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Lubricating greases were investigated by nuclear magnetic resonance/magnetic resonance imaging (NMR/MRI) to get insight into their structure and into their response to mechanical forces, which is related to bleeding and aging. The investigated greases are based on metallic soaps of fatty acids and oils, whereby LiOH is often used. These organic soaps act as thickeners and provide a network in which oils and their additives are embedded. Lubricating greases can thus be considered as a class of substances similar to oleogels or even hydrogels. Questions arise about translational mobility of guest molecules, mainly base oil, in these networks. Molecular structuring and interactions within the network of thickeners are of interest as they are related to macroscopic stability. Apart from NMR spectroscopy ( 1 H-, 7 Li- and 31 P-NMR), spectrally resolved relaxation and diffusion measurements are used for characterization. In addition, magic angle spinning (MAS)-NMR was combined with 1 H-MRI to investigate the impact of mechanical stress and swelling of lubricating greases., (© 2021 John Wiley & Sons, Ltd.)

Magnetic Resonance Imaging is a powerful tool for the investigation of a biofilms' physical structure determining mass transport behavior which is of major importance in biofilm research. The entire biofilm is imaged in situ non-invasively and non-destructively on a meso-scale. In this study, different contrast agents were applied to study the biofilm's properties with the focus on mass transport, which is achieved by varying the contrast agents with respect to their NMR and interaction properties. The spatio-temporal tracking of these cluster, molecular and particulate contrast agents in biofilms was achieved by T1-, T2-weighted and proton density images during short (20h) and long (14 d) term exposures. The best biofilm surface visualization was observed when applying a new high spin coordination cluster (Fe10Gd10) showing a high affinity to the biofilm's surface and a fast immobilization within minutes. Contrarily, the small molecular contrast agents show no immobilization and fully penetrated into the biofilm. A concentration equilibrium was observed which was confirmed in back diffusion experiments. Interactions between larger nanoparticulate contrast agents and the biofilm required hours to achieve immobilization. Thus, the penetration depth into the biofilm is predominantly size-dependent. Here, it is shown that biofilm surface interactions can be observed in situ and spatio-temporarily resolved. The reported methodology demonstrates a new means to explore mass transfer of various substances in biofilms., Statement of Significance: In biofilm research, the investigation of the biofilms' physical structure is of high relevance for the understanding of mass transport processes. However, commonly used imaging techniques for biofilm imaging such as CLSM or electron microscopy rarely visualize the real biofilm due to their invasiveness and destructiveness. Magnetic Resonance Imaging (MRI) represents the ideal tool to image the biofilm in situ, non-invasively and non-destructively with a spatial resolution of several 10μm. To gain specific structural and functional information, a variety of MRI contrast agents (molecular and particulate) was applied with different properties for the first time. Results elucidate the interactions between the biofilms' surface and the contrast agents and open a new field for biotechnological applications by functional contrast enhancement., (Copyright © 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.)

The application of engineered nanoparticles (ENP) such as iron-based ENP in environmental systems or in the human body inevitably raises the question of their mobility. This also includes aspects of product optimization and assessment of their environmental fate. Therefore, the key aim was to investigate the mobility of iron-based ENP in water-saturated porous media. Laboratory-scale transport experiments were conducted using columns packed with quartz sand as model solid phase. Different superparamagnetic iron oxide nanoparticles (SPION) were selected to study the influence of primary particle size (d(P)=20 nm and 80 nm) and surface functionalization (plain, -COOH and -NH2 groups) on particle mobility. In particular, the influence of natural organic matter (NOM) on the transport and retention behaviour of SPION was investigated. In our approach, a combination of conventional breakthrough curve (BTC) analysis and magnetic resonance imaging (MRI) to non-invasively and non-destructively visualize the SPION inside the column was applied. Particle surface properties (surface functionalization and resulting zeta potential) had a major influence while their primary particle size turned out to be less relevant. In particular, the mobility of SPION was significantly increased in the presence of NOM due to the sorption of NOM onto the particle surface resulting in a more negative zeta potential. MRI provided detailed spatially resolved information complementary to the quantitative BTC results. The approach can be transferred to other porous systems and contributes to a better understanding of particle transport in environmental porous media and porous media in technical applications., (Copyright © 2015 Elsevier B.V. All rights reserved.)

Biofilms on cylindrical carrier material originating from a lab-scale moving bed biofilm reactor (MBBR) were investigated by means of Magnetic Resonance Imaging (MRI). The aim of this study was to determine the local flow velocities at the inner face of the biofilm carrier. To get an insight into the mass transport processes, flow velocity maps of blank and with biofilm cultivated carriers were measured. A single carrier was placed in a tube in three different orientations and exposed to flow velocities of 0.21, 0.42, and 0.64 mm/s. The interplay of the biofilm morphology and the local flow pattern was then analyzed including the effect of the orientation of the carrier in relation to the upstream flow angle. Within this study, the biofilm carrier can be understood as an interconnected system of four sections in which the incoming fluid volume will be distributed depending on the biomass occupation and morphology. In sections with high biofilm occupation, the flow resistance is increased. Depending on the orientation of the carrier in the flow field, this effect leads to flow evasion through less covered sections showing higher flow velocities and consequently the risk of biofilm detachment. However, there was no clear correlation between biofilm coverage and flow ratio., (© 2014 Wiley Periodicals, Inc.)

Sedimentation of opaque suspensions of carbon black and lithium-iron-phosphate was investigated by spin-echo-based magnetic resonance imaging. Optical methods are usually applied to determine settling velocities, but are limited with respect to high concentrations and optical transparency. The presented method uses intensity data from the noninvasively measured magnetic resonance signal of the sample. The settling velocity is obtained from the evolution of the signal intensity profiles based on the contrast in 1H magnetic resonance imaging between particles and liquid. New insights into the sedimentation in opaque suspensions are provided, since the 1H images uncover the spatial distribution of the particles and its agglomerates, as well as the shape of the settling front. Additionally, the sedimentation was experimentally studied using a sedimentation balance, which gravimetrically measures the increase in mass fraction over time due to the settling of particles. By parallel usage of these two methods, the sedimentation processes of opaque suspensions of lithium-ion-battery electrode materials were investigated. The sedimentation balance covers high, technically relevant concentrations. Limiting factors of the methods are discussed, which are mainly signal intensity in the magnetic resonance imaging and the increasing viscosity of highly concentrated suspensions. [ABSTRACT FROM AUTHOR]

Ultrafiltration with ceramic hollow fiber membranes was investigated by compressed sensing rapid acquisition relaxation enhancement (CS‐RARE) magnetic resonance imaging (MRI) to characterize filtration mechanisms. Sodium alginate was used as a model substance for extracellular polymeric substances. Dependent on the concentration of divalent ions like Ca2+ in an aqueous alginate solution, the characteristics of the filtration change from concentration polarization to a gel layer. The fouling inside the membrane lumen could be measured by MRI with a CS‐RARE pulse sequence. Contrast agents have been used to get an appropriate contrast between deposit and feed. The lumen was analyzed quantitatively by exploring the membrane's radial symmetry, and the resulting intensity could be modeled. Thus, different fouling mechanisms could be distinguished. CS‐RARE‐MRI was proven to be an appropriate in situ tool to quantitatively characterize the deposit formation during in‐out filtration processes. The results were underlined by flux interruption experiments and length dependent studies, which make it possible to differentiate between gel layer or cake filtration and concentration polarization filtration processes. © 2018 American Institute of Chemical Engineers AIChE J, 64: 4039–4046, 2018 [ABSTRACT FROM AUTHOR]

Magnetic resonance imaging was used to study the impact of Ca 2+ on the fouling behavior of alginate in dead-end and cross-flow filtrations. In situ experiments were performed to measure alginate layer formation and flow behavior during filtration. It was found that magnetic resonance imaging allows for distinguishing different structures of the formed alginate layers. The structure of the alginate layer without the addition of Ca 2+ is a fluid and unordered concentration polarization layer, whereas a dense and stable gel layer is formed on the membrane's surface in case of the filtration of alginate with Ca 2+ . This was in good agreement with data of filtration experiments. To overcome the lack of contrast between alginate and surrounding water, the addition of specific contrast agents was necessary in the case of dead-end filtration. Using tagging methods, the flow profiles during dead-end filtrations were investigated, and it was shown that the addition of Ca 2+ not only influences the fouling layer structure, but also the flow behavior. Furthermore, cross-flow experiments were performed. Here, the outflow effect was successfully used as contrast mechanism. [ABSTRACT FROM AUTHOR]

Biofilm formation during ultrafiltration membrane operation was investigated by Compressed Sensing Magnetic Resonance Imaging (MRI), with tryptic soy broth included in the feed stream to stimulate microbial growth. Biofilm development was visualized as growing layer characterized by reduced T 1 relaxation time, and its progression as monitored by MRI was compared with classical integral filtration parameters such as permeate flux J , transmembrane pressure Δ p and permeability L p to document fouling behavior. Over three days of growth a change in the filtration process could be observed in both measurements, with L p decreasing dramatically over time as the surface-associated biofilm increased in thickness. Following cessation of filtration and the associated drop in Δ p , the biofilm detached from the lumen wall and dispersed throughout the feed channel. Compressed Sensing MRI velocity and intensity measurements facilitate fast imaging during filtration processes, providing new possibilities for the investigation of biofouling in filtration membranes. Image 1 • Biofouling in multichannel hollow fiber membranes is characterized in-situ by MRI. • Biofouling was stimulated with tryptic soy broth in the feed solution. • T 1 -contrast images track biofilm development inside the membrane channels. • Velocity images allow the characterization of flow during filtration. • Compressed Sensing (CS) considerably reduces measurement time. [ABSTRACT FROM AUTHOR]

Cross-flow membrane ultrafiltration of the polysaccharide sodium alginate in aqueous solution was investigated in polymeric Helix membranes by in-situ magnetic resonance imaging (MRI) non-invasively and non-destructively. MRI allows velocity and NMR intensity measurements during filtration. In the present case and under the conditions used in the experiments, signal intensity is mainly generated by 1H of water. Lower intensities can therefore be understood as a measure for material accumulation. Compressed sensing allows faster data acquisition, enabling a reliable, time resolved measurement of the ultrafiltration progress. Even under cross-flow filtration conditions, the membrane filtration is impaired by the increasing filtration resistance due to gel layer formation during the filtration of aqueous sodium alginate with CaCl 2. The Helix membrane has an additional helical ridge along the membrane wall to provide fouling inhibition, resulting in a complex three-dimensional flow field that was measured via compressed sensing MRI. Furthermore, the behavior of the deposit was classified more precisely by backwashing in the Helix membrane. Summarizing, the flow field, the deposit formation during cross-flow filtration in a Helix membrane and its backwashing was monitored and investigated by fast MRI methods. [Display omitted] • In-situ cross-flow ultrafiltration in a polymeric Helix membrane with sodium alginate. • Compressed sensing magnetic resonance imaging to measure deposit structure and flow. • Dedicated image processing and modelling of signal intensity data. • Gel layer formation and backwashing of sodium alginate with Ca2+. [ABSTRACT FROM AUTHOR]