Molecular Diffusion Coefficient Research Articles

Sugar-influenced water diffusion, interaction, and retention in clay interlayer nanopores probed by theoretical simulations and experimental spectroscopies

Understanding the hydrodynamics in clay nanopores is important for gaining insights into the trapping of water, nutrients, and contaminants in natural and engineered soils. Previous investigations have focused on the interlayer organization and molecular diffusion coefficients (D) of cations and water molecules in cation-saturated interlayer nanopores of smectite clays. Little is known, however, about how these interlayer dynamic properties are influenced by the ubiquitous presence of small organic compounds such as sugars in the soil environment. Here we probed the effects of glucose molecules on montmorillonite interlayer properties. Molecular dynamics simulations revealed re-structuring of the interlayer organization of the adsorptive species. Water-water interactions were disrupted by glucose-water H-bonding interactions. “Dehydration” of the glucose-populated nanopore led to depletion in the Na solvation shell, which resulted in the accumulation of both Na ions (as inner-sphere complexes) and remaining hydrated water molecules at the mineral surface. This accumulation led to a decrease in both DNa and Dwater. In addition, the reduction in Dglucose as a function of increasing glucose content can be explained by the aggregation of glucose molecules into organic clusters H-bonded to the mineral surface on both walls of the nanopore. Experimental nuclear magnetic resonance and X-ray diffraction data were consistent with the theoretical predictions. Compared to clay interlayers devoid of glucose, increased intensities and new peaks in the 23Na nuclear magnetic resonance spectra confirmed increasing immobilization of Na as a function of increasing glucose content. And, the X-ray diffraction data indicated a reduced collapse of glucose-populated interlayers exposed to decreasing moisture conditions, which led to the maintenance of hydrated clay nanopores. The coupling of theoretical and experimental findings sheds light on the molecular to nanoscale mechanisms that control the enhanced trapping of water molecules and solutes within sugar-enriched clay nanopores.

Ultrahigh b-values MRI in normal human prostate: Initial research on reproducibility and age-related differences.

To investigate the reproducibility of diffusion-weighted imaging (DWI) with ultrahigh b-values, and analyze the age-related differences in normal prostates. In all, 67 healthy participants were divided into three age groups (group A, 15-30 years; group B, 31-50 years; group C, ≥51 years), and underwent DWI scanning twice with 15 b-factors from 0 to 3000 at 3.0T. Triexponential fits were applied to calculate the molecular diffusion coefficient (D), the pseudo-diffusion coefficient (D*), the ultrahigh apparent diffusion coefficient (ADCuh ), and perfusion fraction (f). The interobserver and short-term interscan reproducibility were evaluated, and the change in these parameters with age were assessed. The D, ADCuh , and f values presented good to excellent reproducibility. With increasing age, a trend of increasing D values was observed, with significant difference in both peripheral zone (PZ, P = 0.01) and central gland (CG, P = 0.01) of normal prostate tissue. The f value increased in the CG beginning at 50 years of age while the ADCuh value decreased in the PZ after 50 years of age; all of them showed significant differences between groups A and C and groups B and C (P = 0.01/0.01). The D, ADCuh , and f values have good to excellent reproducibility in the normal prostate, and these values change with age. The ultrahigh b-values magnetic resonance imaging (MRI) can provide additional information (ADCuh ), which is different from the IVIM (intravoxel incoherent motion)-derived parameters. 1 Technical Efficacy: Stage 2 J. MAGN. RESON. IMAGING 2017;46:801-812.

Lymph node metastasis in head and neck squamous carcinoma: Efficacy of intravoxel incoherent motion magnetic resonance imaging for the differential diagnosis

PurposeTo evaluate the value of pure molecular diffusion(D), perfusion-related diffusion (D*), perfusion fraction (f) and apparent diffusion coefficient (ADC) based on intravoxel incoherent motion (IVIM) theory for differential diagnosis of metastatic lymph nodes (LNs) in head and neck squamous cell carcinoma(HNSCC). Materials and methods29 patients with HNSCC and 20 patients with lymph node hyperplasia (LNH) were enrolled in this retrospective study, underwent magnetic resonance (MR) examination. IVIM Diffusion-weighted imaging (IVIM-DWI) was performed with 13 b values. D, D*, f and ADC values were compared between two groups. The diagnostic value of ADC, D, D* and D·D* value were evaluated by Receiver operating characteristic (ROC) curve. Two radiologists measured D, D*, f and ADC values independently. Results33 malignant LNs in HNSCC group and 22 benign LNs in LNH group (minimum diameter, ≥5mm) were successfully examined, ADC(P<0.05), D (P<0.01) and f (P<0.01) were significantly lower in malignant LNs than that in benign LNs, whereas D* was significantly higher (P<0.01). The area under the ROC curve (AUC) for D·D* was 0.983 and was larger than that for D* (0.952), D (0.78) and ADC (0.67). ConclusionOur results indicate that IVIM DWI is feasible in the diagnosis of LN metastasis. D was significantly decreased in malignant LNs reflected increased nuclear-to-cytoplasmic ratio tissue, and D* was significantly increased reflected increased blood vessel generation and parenchymal perfusion in malignant LNs.

Soret coefficient of the n-dodecane-n-hexane binary mixture under high pressure.

In the present work, the Soret coefficient has been determined at high pressure for a binary hydrocarbon mixture by combining the thermogravitational column and the dynamic near-field imaging techniques. The analyzed mixture is an iso-massic n -dodecane-n -hexane mixture at 298.15K. The molecular diffusion coefficient has been measured up to 20MPa by means of the dynamic analysis of the light scattered by non-equilibrium concentration fluctuations. With a cylindrical thermogravitational column the thermodiffusion coefficient was determined from 0.1MPa to 10MPa. Density, as well as, mass expansion and thermal expansion have been measured with a high pressure densimeter. Dynamic viscosity at up to 20MPa has been determined with a high pressure viscometer. This work shows the decreasing tendency of both the molecular diffusion and the thermodiffusion coefficient with increasing pressure.

Intravoxel incoherent motion diffusion-weighted imaging of bone marrow in patients with acute myeloid leukemia: a pilot study of prognostic value.

To investigate the value of intravoxel incoherent motion (IVIM) parameters in evaluation of prognosis in patients with acute myeloid leukemia (AML) before treatment. Fifty-three patients before standard chemotherapy underwent MRI scans at 1.5 Tesla using conventional diffusion weighted imaging (DWI) and IVIM (b = 0, 10, 25, 50, 100, 200, 400, 600, 800, 1000, 1200 s/mm2 ) in the sagittal plane covering the lumbar bone marrow. The IVIM parameters (perfusion fraction [f], molecular diffusion coefficient [D], and perfusion-related D [D*] and apparent diffusion coefficient (ADC) were extracted from the bone marrow images. All patients were divided into complete remission (CR) and nonremission (NR) group according to the treatment response. All patients underwent the first remission induction chemotherapy, with 33 patients achieved CR and 20 patients achieved NR. The ADC values were not significant different between the two groups (P = 0.118). However, D value of CR group was significantly higher (P = 0.010), and f value of CR group was significantly lower (P = 0.021) than those of NR group. D* values had no significant differences between the two groups (P = 0.955). The D and f values were significant prognostic factors of AML after controlling for potential confounding factors (age, gender and smoking). Using receiver operator characteristic analysis, the area under the curve of D and f were 0.759 and 0.666, respectively, in evaluating prognosis of AML before treatment. There were significant differences in IVIM parameters between CR and NR patients of AML before treatment, and the D and f could play a potential role in prognosticating patients with AML. 1 Technical Efficacy: Stage 2 J. MAGN. RESON. IMAGING 2017;46:476-482.

Molecular Diffusion in Plasma Membranes of Primary Lymphocytes Measured by Fluorescence Correlation Spectroscopy.

Fluorescence correlation spectroscopy (FCS) is a powerful technique for studying the diffusion of molecules within biological membranes with high spatial and temporal resolution. FCS can quantify the molecular concentration and diffusion coefficient of fluorescently labeled molecules in the cell membrane. This technique has the ability to explore the molecular diffusion characteristics of molecules in the plasma membrane of immune cells in steady state (i.e., without processes affecting the result during the actual measurement time). FCS is suitable for studying the diffusion of proteins that are expressed at levels typical for most endogenous proteins. Here, a straightforward and robust method to determine the diffusion rate of cell membrane proteins on primary lymphocytes is demonstrated. An effective way to perform measurements on antibody-stained live cells and commonly occurring observations after acquisition are described. The recent advancements in the development of photo-stable fluorescent dyes can be utilized by conjugating the antibodies of interest to appropriate dyes that do not bleach extensively during the measurements. Additionally, this allows for the detection of slowly diffusing entities, which is a common feature of proteins expressed in cell membranes. The analysis procedure to extract molecular concentration and diffusion parameters from the generated autocorrelation curves is highlighted. In summary, a basic protocol for FCS measurements is provided; it can be followed by immunologists with an understanding of confocal microscopy but with no other previous experience of techniques for measuring dynamic parameters, such as molecular diffusion rates.

Modeling of Pressure Dependence of Interfacial Tension Behaviors of Supercritical CO2 + Crude Oil Systems Using a Basic Parachor Expression

Parachor based expressions (basic and mechanistic) are often used to model the experimentally observed pressure dependence of interfacial tension (IFT) behaviors of complex supercritical carbon dioxide (sc-CO2) and crude oil mixtures at elevated temperatures. However, such modeling requires various input data (e.g. compositions and densities of the equilibrium liquid and vapor phases, and molecular weights and diffusion coefficients for various components present in the system). In the absence of measured data, often phase behavior packages are used for obtaining these input data for performing calculations. Very few researchers have used experimentally measured input data for performing parachor based modeling of the experimental IFT behaviors of sc-CO2 and crude oil systems that are of particular interest to CO2 injection in porous media based enhanced oil recovery (EOR) operations.This study presents the results of parachor based modeling performed to predict pressure dependence of IFT behaviors of a complex sc-CO2 and crude oil system for which experimentally measured data is available in public domain. Though parachor model based on calculated IFT behaviors shows significant deviation from the measured behaviors in high IFT region, difference between the calculated and the experimental behaviors appears to vanish in low IFT region. These observations suggest that basic parachor expression based calculated IFT behaviors in low IFT region follow the experimental IFT behaviors more closely.An analysis of published studies (basic and mechanistic parachor expressions based on modeling of pressure dependence of IFT behaviors of both standard and complex sc-CO2 and crude oil systems) and the results of this study reinforce the need of better description of gas-oil interactions for robust modeling of pressure dependence of IFT behavior of these complex systems.

In Vitro Binding of 6S RNA Mango to RNA Polymerase by Two Photon Fluorescence Cross Correlation Spectroscopy

The assembly of RNA and protein complexes is a fundamental process for life but has been difficult to study both in vitro and in vivo. Recently a novel aptamer based method to fluorescently label RNA molecules has been reported(Dolgosheina et al. 2014). Here we report the successful utilization of the RNA Mango + thiazole orange derivative to measure the in vitro binding of 6S RNA to RNA Polymerase from E. coli. By two photon Fluorescence Cross Correlation Spectroscopy, we are able to independently measure the molecular brightness, diffusion coefficient and concentration of 6S RNA Mango, RNA Polymerase GFP and complex as we increase RNA Polymerase concentration giving us an estimate for the equilibrium binding constant of the complex in vitro. This experiment demonstrates the utility of RNA Mango for both in vitro and in vivo single molecule experiments.Dolgosheina, Elena V., Sunny C. Y. Jeng, Shanker Shyam S. Panchapakesan, Razvan Cojocaru, Patrick S. K. Chen, Peter D. Wilson, Nancy Hawkins, Paul A. Wiggins, and Peter J. Unrau. 2014. “RNA Mango Aptamer-Fluorophore: A Bright, High-Affinity Complex for RNA Labeling and Tracking.” ACS Chemical Biology 9 (10): 2412-20.

An Ensemble Modeling Approach for Estimating Diffusive Tortuosity for Saturated Soils From Porosity

Apparent diffusion constants in soil are generally estimated by dividing molecular diffusion coefficient for a solute with soil tortuosity (τ) values. Several models have been proposed to estimate τ from soil porosity (ϕ) alone, but most of these models fail when the variability in observed τ-ϕ pairs increases. Pedotransfer functions can be used to predict τ from easy-to-measure soil properties such soil texture, organic carbon contents, and ϕ, but such an approach requires more measurements to be performed than just measuring ϕ. Here, we show that τ may be estimated from ϕ alone using the ensemble averaging approach. We examined seven different analytical expressions for τ-ϕ and seven different ensemble-modeling approaches to estimate τ for 100 pairs of τ-ϕ collected from a wide geographical area. Modeling results showed that the Bayesian model averaging method was the best ensemble-modeling approach for estimating τ from ϕ. Of 119 different combinations of τ (ϕ) models, three models derived considering (1) packing of square-shaped particles, (2) fractal geometry with particles of different sizes, and (3) percolation theory were identified as the best individual models for ensemble modeling. The coefficient of determination (0.67), root-mean-squared error (0.23), and the Akaike information criterion (94.37) values for this ensemble model were better than those when a single model was used for prediction. Inclusion of these three models that are based on both fractal and regular geometrical shapes for particles of different sizes may be a reason for improved performance of the ensemble approach. These results suggest that τ may be estimated from ϕ using the ensemble approach without the need for additional soil data, as is done in a pedotransfer function approach.

Intravoxel Incoherent Motion (IVIM)Diffusion Weighted Imaging (DWI) in the Periferic Prostate Cancer Detection and Stratification.

The aim of this study was to compare theIntravoxel Incoherent Motion (IVIM) parameters between healthy Peripheral Zone (PZ), Benign Prostatic Hyperplasia (BPH) and Prostate Cancer (PCa) and compare them to assess whether there was correlation with Gleason Score (GS) grading system. Thirty-one patients with suspect of PCa underwent 1.5T Multi-Parametric Magnetic Resonance Imaging (MP-MRI) with endorectal coil with a protocol including T2WI, DWI using 10 b values (0, 10, 20, 30, 50, 80, 100, 200, 400, 1000s/mm2) and DCE. Monoexponential and IVIM model fits were used to calculate both apparent diffusion coefficient (ADC) and the following IVIM parameters: molecular diffusion coefficient (D), perfusion-related diffusion coefficient (D*) and perfusion fraction (f). The ADC and D values were significantly lower in the PCa (0.70±0.16×10-3mm2/s and 0.88±0.31×10-3mm2/s) compared to those found in the PZ (1.22±0.20×10-3mm2/s and 1.78±0.34×10-3mm2/s) and in the BPH (1.53±0.23×10-3mm2/s and 1.11±0.28×10-3mm2/s). The D* parameter was significantly increased in the PCa (5.35±5.12×10-3mm2/s) compare to the healthy PZ (3.02±2.86×10-3mm2/s), instead there was not significantly difference in the PCa compare to the BPH (5.61±6.77×10-3mm2/s). The f was statistically lower in the PCa (9.01±5.20%) compared to PZ (10.57±9.30%), but not significantly different between PCa and BPH (9.29±7.29%). The specificity, sensitivity and accuracy of T2WI associated with DWI and IVIM were higher (100, 98 and 99%, respectively) than for T2WI/DWI and IVIM alone (89, 92 and 90%, respectively). Only for ADC was found a statistical difference between low- and intermediate-/high-grade tumors. Adding IVIM to the MP-MRI could increase the diagnostic performance to detect clinically relevant PCa. ADC values have been found to have a rule to discriminate PCa reliably from normal areas and differed significantly in low- and intermediate-/high-grade PCa. In contrast, IVIM parameters were unable to distinguish between the different GS.

Evaluating Diffusivity of Toluene in Heavy Oil Using Nuclear Magnetic Resonance Imaging

Solvent-based processes have shown technical advantages over thermal techniques for recovery of heavy oil and bitumen. The success of these processes relies on accurate computation of molecular diffusion coefficient which determines how fast a solvent penetrates into oil. Concentration profile measurements of solvent in oil are used for the determination of the molecular diffusion coefficient. Although numerous experimental techniques have been proposed, the accurate estimation of this parameter is still a topic of debate in the literature. In this work, 1-D nuclear magnetic resonance imaging (MRI) is employed to obtain diffusivity data for a toluene–heavy oil system. Diffusion of toluene in heavy oil was monitored for 20 days at a controlled temperature of 35 °C and ambient pressure. Over time, toluene diffusion into oil leads to changes in spatial distribution of T1 and T2 that affect the received signal. This serves as the basis of the solvent and heavy oil concentration estimation. Consequently, conce...

Prediction of the moments in advection-diffusion lattice Boltzmann method. II. Attenuation of the boundary layers via double-Λ bounce-back flux scheme.

Impact of the unphysical tangential advective-diffusion constraint of the bounce-back (BB) reflection on the impermeable solid surface is examined for the first four moments of concentration. Despite the number of recent improvements for the Neumann condition in the lattice Boltzmann method-advection-diffusion equation, the BB rule remains the only known local mass-conserving no-flux condition suitable for staircase porous geometry. We examine the closure relation of the BB rule in straight channel and cylindrical capillary analytically, and show that it excites the Knudsen-type boundary layers in the nonequilibrium solution for full-weight equilibrium stencil. Although the d2Q5 and d3Q7 coordinate schemes are sufficient for the modeling of isotropic diffusion, the full-weight stencils are appealing for their advanced stability, isotropy, anisotropy and anti-numerical-diffusion ability. The boundary layers are not covered by the Chapman-Enskog expansion around the expected equilibrium, but they accommodate the Chapman-Enskog expansion in the bulk with the closure relation of the bounce-back rule. We show that the induced boundary layers introduce first-order errors in two primary transport properties, namely, mean velocity (first moment) and molecular diffusion coefficient (second moment). As a side effect, the Taylor-dispersion coefficient (second moment), skewness (third moment), and kurtosis (fourth moment) deviate from their physical values and predictions of the fourth-order Chapman-Enskog analysis, even though the kurtosis error in pure diffusion does not depend on grid resolution. In two- and three-dimensional grid-aligned channels and open-tubular conduits, the errors of velocity and diffusion are proportional to the diagonal weight values of the corresponding equilibrium terms. The d2Q5 and d3Q7 schemes do not suffer from this deficiency in grid-aligned geometries but they cannot avoid it if the boundaries are not parallel to the coordinate lines. In order to vanish or attenuate the disparity of the modeled transport coefficients with the equilibrium weights without any modification of the BB rule, we propose to use the two-relaxation-times collision operator with free-tunable product of two eigenfunctions Λ. Two different values Λ_{v} and Λ_{b} are assigned for bulk and boundary nodes, respectively. The rationale behind this is that Λ_{v} is adjustable for stability, accuracy, or other purposes, while the corresponding Λ_{b}(Λ_{v}) controls the primary accommodation effects. Two distinguished but similar functional relations Λ_{b}(Λ_{v}) are constructed analytically: they preserve advection velocity in parabolic profile, exactly in the two-dimensional channel and very accurately in a three-dimensional cylindrical capillary. For any velocity-weight stencil, the (local) double-Λ BB scheme produces quasi-identical solutions with the (nonlocal) specular-forward reflection for first four moments in a channel. In a capillary, this strategy allows for the accurate modeling of the Taylor-dispersion and non-Gaussian effects. As illustrative example, it is shown that in the flow around a circular obstacle, the double-Λ scheme may also vanish the dependency of mean velocity on the velocity weight; the required value for Λ_{b}(Λ_{v}) can be identified in a few bisection iterations in given geometry. A positive solution for Λ_{b}(Λ_{v}) may not exist in pure diffusion, but a sufficiently small value of Λ_{b} significantly reduces the disparity in diffusion coefficient with the mass weight in ducts and in the presence of rectangular obstacles. Although Λ_{b} also controls the effective position of straight or curved boundaries, the double-Λ scheme deals with the lower-order effects. Its idea and construction may help understanding and amelioration of the anomalous, zero- and first-order behavior of the macroscopic solution in the presence of the bulk and boundary or interface discontinuities, commonly found in multiphase flow and heterogeneous transport.

Methods for Measuring Molecular Diffusion Coefficients of Large Proteins and Bio-nanopartilces

拡散係数（分子拡散係数あるいは相互拡散係数）Dmは，クロマトグラフィーや乾燥などさまざまな分離操作・装置の設計に必要な重要な物性値である．また，物質の大きさを知るための重要な情報でもある．拡散係数の測定のために，さまざまな方法が開発され使用されているが，とくに分子量の大きいタンパク質やDNA，さらにはバイオナノ粒子のDmは，ほとんど報告されていない．本研究では，タンパク質および修飾タンパク質（PEG化タンパク質）のDmを比較的簡単な測定操作と装置が簡便である細管内層流速度分布を利用したTaylor法と動的光散乱法で測定した．どちらの方法でもほぼ同じDm値を得ることができた．ただし，それぞれの方法には特徴と問題点があるので，よく理解して相補的な方法として使用することが望ましい．

Quasi-isobaric ignition near the flammability limits. Flame balls and self-extinguishing flames

Asymptotic analyses are presented for spherical flame kernels (steady solutions) and slow flame expansion in mixtures near and beyond the flammability limits corresponding to a molecular diffusion coefficient of the limiting species greater than the thermal diffusivity, Lewis number smaller than unity, Le < 1. The results concern also the dynamical quenching observed in micro-gravity experiments (self-extinguishing flames) at large radius of flame expanding in non-flammable mixtures (beyond the flammability limits of planar flames).

13C and 1H NMR measurements to investigate the kinetics and the mechanism of acetic acid (CH3CO2H) ionization as a model for organic acid dissociation dynamics for polymeric membrane water filtration

Abstract The formation of ionic charge carriers and their transport in acetic acid (CH3COOH): water mixtures have been investigated by 13C and 1H NMR. The obtained dissociation constant from the NMR measurements is close to pKa = 4.70 in a highly diluted system which is in full agreement with literature values. The maximum molar concentration of ions (H3O+ and CH3COO−) is found at a water mole fraction around 0.5 to 0.6. Remarkably, minima in the molecular diffusion coefficients and ionic mobility are observed at this concentration. Ionic concentrations, ionic strength and the pH curve were obtained for any water content based on the 13C and 1H NMR as well as pH measurements and the numerical calculations. The data is relevant for the understanding and optimization of the properties of polymeric nanofiltration membranes for organic ion removal. They provide interesting insight into the water dependence of the viscoelastic and kinematic properties, the charge formation mechanism and the dissociation limit, especially for highly diluted systems simulating the case of ionic pollutants.

Relevance and Assessment of Molecular Diffusion Coefficients in Liquid Chromatography

Molecular diffusion plays an important role in high-performance liquid chromatography, especially in fundamental column performance studies. An accurate knowledge of the molecular diffusion coefficients (D m) of compounds selected for column evaluation is therefore crucial. In this review, a general overview is presented of the advantages and drawbacks of correlation-based and experimental methods that can be employed to determine molecular diffusion coefficients. The former include the Wilke–Chang, Scheibel, Reddy–Doraiswamy, Lusis–Ratcliff and Hayduk–Laudie equations, and other empirical correlations based on the Wilke–Chang equation. It is discussed how the association factor (ψ) that is required in several of these correlations can be obtained from the solubility parameter (δ). Frequently used experimental methods include the light scattering, nuclear magnetic resonance, peak parking and Taylor–Aris method, and methods employing microfluidic devices. The principles of these experimental methods are elucidated in detail. Moreover, the influence of several parameters, such as solute characteristics, solvent viscosity, temperature and pressure on the molecular diffusion coefficient is described.

Label-Free Measurements of Tenofovir Diffusion Coefficients in a Microbicide Gel Using Raman Spectroscopy

Confocal Raman spectroscopy was implemented in a new label-free technique to quantify molecular diffusion coefficients within gels. A leading anti-HIV drug, tenofovir, was analyzed in a clinical microbicide gel. The gel was tested undiluted, and in 10%-50% wt/wt dilutions with vaginal fluid simulant to capture the range of conditions likely occurring in vivo. The concentration distributions of tenofovir in gel over time and space were measured and input to a mathematical diffusion model to deduce diffusion coefficients. These were 3.16 ± 0.11 × 10−6 cm2/s in undiluted gel, and increased by 11%-46% depending on the extent of dilution. Results were interpreted with respect to traditional release rate measurements in devices such as Franz cells. This comparison highlighted an advantage of our assay in that it characterizes the diffusive barrier within the gel material itself; in contrast, release rate in the traditional assay is affected by external conditions, such as drug partitioning at the gel/liquid sink interface. This new assay is relevant to diffusion in polymeric hydrogels over pharmacologically relevant length scales, for example, those characteristic of topical drug delivery. Resulting transport parameters are salient measures of drug delivery potential, and serve as inputs to computational models of drug delivery performance.

Thermodiffusion, molecular diffusion and Soret coefficients of aromatic+n-alkane binary mixtures.

In the present work, we have measured the thermodiffusion coefficient of 51 binary liquid mixtures at 25 oC. These mixtures correspond to the series of the aromatics toluene and 1-methylnaphthalene with n-alkanes nCi (i = 6, 8, 10, 12, and 14) at different mass fractions in the whole range. For that, we have used the thermogravitational technique. It is shown that the thermodiffusion coefficient is a linear function of the mass fraction in all the mixtures. Extrapolating the lines, we obtain the thermodiffusion coefficient in dilute solutions of n-alkanes for both toluene and 1-methylnaphthalene. These limiting values show a linear dependence with the inverse of the product of the molecular weights. In addition, we have measured the molecular diffusion coefficient of all the mixtures at 0.5 of mass fraction and at 25 oC, by the sliding symmetric tubes technique. It is observed that the product of this coefficient with the viscosity at the same concentrations takes a constant value for each of the series considered. Finally, we have also determined the Soret coefficient of the equimass mixtures by the combination of the measurements of thermodiffusion and molecular diffusion coefficients.

Three-dimensional analysis of spreading and mixing of miscible compound in heterogeneous variable-aperture fracture

As mass transport mechanisms, the spreading and mixing (dilution) processes of miscible contaminated compounds are fundamental to understanding reactive transport behaviors and transverse dispersion. In this study, the spreading and dilution processes of a miscible contaminated compound in a three-dimensional self-affine rough fracture were simulated with the coupled lattice Boltzmann method (LBM). Moment analysis and the Shannon entropy (dilution index) were employed to analyze the spreading and mixing processes, respectively. The corresponding results showed that the spreading process was anisotropic due to the heterogeneous aperture distribution. A compound was transported faster in a large aperture region than in a small aperture region due to the occurrence of preferential flow. Both the spreading and mixing processes were highly dependent on the fluid flow velocity and molecular diffusion. The calculated results of the dilution index showed that increasing the fluid flow velocity and molecular diffusion coefficient led to a higher increasing rate of the dilution index.

Adsorption of pyridine from aqueous solutions by polymeric adsorbents MN 200 and MN 500. Part 2: Kinetics and diffusion analysis

The adsorption kinetics of pyridine adsorption on Macronet adsorbents MN 200 and MN 500 from aqueous solution was investigated at various initial pyridine concentrations and temperatures. The Weber-Morris plots revealed the influence of both external film diffusion and intraparticle diffusion resistances. The two linear regions in Weber-Morris plots were attributed to macropore and micropore diffusion, respectively, which was associated to the bimodal pore size distribution of the adsorbents. New insights into the diffusion mechanisms were highlighted, with the proposed internal film diffusion resistance dominating into the macropore region, whereas homogeneous particle diffusion resistance describes diffusion in the micropore region. The importance of pore and surface diffusion in the micropores was noted in contributing to the observed diffusion kinetics. The pore diffusion coefficient was estimated from PFG (pulsed-field gradient) parameter and molecular diffusion coefficient of pyridine in bulk liquid. A greater contribution of the surface diffusion to the overall diffusion kinetics was found for MN 500 as inferred from a proposed calculation method, which agrees with its better adsorption performance. The overall findings highlight the effect of pore structure onto the diffusion mechanisms inside the pores and help to gain a better understanding into the adsorption kinetics of these Macronet adsorbents which are promising materials for the removal of N-heterocyclic compounds from waste water.