical simulations overcome
experimental limitations such as the temporal and spatial resolution of
microscopic events during colloidal membrane fouling: they help to gain deeper
insight into fouling processes. This study uses coupled computational fluid
dynamics - discrete element methods (CFD-DEM) simulations to examine mechanisms
of colloidal fouling in a microfluidic architecture mimicking a porous
microfiltration membrane. We pay special attention to how particles can
overcome energy barriers leading to adsorption and desorption with each other
and with the external and internal membrane surface. Interparticle interaction
leads to a transition from the secondary to the primary minimum of the DLVO
potential. Adsorbed particles can show re-entrainment or they can glide
downstream. Since particles mainly re-suspend as clusters, the inner pore
geometry significantly affects the fouling behavior. The findings allow a basic
understanding of microscopic fouling events during colloidal filtration. The
methodology enables future systematic studies on the interplay of hydrodynamic
conditions and surface energy contributions represented by potentials for soft
and patchy colloids
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Homogeneous Catalyst Recycling and Separation of a Multicomponent Mixture Using Organic Solvent Nanofiltration
In homogeneous catalysis, the application of organic solvent nanofiltration (OSN) has become a well-known alternative to common recycling methods. Even though some OSN membranes are commercially available, their classification and the scope of application have to be determined for the specific solvent mixture. The commercial membrane Evoniks DuraMemŸ 300 was tested in a mixture of ethanol, ethyl acetate, and cyclohexane with magnesium triflate as possible catalyst. The cross permeate fluxes were measured for two transmembrane pressures and the hydrodynamic radii of the components were determined. Some of the components in the ternary mixture are retained, which makes the membrane also suitable for fractioning thereof. © 2019 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinhei
A mini-module with built-in spacers for high-throughput ultrafiltration
Ultrafiltration membrane modules suffer from a permeate flow decrease arising
during filtration and caused by concentration polarization and fouling in,
e.g., fermentation broth purification. Such performance losses are frequently
mitigated by manipulating the hydrodynamic conditions at the membrane-fluid
interface using, e.g., mesh spacers acting as static mixers. This additional
element increases manufacturing complexity while improving mass transport in
general, yet accepting their known disadvantages such as less transport in dead
zones. However, the shape of such spacers is limited to the design of
commercially available spacer geometries. Here, we present a methodology to
design an industrially relevant mini-module with an optimized built-in 3D
spacer structure in a flat-sheet ultrafiltration membrane module to eliminate
the spacer as a separate part. Therefore, the built-in structures have been
conceptually implemented through an in-silico design in compliance with the
specifications for an injection molding process. Ten built-in structures were
investigated in a digital twin of the mini-module by 3D-CFD simulations to
select two options, which were then compared to the empty feed channel
regarding mass transfer. Subsequently, the simulated flux increase was
experimentally verified during bovine serum albumin (BSA) filtration. The new
built-in sinusoidal corrugation outperforms conventional mesh spacer inlays by
up to 30% higher permeation rates. The origin of these improvements is
correlated to the flow characteristics inside the mini-module as visualized
online and in-situ by low-field and high-field magnetic resonance imaging
velocimetry (flow-MRI) during pure water permeation
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Co-generation of Ammonia and H2 from H2O Vapor and N2 Using a Membrane Electrode Assembly
The direct electrochemical synthesis of NH3 from nitrogen and water vapor without the use of a fossil carbon source is highly desired. This synthesis is a viable option to store energy and produce fertilizer precursors. Here, a new Pt-free membrane electrode assembly is presented. An electrochemical membrane reactor demonstrates the feasibility of co-generating NH3 and H2 directly from nitrogen and water vapor at ambient conditions. An unprecedented high NH3-specific current efficiency of up to 27.5% using Ti as cathodic catalyst is reported. The co-generation can be tuned by the balance of process parameters. © 2019 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinhei
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Reconstruction of Ultra-thin Alveolar-capillary Basement Membrane Mimics
Alveolar-capillary basement membrane (BM) is ultra-thin (<2 ”m) extracellular matrix that maintains integral epithelial-endothelial cell layers. In vitro reconstructions of alveolar-capillary barrier supported on synthetic scaffolds closely resembling the fibrous and ultra-thin natural BM are essential in mimicking the lung pathophysiology. Although BM topology and dimensions are well known to significantly influence cellular behavior, conventionally used BM mimics fail to recreate this natural niche. To overcome this, electrospun ultra-thin 2 ”m poly(caprolactone) (PCL) nanofibrous mesh is used to establish an alveolar-capillary barrier model of lung endothelial/epithelial cells. Transepithelial electrical resistance (TEER) and permeability studies reveal integral tight junctions and improved mass transport through the highly porous PCL meshes compared to conventional dense membranes with etched pores. The chemotaxis of neutrophils is shown across the barrier in presence of inflammatory response that is naturally impeded in confined regions. Conventional requirement of 3 ”m or larger pore size can lead to barrier disruption due to epithelial/endothelial cell invasion. Despite high porosity, the interconnected BM mimic prevents barrier disruption and allows neutrophil transmigration, thereby demonstrating the physiological relevance of the thin nanofibrous meshes. It is envisioned that these bipolar cultured barriers would contribute to an organ-level in vitro model for pathological disease, environmental pollutants, and nanotoxicology. © 2021 The Authors. Advanced Biology published by Wiley-VCH Gmb
3D-printed rotating spinnerets create membranes with a twist
Round hollow fiber membranes are long-established in applications such as gas
separation, ultrafiltration and blood dialysis. Yet, it is well known that
geometrical topologies can introduce secondary ow patterns counteracting mass
transport limitations, stemming from diffusion resistances and fouling. We
present a new systematic method- ology to fabricate novel membrane
architectures. We use the freedom of design by 3D-printing spinnerets, having
multiple bore channels of any geometry. First, such spinnerets are stationary
to fabricate straight bore channels inside a monolithic membrane. Second, in an
even more complex design, a new mechanical system enables rotating the
spinneret. Such rotating multibore spinnerets enable (A) the preparation of
twisted channels inside a porous monolithic membrane as well as (B) a helical
twist of the outside geometry. The spun material systems comprise classical
polymer solutions as well as metal-polymer slurries resulting in solid porous
metallic monolithic membrane after thermal post-processing. It is known that
twisted spiral-type bore channel geometries are potentially superior over
straight channels with respect to mass and heat polarization phenomena, however
their fabrication was cumber- some in the past. Now, the described methodology
enables membrane fabrication to tailor the membrane geometry to the needs of
the membrane process
Fabrication and transfer print based integration of free-standing GaN membrane micro-lenses onto semiconductor chips
We demonstrate the back-end integration of broadband, high-NA GaN
micro-lenses by micro-assembly onto non-native semiconductor substrates. We
developed a highly parallel micro-fabrication process flow to suspend micron
scale plano-convex lens platelets from 6" Si growth wafers and show their
subsequent transfer-printing integration. A growth process targeted at
producing unbowed epitaxial wafers was combined with optimisation of the
etching volume in order to produce flat devices for printing. Lens structures
were fabricated with 6 to 11 m diameter, 2 m height and
root-mean-squared surface roughness below 2 nm. The lenses were printed in a
vertically coupled geometry on a single crystalline diamond substrate and with
m-precise placement on a horizontally coupled photonic integrated circuit
waveguide facet. Optical performance analysis shows that these lenses could be
used to couple to diamond nitrogen vacancy centres at micron scale depths and
demonstrates their potential for visible to infrared light-coupling
applications.Comment: 16 pages, 14 figure
A novel microfiber wipe for delivery of active substances to human skin : clinical proof of concept
A novel technology for the delivery of active substances to the skin based on microfibers loaded with dried active substances was developed. The objective of this work was to demonstrate deposition of the active substances on the skin including concurrent cleansing properties of the wipe. As model active substance to measure deposition capacity Niacinamide was used and as parameter to measure cleansing capacities of the wipe squalene uptake was measured. Wipes loaded with niacinamide were used in the face and the forearm of 25 subjects. By means of Raman spectrometry the deposited niacinamide was analyzed before and after application. Wipes used on the face were analyzed for squalene to assess skin cleansing properties and for residual niacinamide. Forearm analysis including placebo and verum on left and right arm respectively was performed to rule out changes of the skin through application of the tissue. Measured amounts of niacinamide from face application demonstrate statistically significant results in the study population. Analysis of the wipes used show a liberation of 28.3% of niacinamide from the wipes and an uptake of 1.7 mg squalene per wipe. Results from forearm application show statistically significant differences (p < 0.05) between placebo and active for the complete study population. Sub group analyses are significant for both gender and ethnicity for face and forearm analysis respectively. Results clearly demonstrate deposition of niacinamide on the skin and the cleansing properties of the wipe. The institutional review board approved this prospective study
Laser written nitrogen vacancy centers in diamond integrated with transfer print GaN solid immersion lenses
Laser-written Nitrogen Vacancy (NVâ) centers are combined with transfer-printed GaN micro-lenses to increase fluorescent light collection by reducing total internal reflection at the planar diamond interface. We find a 2x improvement of fluorescent light collection using a 0.95 NA air objective at room temperature, in agreement with FDTD simulations. The nature of the transfer print micro-lenses leads to better performance with lower Numerical Aperture (NA) collection, as confirmed by results with a 0.5NA air objective which show improvement greater than 5x. The approach is attractive for scalable integrated quantum technologies
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