4 results
Search Results
Now showing 1 - 4 of 4
- ItemA neutral low-coordinate heterocyclic bismuth-tin species(Cambridge : Soc., 2015) Hering-Junghans, C.; Schulz, A.; Villinger, A.The reaction of distannadiazane bearing bulky RAr*-groups (RAr* = C6H2{C(H)Ph2}2R-2,6,4; R = iPr, tBu) with ECl3 (E = Sb, Bi) was studied resulting in the isolation of previously unknown N,N-bis(dichloropnictino)amines (3) and a novel heterocyclic carbenoid bismuth species (4) bearing a Bi(III) and a Sn(IV) center. The structure and bonding was investigated by means of X-ray structure elucidations and DFT calculations.
- ItemDirect Observation of Deformation in Microgel Filtration([London] : Macmillan Publishers Limited, part of Springer Nature, 2019) Linkhorst, John; Rabe, Jonas; Hirschwald, Lukas T.; Kuehne, Alexander J. C.; Wessling, MatthiasColloidal filtration processes using porous membranes suffer from productivity loss due to colloidal matter retention and continuous build-up by the retained matter. Especially during filtration of soft matter, the deformation of the individual colloids that make up the filter cake may be significant; however, this deformation and its impact remain unresolved so far. Yet, understanding the deformation on the single colloid level as well as on the ensemble level is important to be able to deconvolute filter cake properties from resistance increase of the membrane either by simultaneous internal adsorption or blocking of pores. Here, we report on the compression of a filter cake by filtrating soft microgels in a microfluidic channel in front of a model membrane. To study the single colloid deformation amorphous and crystalline domains were built up in front of the membrane and visualized on-line using confocal fluorescence microscopy while adjusting the degree of permeation, i.e., the transmembrane flux. Results show locally pronounced asymmetric deformation in amorphous domains, while the microgels in colloidal crystals approached regular polyeder shape. Increasing the flux beyond the maximum colloid deformation results in non-isochoric microgel behavior. The presented methodology enables a realistic description of complex colloidal matter deposits during filtration.
- ItemDetermination of tip transfer function for quantitative MFM using frequency domain filtering and least squares method(London : Nature Publishing Group, 2019) Nečas, D.; Klapetek, P.; Neu, V.; Havlíček, M.; Puttock, R.; Kazakova, O.; Hu, X.; Zajíčková, L.Magnetic force microscopy has unsurpassed capabilities in analysis of nanoscale and microscale magnetic samples and devices. Similar to other Scanning Probe Microscopy techniques, quantitative analysis remains a challenge. Despite large theoretical and practical progress in this area, present methods are seldom used due to their complexity and lack of systematic understanding of related uncertainties and recommended best practice. Use of the Tip Transfer Function (TTF) is a key concept in making Magnetic Force Microscopy measurements quantitative. We present a numerical study of several aspects of TTF reconstruction using multilayer samples with perpendicular magnetisation. We address the choice of numerical approach, impact of non-periodicity and windowing, suitable conventions for data normalisation and units, criteria for choice of regularisation parameter and experimental effects observed in real measurements. We present a simple regularisation parameter selection method based on TTF width and verify this approach via numerical experiments. Examples of TTF estimation are shown on both 2D and 3D experimental datasets. We give recommendations on best practices for robust TTF estimation, including the choice of windowing function, measurement strategy and dealing with experimental error sources. A method for synthetic MFM data generation, suitable for large scale numerical experiments is also presented.
- ItemParticle movements provoke avalanche-like compaction in soft colloid filter cakes([London] : Macmillan Publishers Limited, part of Springer Nature, 2021) Lüken, Arne; Stüwe, Lucas; Lohaus, Johannes; Linkhorst, John; Wessling, MatthiasDuring soft matter filtration, colloids accumulate in a compressible porous cake layer on top of the membrane surface. The void size between the colloids predominantly defines the cake-specific permeation resistance and the corresponding filtration efficiency. While higher fluxes are beneficial for the process efficiency, they compress the cake and increase permeation resistance. However, it is not fully understood how soft particles behave during cake formation and how their compression influences the overall cake properties. This study visualizes the formation and compression process of soft filter cakes in microfluidic model systems. During cake formation, we analyze single-particle movements inside the filter cake voids and how they interact with the whole filter cake morphology. During cake compression, we visualize reversible and irreversible compression and distinguish the two phenomena. Finally, we confirm the compression phenomena by modeling the soft particle filter cake using a CFD-DEM approach. The results underline the importance of considering the compression history when describing the filter cake morphology and its related properties. Thus, this study links single colloid movements and filter cake compression to the overall cake behavior and narrows the gap between single colloid events and the filtration process.