Self-diffusion Measurements Research Articles

Probing the potential of type V Deep eutectic solvents as sustainable electrolytes

The increasing interest within the scientific community in environmentally friendly solvents has led to a focus on Deep Eutectic Solvents (DES), which have natural components. DES are viewed as alternatives to traditional organic solvents and have the potential to be used as electrolytes. For the first time, transport properties of four Type V Deep Eutectic Salt Solutions (DESS) were accessed to investigate the potential of this technology, selecting precursors ranked as excellent in Eco-Scale metrics. The DESS were composed of terpene and trioctylphosphine oxide (TOPO), and varying concentrations of lithium bis(trifluoromethane)sulfonimide (LiTFSI), and their properties were assessed through self-diffusion, viscosity, density, and conductivity measurements. While Type V DESS are capable of dissolving significant amounts of LiTFSI (up to 30 % molar), their ionic conductivity is low, with values ranging from 3.6·10−3 to 9.3·10−2 mS·cm−1 at 25 °C, thus limiting their suitability as electrolytes, for instance, for lithium-ions batteries applications. Similar diffusion coefficients for Li+ and TFSI− ions suggest the formation of long-lived ion pairs moving as a neutral species. Therefore, future research aims to introduce additives to disrupt contact ion pairs and enhance transport properties, leveraging the sustainable appeal of DES and their use in advanced energy storage technologies.

Influence of interstitial cluster families on post-synthesis defect manipulation and purification of oxides using submerged surfaces.

Injection of interstitial atoms by specially prepared surfaces submerged in liquid water near room temperature offers an attractive approach for post-synthesis defect manipulation and isotopic purification in device structures. However, this approach can be limited by trapping reactions that form small defect clusters. The compositions and dissociation barriers of such clusters remain mostly unknown. This communication seeks to address this gap by measuring the dissociation energies of oxygen interstitial traps in rutile TiO2 and wurtzite ZnO exposed to liquid water. Isotopic self-diffusion measurements using 18O, combined with progressive annealing protocols, suggest the traps are small interstitial clusters with dissociation energies ranging from 1.3 to 1.9eV. These clusters may comprise a family incorporating various numbers, compositions, and configurations of O and H atoms; however, in TiO2, native interstitial clusters left over from initial synthesis may also play a role. Families of small clusters are probably common in semiconducting oxides and have several consequences for post-synthesis defect manipulation and purification of semiconductors using submerged surfaces.

Gas self-diffusion in different local environments of mixed-matrix membranes as a function of UiO-66-NH2 metal–organic framework loading

This work focuses on quantification of microscopic self-diffusion of gas molecules in mixed-matrix membranes (MMMs) formed by dispersing UiO-66-NH2 metal–organic framework (MOF) crystals in 6FDA-Durene polyimide. Self-diffusion measurements were performed by 13C pulsed field gradient nuclear magnetic resonance (PFG NMR) for pure CO2 and CH4 with the spatial resolution in the range of 0.5–24 μm and for different MOF loadings between 12.5 and 50 weight percent. Diffusion measurements performed for each gas in the MMM with the lowest MOF loading of 12.5 weight percent yielded a single diffusivity for all measured diffusion times corresponding to a diffusion under the condition of a fast exchange between the UiO-66-NH2 crystals and the surrounding polymer phase. However, as the UiO-66-NH2 loading was increased, two molecular ensembles were observed for both CO2 and CH4: 1) an ensemble corresponding to diffusion inside UiO-66-NH2 crystals and through the MOF–polymer interfaces, and 2) an ensemble corresponding to diffusion mainly in the polymer phase of the MMMs. This behavior can be explained by the formation of MOF clusters at higher MOF loadings. Quantification of the intra-cluster diffusivity, average cluster size, and the dependence of these properties on the MOF loading are presented and discussed. The reported measurements can serve as a framework to quantify discrete microscopic diffusion characteristics and sizes of interconnected MOF clusters in MMMs as MOF loading increases to reach the desired outcome of gas percolation over a spanning MOF cluster, viz a cluster of interconnected MOF crystals spanning an entire MMM.

Wavenumber-dependent dynamic light scattering optical coherence tomography measurements of collective and self-diffusion

We demonstrate wavenumber-dependent DLS-OCT measurements of collective and self-diffusion coefficients in concentrated silica suspensions across a broad q-range, utilizing a custom home-built OCT system. Depending on the sample polydispersity, either the collective or self-diffusion is measured. The measured collective-diffusion coefficient shows excellent agreement with hard-sphere theory and serves as an effective tool for accurately determining particle sizes. We employ the decoupling approximation for simultaneously measuring collective and self-diffusion coefficients, even in sufficiently monodisperse suspensions, using a high-speed Thorlabs OCT system. This enables particle size and volume fraction determination without the necessity of wavenumber-dependent measurements. We derive a relationship between the particle number-based polydispersity index and the ratio of self and collective mode amplitudes in the autocorrelation function and utilize it to measure the particle number-based polydispersity index. Notably, the polydispersity determined in this manner demonstrates improved sensitivity to smaller particle sizes compared to the standard intensity-based DLS cumulant analysis performed on dilute samples.

Measurement of crude oil emulsion instability using magnetic resonance and magnetic resonance imaging

Emulsion stability is important in many environmental and industrial applications. Unstable emulsions tend to have a layered structure which will evolve in space and time. Magnetic Resonance (MR) is a nondestructive method that can be used to study emulsion instability based on relaxation times (T1, T2), and/or diffusion (D). The bulk transverse relaxation lifetime (T2) is the most useful parameter for analysis. Since breaking of emulsions creates different layers and phases, spatially resolved T2 data is more valuable than bulk whole sample data. Previous literature studies were principally based on bulk T1, T2 or self-diffusion measurements without spatial resolution. In this study, for the first time, spatially resolved T2 distributions were used to examine oil and water behavior during emulsion breaking.Diluted bitumen was used as the oil phase in a synthetic emulsion. Measurements undertaken included spatially resolved T2 distribution measurements and T1-T2 relaxation correlation measurements. The results reveal changes in the relaxation times of oil and water caused by changes in the dynamics of the water and oil during emulsion breaking. In each layer of the sample, comparing peak T2 values with bulk T2 values of different components gives an insight into phase environments. Water and oil content in each layer was resolved by using peak areas of the T2 distribution. The results of T2 distribution imaging were consistent with optical microscopy images, which showed W/O emulsions in the oil dominant region and complex W/O/W emulsions in the water dominant region of the sample. With the above information one can obtain full spatial and temporal information on evolving phases as well as kinetics of phase dynamics in emulsion breaking.

Effects of adventitious impurity adsorption on oxygen interstitial injection rates from submerged TiO2(110) and ZnO(0001) surfaces

Low bond coordination of surface atoms facilitates the injection of oxygen interstitial atoms into the bulk near room temperature from the clean surfaces of semiconducting metal oxides when exposed to liquid water, opening new prospects for postsynthesis defect engineering and isotopic fractionation. The injection rate and penetration depth vary considerably under identical experimental conditions, however, with the adsorption of adventitious carbon suggested as the cause. For water-submerged rutile TiO2(110) and wurtzite ZnO(0001), this work bolsters and refines that hypothesis by combining the isotopic self-diffusion measurements of oxygen with characterization by x-ray photoelectron spectroscopy and atomic force microscopy. Adventitious carbon likely diminishes injection rates by poisoning small concentrations of exceptionally active surface sites that either inject O or dissociate adsorbed OH to injectable O. These effects propagate into the penetration depth via the progressive saturation of Oi traps near the surface, which occurs less extensively as the injected flux decreases.

Structural and dynamic heterogeneity in associative networks formed by artificially engineered protein polymers.

This work investigates static gel structure and cooperative multi-chain motion in associative networks using a well-defined model system composed of artificial coiled-coil proteins. The combination of small-angle and ultra-small-angle neutron scattering provides evidence for three static length scales irrespective of protein gel design which are attributed to correlations arising from the blob length, inter-junction spacing, and multi-chain density fluctuations. Self-diffusion measurements using forced Rayleigh scattering demonstrate an apparent superdiffusive regime in all gels studied, reflecting a transition between distinct "slow" and "fast" diffusive species. The interconversion between the two diffusive modes occurs on a length scale on the order of the largest correlation length observed by neutron scattering, suggesting a possible caging effect. Comparison of the self-diffusive behavior with characteristic molecular length scales and the single-sticker dissociation time inferred from tracer diffusion measurements supports the primarily single-chain mechanisms of self-diffusion as previously conceptualized. The step size of the slow mode is comparable to the root-mean-square length of the midblock strands, consistent with a single-chain walking mode rather than collective motion of multi-chain aggregates. The transition to the fast mode occurs on a timescale 10-1000 times the single-sticker dissociation time, which is consistent with the onset of single-molecule hopping. Finally, the terminal diffusivity depends exponentially on the number of stickers per chain, further suggesting that long-range diffusion occurs by molecular hopping rather than sticky Rouse motion of larger assemblies. Collectively, the results suggest that diffusion of multi-chain clusters is dominated by the single-chain pictures proposed in previous coarse-grained modeling.

Benefits of Chemometric and Raman Spectroscopy Applied to the Kinetics of Setting and Early Age Hydration of Cement Paste.

The addition of water is used to past by internal post-curing of hardening cement. Hydration and curing of cementitious are widely identified by non-destructive 1H nuclear magnetic resonance (NMR) measurements of transverse relaxation time and self-diffusion. However, those non-destructive analytical methodologies do not give a truly chemical characterization of the cement matrix during the hydration and curing process. Indeed, the NMR studies only the water dynamics of hydrating cement with internal post-curing. Recent research indicated chemometrics coupled with Raman spectroscopy allows for a better understanding of chemical processes. Recent advances in computing gave industries and research centers the opportunity to generate cost effective data. In this work, an original method is presented, which uses both a data analysis and a non-invasive, non-destructive Raman monitoring of the hydration reaction of a Portland cement. Data was then analyzed by means of chemometrics methods (principal components analysis (PCA), independent components analysis (ICA), and multivariate curve resolution-alternated least-squares (MCR-ALS) with SIMPLe-to-use Interactive Self-modelling Mixture Analysi (SIMPLISMA) and Orthogonal Projection Approach (OP initialization). Results were compared to the ones obtained with thermogravimetric analysis of this cement paste. Besides the consistency of results from both analytical measurements, chemometrics coupled to Raman spectroscopy accurately revealed the details of the setting without any samples collection. The acquisition frequency allowed a proper identification of the occurrence of each of the various phases involved in the hydration and setting process.

Strong Isotopic Fractionation of Oxygen in TiO2 Obtained by Surface-Enhanced Solid-State Diffusion.

Isotopically pure semiconductors have important applications for cooling electronic devices and quantum computing and sensing. Raw materials of sufficiently high isotopic purity are expensive and difficult to obtain; therefore, a post-synthesis method for removing isotopic impurities would be valuable. Through isotopic self-diffusion measurements of oxygen in rutile TiO2 single crystals immersed in water, we demonstrate fractionation of 18O by a factor of 3 below natural abundance in a near-surface region up to 10 nm wide. The submerged surface injects O interstitials that displace lattice 18O deeper into the solid as a result of the statistics of interstitialcy-mediated diffusion combined with steep chemical gradients of O interstitials. Slightly acidic and slightly basic liquid solutions both enhance the fractionation and affect the details of isotopic profile shapes through several chemical and physical mechanisms.

1H LF-NMR Self-Diffusion Measurements for Rapid Monitoring of an Edible Oil's Food Quality with Respect to Its Oxidation Status.

The food quality of edible oils is dependent on basic chemical and structural changes that can occur by oxidation during preparation and storage. A rapid and efficient analytical method of the different steps of oil oxidation is described using a time-domain nuclear magnetic resonance (TD-NMR) sensor for measuring signals related to the chemical and physical properties of the oil. The degree of thermal oxidation of edible oils at 80 °C was measured by the conventional methodologies of peroxide and aldehyde analysis. Intact non-modified samples of the same oils were more rapidly analyzed for oxidation using a TD-NMR sensor for 2D T1-T2 and self-diffusion (D) measurements. A good linear correlation between the D values and the conventional chemical analysis was achieved, with the highest correlation of R2 = 0.8536 for the D vs. the aldehyde concentrations during the thermal oxidation of poly-unsaturated linseed oils, the oil most susceptible to oxidation. A good correlation between the D and aldehyde levels was also achieved for all the other oils. The possibility to simplify and minimize the time of oxidative analysis using the TD NMR sensors D values is discussed as an indicator of the oil’s oxidation quality, as a rapid and accurate methodology for the oil industry.

Surface-Based Post-synthesis Manipulation of Point Defects in Metal Oxides Using Liquid Water.

Initial synthesis of semiconducting oxides leaves behind poorly controlled concentrations of unwanted atomic-scale defects that influence numerous electrical, optical, and reactivity properties. We have discovered through self-diffusion measurements and first-principles computations that poison-free oxide surfaces inject interstitial oxygen atoms into the crystalline solid when simply contacted with liquid water near room temperature. These interstitials diffuse quickly to depths of 20 nm-2 μm and are likely to eliminate prominent classes of unwanted defects or neutralize their action. The mild conditions of operation access a regime for oxide fabrication that relaxes important thermodynamic constraints that hamper defect regulation by conventional methods at higher temperatures. The surface-based approach appears well-suited for use with nanoparticles, porous oxides, and thin films for applications in advanced electronics, renewable energy storage, photocatalysis, and photoelectrochemistry.

NMR Characterization of unfrozen brine vein distribution and structure in model packed beds

When a brine mixed with particles is frozen, some liquid water persists due to the freezing point depression caused by the solute impurity, surface energy, and disjoining pressure (wetting forces). This unfrozen water forms a complex “liquid vein network” (LVN). However, details of the freezing process are still not fully understood, including the permeability/tortuosity of the LVN, and the unfrozen water content at a given temperature. Here, we have applied nuclear magnetic resonance (NMR) relaxation, self-diffusion measurements and magnetic resonance imaging (MRI) to investigate the distribution and structure of LVNs. Magnesium chloride (MgCl2) salt concentrations of 15, 30, and 60 mM were investigated with and without poly-methyl methacrylate (PMMA) particles of diameter 0.4, 9.9, and 102.2 μm, allowing us to quantify unfrozen water content and the structure of the LVN as a function of temperature, MgCl2 concentration, and PMMA particle size. The results of magnetic resonance imaging (MRI) and self-diffusion confirm that the inhibition of ice recrystallization is a function of particle size. To gain information on LVN structure, we compared NMR results to Monte Carlo simulations of freezing in brine-particle systems. Comparisons between laboratory and simulation data suggest that, for our experimental range of temperature (−17.4 °C to −0.9 °C ± 0.5 °C), solutes make the dominant contribution to the unfrozen liquid fraction for particle sizes larger than a few microns, whereas in the finest grained porous media we tested, the unfrozen liquid fraction is controlled primarily by the films that wet particle-ice interfaces.

Minimum miscibility pressure of CO2 and oil evaluated using MRI and NMR measurements

The minimum miscibility pressure (MMP) between CO2 and crude oil is a critical parameter for CO2 enhanced oil recovery (EOR). Whilst different methodologies have been employed to determine MMP, these methods are either time-consuming or unable to be executed in the actual rock core samples from the relevant reservoir and as such, do not directly consider any accompanying kinetic effects. Here we consider a range of nuclear magnetic resonance (NMR) measurement techniques performed on a benchtop NMR apparatus in terms of their ability to estimate MMP; specifically 1D imaging, self-diffusion measurements and T1/T2 relaxation measurements. Such MMP measurements were performed on two model oils (decane and hexadecane), allowing for validation against comparable MMP literature data, and a local crude oil sample – in this case the results were compared against a PVT measurement performed using a high-pressure variable volume cell (VVC). Reasonably good agreement with these alternative sources of MMP data were realized via NMR measurements of self-diffusion; these provided consistent estimates of MMP for a wider range of oils when compared to 1D imaging and NMR relaxation measurements. NMR T2 measurements however performed equivalently to self-diffusion measurements for higher viscosity fluids based on the limited number of samples studied; such measurements require much simpler NMR hardware and are more readily accessible in both the laboratory and in the field.

How to produce confidence intervals instead of confidence tricks: Representative sampling for molecular simulations of fluid self-diffusion under nanoscale confinement.

Ergodicity (or at least the tantalizing promise of it) is a core animating principle of molecular-dynamics (MD) simulations: Put simply, sample for long enough (in time), and you will make representative visits to states of a system all throughout phase space, consistent with the desired statistical ensemble. However, one is not guaranteed a priori that the chosen window of sampling in a production run is sufficiently long to avoid problematically non-ergodic observations; one is also not guaranteed that successive measurements of an observable are statistically independent of each other. In this paper, we investigate several particularly striking and troublesome examples of statistical correlations in MD simulations of nanoconfined fluids, which have profound implications on the quantification of uncertainty for transport phenomena in these systems. In particular, we show that these correlations can lead to confidence intervals on the fluid self-diffusion coefficient that are dramatically overconfident and estimates of this transport quantity that are simply inaccurate. We propose a simple approach-based on the thermally accelerated decorrelation of fluid positions and momenta-that ameliorates these issues and improves our confidence in MD measurements of nanoconfined fluid transport properties. We demonstrate that the formation of faithful confidence intervals for measurements of self-diffusion under nanoscale confinement typically requires at least 20 statistically independent samples, and potentially more depending on the sampling technique used.

Does [Tf2N]- slither? Equivalence of cation and anion self-diffusion activation volumes in 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide.

New high-pressure self-diffusion data are reported for the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide ([EMIM][Tf2N]) at pressures up to 363 MPa in the temperature range 288-348 K. The cation and anion activation volumes derived from these are found to be equal at a fixed temperature, within experimental error, in contradiction to a report in the literature that they differ significantly. Self-diffusion activation volumes derived from our earlier high-pressure diffusion studies also show equality for the respective cations and anions of bis(trifluoromethylsulfonyl)amide, tetrafluoroborate and hexafluorophosphate salts with various cations. Stokes-Einstein-Sutherland analysis and density scaling are applied to the [EMIM][Tf2N] self-diffusion measurements and support the conclusion that pressure effects both cation and anion mass (and hence charge) transport in the same way. The density scaling parameters are consistent with the theoretical predictions of Knudsen et al. and agree with that for the viscosity, as for other ionic liquids.

Stabilizing effects of Ag doping on structure and thermal stability of FeN thin films

In this work, we investigated the effect of Ag doping (2–20 at.%) on the phase formation of iron mononitride (FeN) thin films. Together with deposition of FeN using reactive dc magnetron sputtering, Ag was also co-sputtered at various doping levels between 2–20 at.%. We found that doping of Ag around 5 at.% is optimum to not only improve the thermal stability of FeN but also to reduce intrinsic defects that are invariably present in (even in epitaxial) FeN. Conversion electron Mössbauer spectroscopy and N K-edge x-ray near edge absorption measurements clearly reveal a reduction of defects in Ag doped FeN samples. Moreover, Fe self-diffusion measurements carried out using secondary ion mass spectroscopy depth-profiling and polarized neutron reflectivity in 57Fe enriched samples exhibit an appreciable reduction in Fe self-diffusion in Ag doped FeN samples. Ag being immiscible with Fe and non-reactive with N, occupies grain-boundary positions as nanoparticles and prohibits the fast Fe self-diffusion in FeN.

Suppressing Natural Convection for Self-diffusion Measurement in Liquid Pb Using Shear Cell Technique by Stable Density Layering of Isotopic Concentration

Suppressing Natural Convection for Self-diffusion Measurement in Liquid Pb Using Shear Cell Technique by Stable Density Layering of Isotopic Concentration

Investigation of the aggregation behaviour of the anionic surfactant sodium dodecyl sulfate in ionic liquids 1-allyl-3-methylimidazolium chloride and 1-Ethyl-3-methylimidazolium diethyl phosphate

We investigated the aggregation behaviour of the anionic surfactant sodium dodecyl sulfate (SDS) in 1-allyl-3-methylimidazolium chloride (AMIMCl) ionic liquid at three temperatures 323 K, 333 K and 343 K using 1H Nuclear Magnetic Resonance (NMR) chemical shift and Pulsed-Field Gradient (PFG) spin-echo NMR self-diffusion measurements. Chemical shifts of SDS protons and diffusion coefficients of SDS as a function of the surfactant concentration have breakpoints, which indicate an onset of the surfactant micellisation. We estimated the critical micelle concentration (cmc) with high accuracy from SDS methyl protons' chemical shifts and the micelles' average aggregation number from diffusion coefficients. The formation of micelles does not influence the diffusion and chemical shifts of AMIMCl.We determined water concentration in the samples from the NMR spectra. We did not find evidence that water affects the aggregation process since water content practically does not influence the SDS protons' chemical shifts and diffusion coefficients. However, water appears to influence the diffusion and chemical shifts of AMIMCl.We also investigated the behaviour of SDS in 1-Ethyl-3-methylimidazolium diethyl phosphate (EMIMDEP) hydrophilic ionic liquid. The value of the Gordon parameter of EMIMDEP indicates that it does not possess the ability to support the self-assembly of amphiphiles. Within this work, we treat the system SDS/EMIMDEP as a reference one.SDS forms a lamellar phase in AMIMCl at high concentration, as revealed by Small Angle X-ray Scattering (SAXS) and Polarised Optical Microscopy (POM) investigations. At about 358 K, a transition from the lamellar phase to the isotropic liquid phase occurs. No other liquid-crystalline phase in this system was determined.

Ionic (Proton) transport and molecular interaction of ionic Liquid–PBI blends for the use as electrolyte membranes

Protic ionic liquids (PILs) are discussed as new candidates for the use as non-aqueous electrolytes for fuel cells operating at temperatures above 80 °C. The molecular interactions in Diethylmethylammonium triflate ([Dema][TfO]) doped polybenzimidazole (PBI) blend membranes and the proton transport mechanism were investigated by means of TGA, IR and NMR. The mobility of the PIL ions is restricted to the PBI host polymer. The [Dema]+ cations and [TfO]− anions interact strongly via H bonds with the polar groups of the PBI chains. This will significantly confine the proton conductivity of the membrane to vehicular transport. The proton transport was investigated by comparing to an analogous liquid state model using the monomer benzimidazole (BIm) instead of the PBI polymer. During fuel cell operation, it is unavoidable that residual water is present in significant quantities. Resulting from 1H NMR and PFG self-diffusion measurements, proton transport in the liquid state model takes place via a cooperative mechanism involving all of the species NH[Dema]+/NHBIm/H2O depending on the water fraction. Thus, it is suggested that conductivity in the PIL–PBI membrane be mainly provided by the cooperative transport of the protons. This study is intended to broaden understanding of the structure and proton transport mechanism, as well as to give possible ways to optimize PIL electrolyte doped polymer blend membranes for intermediate operating temperatures.

Time-of-flight modulated intensity small-angle neutron scattering measurement of the self-diffusion constant of water

The modulated intensity by zero effort small-angle neutron scattering (MI-SANS) technique is used to measure scattering with a high energy resolution on samples normally ill-suited for neutron resonance spin echo. The self-diffusion constant of water is measured over a q–t range of 0.01–0.2 Å−1 and 70–500 ps. In addition to demonstrating the methodology of using time-of-flight MI-SANS instruments to observe diffusion in liquids, the results support previous measurements on water performed with different methods. This polarized neutron technique simultaneously measures the intermediate scattering function for a wide range of time and length scales. Two radio frequency flippers were used in a spin-echo setup with a 100 kHz frequency difference in order to create a high-resolution time measurement. The results are compared with self-diffusion measurements made by other techniques and the general applicability of MI-SANS at a pulsed source is assessed.