Combined nuclear magnetic resonance methods in quality control of lubricants in green energy production.

NMR methods were applied for lubricant analysis. Different factors influence the real aging of lubricants on diverse length scales and are captured by NMR. Chemical conversion of additives is addressed by NMR spectroscopy. High-field NMR experiments allow the identification and quantification of chemical components and are transferred to benchtop devices. Molecular dynamics and contaminations like fuel or abrasion are addressed via NMR relaxation and diffusion. Quality parameters were extracted via suitable data analysis of NMR raw data, which allow the detection of aging and indicate changes in the oil composition. At the same time, the methodology is optimized to the conditions in quality control. The feasibility is shown the example of a series of lubricants from applications in regenerative energy production, namely, wind turbine oils and biogas motor oils.

NMR in Battery Anode Slurries with a V-Shaped Sensor.

Inline analytics in industrial processes reduce operating costs and production rejection. Dedicated sensors enable inline process monitoring and control tailored to the application of interest. Nuclear Magnetic Resonance is a well-known analytical technique but needs adapting for low-cost, reliable and robust process monitoring. A V-shaped low-field NMR sensor was developed for inline process monitoring and allows non-destructive and non-invasive measurements of materials, for example in a pipe. In this paper, the industrial application is specifically devoted to the quality control of anode slurries in battery production. The characterization of anode slurries was performed with the sensor to determine chemical composition and detect gas inclusions. Additionally, flow properties play an important role in continuous production processes. Therefore, the in- and outflow effects were investigated with the V-shaped NMR sensor as a basis for the future determination of slurry flow fields.

Inline NMR via a Dedicated V-Shaped Sensor.

Process monitoring and control require dedicated and reliable measures which reflect the status of the process under investigation. Although nuclear magnetic resonance is known to be a versatile analytical technique, it is only seldomly found in process monitoring. Single-sided nuclear magnetic resonance is one well known approach for being applied in process monitoring. The dedicated V-sensor is a recent approach that allows the inline investigation of materials in a pipe non-destructively and non-invasively. An open geometry of the radiofrequency unit is realized using a tailored coil, enabling the sensor to be applied for manifold mobile applications in in-line process monitoring. Stationary liquids were measured, and their properties were integrally quantified as the basis for successful process monitoring. The sensor, in its inline version, is presented along with its characteristics. An exemplary field of application is battery production in terms of anode slurries; thus, the first results on graphite slurries will demonstrate the added value of the sensor in process monitoring.

Nuclear magnetic resonance/magnetic resonance imaging on lubricating greases: Observation of bleeding and aging.

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.

Investigation of the surfactant distribution in oil-in-water emulsions during the crystallization of the dispersed phase via nuclear magnetic resonance relaxometry and diffusometry.

The crystallization of melt emulsions is of great interest to the food, cosmetic, and pharmaceutical industries. Surfactants are used in emulsions and suspensions to stabilize the dispersed phase; thus, questions arise about the liquid-liquid and solid-liquid interfaces of the droplets or particles and the distribution of the surfactant in the different phases (continuous and dispersed phase, interface). Nuclear magnetic resonance relaxation and diffusion measurements revealed that the internal and rotational mobility of surfactant molecules at the liquid-liquid interface decreases with increasing droplet sizes. Additionally, solid-liquid interfaces have fewer surfactants than liquid-liquid interfaces as a result of the desorption of the surfactant molecules during the crystallization of the droplets. Relaxation rates of surfactant molecules in aqueous solution as single molecules, micelles, and at the liquid-liquid and solid-liquid interface are analyzed for the first time.

Dedicated NMR sensor to analyze relaxation and diffusion in liquids and its application to characterize lubricants.

A dedicated nuclear magnetic resonance (NMR) sensor was designed for the analysis of liquids. The magnets are arranged in a V shape, creating a spatially dependent magnetic field in the gap. Measurements of samples with diverse diameters are possible underdefined magnetic field gradients at a given position. The magnet thus combines properties of single sided NMR with high static magnetic field gradients and classical time domain (TD) devices with lower to almost zero gradients. The sensor can easily be adapted to the requirements of the considered investigation; probes can be customized. On the example of lubricants and their aging, the added value and applicability of this sensor in quality control are highlighted in this publication. Relaxation and diffusion were measured by Carr-Purcell-Meiboom-Gill (CPMG) while varying the echo time τe and quantified via numerical modeling. Especially, relaxation shows a high sensitivity towards aging of lubricants such as particulate abrasion and changes in molecular dynamics induced, for example, by additive depletion. The applicability of this NMR sensor in quality control is demonstrated on the example of engine and transmission oils as well as of lubrication greases.

Low-field NMR for quality control on oils.

Oil is a prominent, but multifaceted material class with a wide variety of applications. Technical oils, crude oils as well as edibles are main subclasses. In this review, the question is addressed how low-field NMR can contribute in oil characterization as an analytical tool, mainly with respect to quality control. Prerequisite in the development of a quality control application, however, is a detailed understanding of the oils and of the measurement. Low-field NMR is known as a rich methodical toolbox that was and is explored and further developed to address questions about oils, their quality, and usability as raw materials, during production and formulation as well as in use.

In situ measurement of deposit layer formation during skim milk filtration by MRI.

Filtration and separation via membranes are key processes in food processing. One major application of membrane filtration is in the dairy industry, aiming for the separation of different milk proteins. The various chemical components of milk possess different physiochemical properties and can be used most effectively in food processing if they are separately available and remain in their native state. Microfiltration of skim milk allows a fractionation of the milk proteins casein and whey by size. A deposit is formed on the membrane surface mainly but not exclusively by micellar casein proteins during filtration. Membrane pore blockage by whey proteins and fouling occur during membrane filtration, negatively affecting the yield of the whey protein fraction. Skim milk filtration and the deposit layer formation were measured time and spatially resolved by in situ magnetic resonance imaging (MRI). The nature of the fouling layer was investigated during dead-end filtration in ceramic hollow fiber membranes. MRI was used to further clarify the influence of operating conditions on separation and filtration mechanisms that are responsible for growth of the fouling layer and its reversibility. The MRI measurements were analyzed for a detailed description of skim milk filtration by modeling the signal intensity distribution.

Instability Mechanisms of Water-in-Oil Nanoemulsions with Phospholipids: Temporal and Morphological Structures.

Many food preparations, pharmaceuticals, and cosmetics use water-in-oil (W/O) emulsions stabilized by phospholipids. Moreover, recent technological developments try to produce liposomes or lipid coated capsules from W/O emulsions, but are faced with colloidal instabilities. To explore these instability mechanisms, emulsification by sonication was applied in three cycles, and the sample stability was studied for 3 h after each cycle. Clearly identifiable temporal structures of instability provide evidence about the emulsion morphology: an initial regime of about 10 min is shown to be governed by coalescence after which Ostwald ripening dominates. Transport via molecular diffusion in Ostwald ripening is commonly based on the mutual solubility of the two phases and is therefore prohibited in emulsions composed of immiscible phases. However, in the case of water in oil emulsified by phospholipids, these form water-loaded reverse micelles in oil, which enable Ostwald ripening despite the low solubility of water in oil, as is shown for squalene. As is proved for the phospholipid dipalmitoylphosphatidylcholine (DPPC), concentrations below the critical aggregation concentration (CAC) form monolayers at the interfaces and smaller droplet sizes. In contrast, phospholipid concentrations above the CAC create complex multilayers at the interface with larger droplet sizes. The key factors for stable W/O emulsions in classical or innovative applications are first, the minimization of the phospholipids' capacity to form reversed micelles, and second, the adaption of the initial phospholipid concentration to the water content to enable an optimized coverage of phospholipids at the interfaces for the intended drop size.

Adsorption of phospholipids at oil/water interfaces during emulsification is controlled by stress relaxation and diffusion.

Adsorption of phosphatidylcholines at oil/water interfaces strongly deviates from spread monolayers at air/water surfaces. Understanding its nature and consequences could vastly improve applications in medical nanoemulsions and biotechnologies. Adsorption kinetics at interfaces of water with different oil phases were measured by profile analysis tensiometry. Adsorption kinetics for 2 different phospholipids, DPPC and POPC, as well as 2 organic phases, squalene and squalane, show that formation of interfacial monolayers is initially dominated by stress-relaxation in the first minutes. Diffusion only gradually contributes to a decrease in interfacial tension at later stages of time and higher film pressures. The results can be applied for the optimization of emulsification protocols using mechanical treatments. Emulsions using phospholipids with unsaturated fatty acids are dominated much more strongly by stress-relaxation and cover interfaces very fast compared to those with saturated fatty acids. In contrast, phospholipid layers consisting of saturated fatty acids converge faster towards the equilibrium than those with unsaturated fatty acids.

Interactions between Phospholipids and Organic Phases: Insights into Lipoproteins and Nanoemulsions.

The adsorption of phosphatidylcholines (PCs), dissolved in squalene or squalane as an organic phase, was studied at the interface with water. Using profile analysis tensiometry, the equilibrium adsorption isotherms, minimum molecular interfacial areas, and solubility limits were derived. For squalene, differences in PC solubility and interfacial adsorption were found, depending on PC saturation. Compared to saturated PCs, unsaturated PCs showed a 3-fold-lower interfacial density but up to a 28-fold-higher critical aggregation concentration (CAC). In addition, the solubility limit of unsaturated PC in squalene and in its saturated form squalane diverged by a factor of 739. These findings provided evidence for steric repulsion or π-π interactions of π bonds in both solvent and solute or both effects acting complementarily. In squalane, low solubilities but high interfacial densities were found for all investigated PCs. Changes in fatty acid chain lengths showed that the influence of the increases in entropy and enthalpy on solubility is much smaller than solvent/solute interactions. Oxidation products of squalene lowered the interfacial tension, but increasing concentrations of PC expelled them from the interface. The CAC of saturated PC was increased by oxidation products of squalene whereas that of unsaturated PCs was not. Our findings indicate that the oxidation of triglycerides in lipoprotein cores can lead to increased solubility of saturated phospholipids covering the lipoproteins, contributing to destabilization, coalescence, and terminally the formation of atherosclerotic plaques. The consideration of solvent/solute interactions in molecular modeling may contribute to the interfacial tension and the corresponding kinetic or thermodynamic stability of lipoproteins. Measured areas per molecule prove that PCs form monolayers of different interfacial densities at the squalene/water interface but multilayers at the squalane/water interface. These findings showed that combinations of solvent or solute saturation affect the outcome for nanoemulsions forming either expanded or condensed monolayers or multilayers.

Iron as Recyclable Metal Fuel: Unraveling Oxidation Behavior and Cyclization Effects Through Thermogravimetric Analysis, Wide-Angle X-ray Scattering and Mössbauer Spectroscopy.

The carbon-free chemical storage and release of renewable energy is an important task to drastically reduce CO2 emissions. The high specific energy density of iron and its recyclability makes it a promising storage material. Energy release by oxidation with air can be realized by the combustion of micron-sized iron powders in retro-fitted coal fired power plants and in fixed-bed reactors under milder conditions. An experimental parameter study of iron powder oxidation with air was conducted based on thermogravimetric analysis in combination with wide-angle X-ray scattering and Mössbauer spectroscopy. In agreement with literature the oxidation was found to consist of a very fast initial oxidation of the outer particle layer followed by much slower oxidation due to diffusion of iron ions through the Fe2O3/Fe3O4 layer being the rate-limiting step. Scanning electron microscopy analysis of the iron particle before and after oxidation reveal a strong particle morphology transformation. This impact on the reaction was studied by cyclization experiments. Up to 10 oxidation-reduction cycles show that both, oxidation and reduction rates, increase strongly with cycling due to increased porosity.

Spray Flame Synthesis and Multiscale Characterization of Carbon Black-Silica Hetero-Aggregates.

The increasing demand for lithium-ion batteries requires constant improvements in the areas of production and recycling to reduce their environmental impact. In this context, this work presents a method for structuring carbon black aggregates by adding colloidal silica via a spray flame with the goal of opening up more choices for polymeric binders. The main focus of this research lies in the multiscale characterization of the aggregate properties via small-angle X-ray scattering, analytical disc centrifugation and electron microscopy. The results show successful formation of sinter-bridges between silica and carbon black leading to an increase in hydrodynamic aggregate diameter from 201 nm to up to 357 nm, with no significant changes in primary particle properties. However, segregation and coalescence of silica particles was identified for higher mass ratios of silica to carbon black, resulting in a reduction in the homogeneity of the hetero-aggregates. This effect was particularly evident for silica particles with larger diameters of 60 nm. Consequently, optimal conditions for hetero-aggregation were identified at mass ratios below 1 and particle sizes around 10 nm, at which homogenous distributions of silica within the carbon black structure were achieved. The results emphasise the general applicability of hetero-aggregation via spray flames with possible applications as battery materials.

Monolayer/Bilayer Equilibrium of Phospholipids in Gel or Liquid States: Interfacial Adsorption via Monomer or Liposome Diffusion?

Phospholipids (PLs) are widely used in the pharma industry and a better understanding of their behavior under different conditions is helpful for applications such as their use as medical transporters. The transition temperature Tm affects the lipid conformation and the interfacial tension between perfluoroperhydrophenanthrene (PFP) and an aqueous suspension of 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC), 1,2-distearoyl-sn-glycero-3-phosphatidylcholine (DSPC), as well as a mixture of these PLs with cholesterol. Interfacial tensions were measured with the Du Noüy ring at quasi-equilibrium; the area per molecule was calculated according to the Gibbsian approach and a time-dependent tension gradient. Results show that the time tε to reach quasi-equilibrium was shorter when the temperature was above Tm, indicating a faster adsorption process (tε,DPPC,36 °C = 48 h, tε,DPPC,48 °C = 24 h) for PL in the liquid crystalline state than in the gel state (T < Tm). In addition, concentration-dependent results of the interfacial tension revealed that above the respective Tm and at all concentrations c > 0.1 mM, the average minimum interfacial tension for DPPC and DSPC (14.1 mN/m and 15.3 mN/m) does not differ significantly between those two lipids. Equilibrium between monolayers and bilayers shows that for T < Tm, surface pressures ∏ ≈ 31 mN/m are reached while for T > Tm, ∏ ≈ 41 mN/m. Mixtures with cholesterol only reach ∏ ≤ 31 mN/m Tm, with no significant difference between the two PLs. The higher interfacial tension of the mixture indicates stabilization of the liposomal conformation in the aqueous phase by the addition of cholesterol. The high diffusion coefficients show that adsorption is mainly based on liposomes.

3D Printing Hierarchically Nano-Ordered Structures.

Natural materials are composed of a limited number of molecular building blocks and their exceptional properties are governed by their hierarchical structure. However, this level of precision is unattainable with current state-of-the-art materials for 3D printing. Herein, new self-assembled printable materials based on block copolymers (BCPs) enabling precise control of the nanostructure in 3D are presented. In particular, well-defined BCPs consisting of poly(styrene) (PS) and a polymethacrylate-based copolymer decorated with printable units are selected as suitable self-assembled materials and synthesized using controlled radical polymerization. The synthesized library of BCPs are utilized as printable formulations for the fabrication of complex 3D microstructures using two-photon laser printing. By fine-tuning the BCP composition and solvent in the formulations, the fabrication of precise 3D nano-ordered structures is demonstrated for the first time. A key point of this work is the achievement of controlled nano-order within the entire 3D structures. Thus, imaging of the cross-sections of the 3D printed samples is performed, enabling the visualization also from the inside. The presented versatile approach is expected to create new avenues for the precise design of functional polymer materials suitable for high-resolution 3D printing exhibiting tailor-made nanostructures.

Particle and Phase Analysis of Combusted Iron Particles for Energy Storage and Release.

The combustion of metal fuels as energy carriers in a closed-cycle carbon-free process is a promising approach for reducing CO2 emissions in the energy sector. For a possible large-scale implementation, the influence of process conditions on particle properties and vice versa has to be well understood. In this study, the influence of different fuel-air equivalence ratios on particle morphology, size and degree of oxidation in an iron-air model burner is investigated by means of small- and wide-angle X-ray scattering, laser diffraction analysis and electron microscopy. The results show a decrease in median particle size and an increase in the degree of oxidation for leaner combustion conditions. The difference of 1.94 µm in median particle size between lean and rich conditions is twentyfold greater than the expected amount and can be connected to an increased intensity of microexplosions and nanoparticle formation for oxygen-rich atmospheres. Furthermore, the influence of the process conditions on the fuel usage efficiency is investigated, yielding efficiencies of up to 0.93. Furthermore, by choosing a suitable particle size range of 1 to 10 µm, the amount of residual iron content can be minimized. The results emphasize that particle size plays a key role in optimizing this process for the future.

Characterization of Fractal Structures by Spray Flame Synthesis Using X-ray Scattering.

In this work, we take on an in-depth characterization of the complex particle structures made by spray flame synthesis. Because of the resulting hierarchical aggregates, very few measurement techniques are available to analyze their primary particle and fractal properties. Therefore, we use small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) to investigate the influence of the precursor concentration on the fractal structures of zirconia nanoparticles. The combination of information gained from these measurement results leads to a detailed description of the particle system, including the polydispersity and size distribution of the primary particles. Based on our findings, unstable process conditions could be identified at low precursor concentrations resulting in the broadest size distribution of primary particles with rough surfaces. Higher precursor concentrations lead to reproducible primary particle sizes almost independent of the initial precursor concentration. Regarding the fractal properties, the typical shape of aggregates for aerosols is present for the investigated range of precursor concentrations. In conclusion, the consistent results for SAXS and TEM show a conclusive characterization of a complex particle system, allowing for the identification of the underlying particle formation mechanism.

Separation of Microplastic Particles from Sewage Sludge Extracts Using Magnetic Seeded Filtration.

Microplastic particles (MP) are efficiently retained in wastewater treatment plants and enriched in sewage sludge. For monitoring MP contents in wastewater systems, sewage sludge is thus well suited, but also requires an isolation of MP from the sludge matrix, as other sewage sludge components may interfere with the MP identification and quantification. Although organic matter in sludge samples can be removed through acid and enzymatic digestion procedures, cellulose - mainly from toilet paper - remains in the digests, due to its high chemical resistivity and similar density to MP. We apply the separation concept of magnetic seeded filtration to isolate MP through selective hetero-agglomeration with magnetic seed particles. MP and cellulose differ in their hydrophobic properties and we investigate to what extent these differences can be exploited to selectively form MP-magnetite hetero-agglomerates in the presence of cellulose. These hetero-agglomerates are subsequently separated using a magnet. Five MP types (Polyethylene terephthalate (PET), polypropylene (PP), low density polyethylene (LDPE), polyvinyl chloride (PVC) and polystyrene (PS)) and cellulose particles were mixed in different combinations with both hydrophilic and hydrophobic (silanized) magnetite particles. PET, PP, LDPE and PS only poorly agglomerated with pristine (hydrophilic) magnetite, but efficiently formed hetero-agglomerates with hydrophobic magnetite and were successfully removed from suspensions ( 80 - 100 % ). PVC agglomerated more efficiently with pristine than with hydrophobic magnetite and cellulose only agglomerated to a limited extent with either hydrophilic or hydrophobic magnetite, resulting in a high process selectivity. Results from experiments conducted at different ionic strengths and with hydrophilic and hydrophobic magnetite suggests that the agglomeration process was dominated by hydrophobic interactions. Enzymatic and oxidative treatment of the MP only marginally affected the separation efficiencies and (treated) MP spiked to sewage sludge extracts were successfully recovered using magnetic seeded filtration.

Real-Time Modeling of Volume and Form Dependent Nanoparticle Fractionation in Tubular Centrifuges.

A dynamic process model for the simulation of nanoparticle fractionation in tubular centrifuges is presented. Established state-of-the-art methods are further developed to incorporate multi-dimensional particle properties (traits). The separation outcome is quantified based on a discrete distribution of particle volume, elongation and flatness. The simulation algorithm solves a mass balance between interconnected compartments which represent the separation zone. Grade efficiencies are calculated by a short-cut model involving material functions and higher dimensional particle trait distributions. For the one dimensional classification of fumed silica nanoparticles, the numerical solution is validated experimentally. A creation and characterization of a virtual particle system provides an additional three dimensional input dataset. Following a three dimensional fractionation case study, the tubular centrifuge model underlines the fact that a precise fractionation according to particle form is extremely difficult. In light of this, the paper discusses particle elongation and flatness as impacting traits during fractionation in tubular centrifuges. Furthermore, communications on separation performance and outcome are possible and facilitated by the three dimensional visualization of grade efficiency data. Future research in nanoparticle characterization will further enhance the models use in real-time separation process simulation.

Charge Transport and Glassy Dynamics in Blends Based on 1-Butyl-3-vinylbenzylimidazolium Bis(trifluoromethanesulfonyl)imide Ionic Liquid and the Corresponding Polymer.

Charge transport, diffusion properties, and glassy dynamics of blends of imidazolium-based ionic liquid (IL) and the corresponding polymer (polyIL) were examined by Pulsed-Field-Gradient Nuclear Magnetic Resonance (PFG-NMR) and rheology coupled with broadband dielectric spectroscopy (rheo-BDS). We found that the mechanical storage modulus (G') increases with an increasing amount of polyIL and G' is a factor of 10,000 higher for the polyIL compared to the monomer (GIL'= 7.5 Pa at 100 rad s-1 and 298 K). Furthermore, the ionic conductivity (σ0) of the IL is a factor 1000 higher than its value for the polymerized monomer with 3.4×10-4 S cm-1 at 298 K. Additionally, we found the Haven Ratio (HR) obtained through PFG-NMR and BDS measurements to be constant around a value of 1.4 for the IL and blends with 30 wt% and 70 wt% polyIL. These results show that blending of the components does not have a strong impact on the charge transport compared to the charge transport in the pure IL at room temperature, but blending results in substantial modifications of the mechanical properties. Furthermore, it is highlighted that the increase in σ0 might be attributed to the addition of a more mobile phase, which also possibly reduces ion-ion correlations in the polyIL.