Determination Of Diffusion Coefficients Research Articles

Measuring of translational and rotational local temperatures of a single gold nanocrescent in glycerol

The gold nanocrescent (NC) particles possess a strong plasmon resonance which gives them a strong scattering cross section. They can thus be easily tracked using dark-field microscopy. In this study, we improved the optical configuration setup of dark-field video microscope to simultaneously measure the translational and rotational local temperatures within a glycerol medium. The translational and rotational local temperatures have been measured on the same single gold nanocrescent particle when it was excited by green and red laser. The rotational local temperature was measured by the technique of rotational scattering correlation spectroscopy (RSCS) and the translational local temperature was measured by tracking a single nanoparticle technique through the determination of translational diffusion coefficient under Brownian motion. The result showed that the translational local temperature was significant lower than the rotational local temperature for the same single gold nanocrescent. Remarkablely, we can affirm that the heterogeneity of the optical environment leads to the difference between these two temperatures. The obtained results have a great potential to probe the local nanorheology of a material.

Isotope effects on the high pressure viscosity of liquid water measured by differential dynamic microscopy

Differential dynamic microscopy is performed in diamond anvil cells to measure the viscosity of water along the 24 °C isotherm to high pressure by the determination of the tracer diffusion coefficient of monodisperse silica spheres of known diameter and the application of the Stokes–Einstein–Sutherland equation. This technique allows liquid samples to be compressed to greater pressure prior to freezing than with other viscometry methods. The highest-pressure measurement was made at 1.67 GPa, considerably deeper into the supercompressed regime than previously reported. The effect of the isotopic composition is investigated with samples of normal water, heavy water, and partially deuterated water. When data below 0.25 GPa are excluded, a free volume model fits the observed viscosities well, yielding a theoretical glass transition density close to that observed in very-high-density amorphous ice. The improved fit above 0.25 GPa coincides with the loss of other anomalous behaviors in liquid water caused by hydrogen bonding and represents a transition to properties closer to those of a simple liquid.

Reduced Artifact Approach for Determining Diffusion Coefficients in Time-Resolved Microscopy

Ultrafast microscopy methods traditionally assume a Gaussian profile to extract excited state diffusivities from transport measurements. Although this fitting method recovers accurate diffusion coe...

Diffusion process in photoreaction of ketoprofen probed by transient grating method

Translational diffusion dynamics in photoreaction of ketoprofen (KP), one of the most popular nonsteroidal anti−inflammatory drugs, with and without triethylamine (TEA) in methanol was studied by transient grating method coupled with transient absorption spectroscopy. We successfully determined diffusion coefficients of neutral, carboxylate anion, ketyl radical of KP as well as ketyl biradical complex with TEA in methanol for the first time. The diffusion coefficients for the ketyl radical (6.9 × 10−10 m2 s−1), the carboxylate anion (8.1 × 10−10 m2 s−1), and the complex (5.6 × 10−10 m2 s−1) were found to be smaller than that for neutral KP (9.8 × 10−10 m2 s−1). The molecular volume, the viscosity of the solvent, and/or a specific attractive interaction with solvent molecules would contribute to the diffusion process of these species. These new findings on the diffusion property and the interaction of each species with surrounding molecules are essential for understanding the photoreaction of KP with various biomolecules in vivo.

Drying kinetic measurements of polymer nanolayers – Experimental results with a model-based validation and interpretation of solvent diffusion

This contribution presents a method to examine the drying process of thin films of polymer gravimetrically, ranging from a few micrometers to below 20nm using a quartz crystal microbalance (QCM). Polyvinyl acetate (PVAc) and toluene (tol) serve as the model system to validate the method by drying experiments, simulations and the determination of the concentration dependent solvent diffusion coefficient. The results show that even on the nanometer scale, the diffusion coefficient is not a function of film thickness, which is contrary to the observations that can be found in literature. A thin polymer film, still loaded with residual solvent, is placed into a flow channel with controlled drying conditions. The QCM gravimetrically measures the drying curve and precisely detects changes of mass fractions on the scale of a hundredth of a percent over the course of hours, which translates to changes in layer thickness as small as to 0.1nm per hour. The presented method is a general-purpose tool for measuring concentration-dependent diffusion coefficients, which is relevant to all sorts of thicknesses and coatings. Since nanolayers are employed, in a reasonable amount of time diffusion coefficients in the order of 10−18m2s−1 are accessible.

Predictive Value of Early Post-Treatment Diffusion-Weighted MRI for Recurrence or Tumor Progression of Head and Neck Squamous Cell Carcinoma Treated with Chemo-Radiotherapy

Aims: To investigate the predictive capacity of early post-treatment diffusion-weighted magnetic resonance imaging (MRI) for recurrence or tumor progression in patients with no tumor residue after chemo-radiotherapy (CRT) for head and neck squamous cell carcinoma, and, to assess the predictive capacity of pre-treatment diffusion-weighted MRI for persistent tumor residue post-CRT. Materials and Method: A single center cohort study was performed in one French hospital. All patients with squamous cell carcinoma receiving CRT (no surgical indication) were included. Two diffusion-weighted MRI were performed: one within 8 days before CRT and one 3 months after completing CRT with determination of median tumor apparent diffusion coefficient (ADC). Main outcome: The primary endpoint was progression-free survival. Results: 59 patients were included prior to CRT and 46 (78.0%) completed CRT. A post-CRT tumor residue was found in 19/46 (41.3%) patients. In univariate analysis, initial ADC was significantly lower in patients with residue post CRT (0.56 ± 0.11 versus 0.79 ± 0.13; p < 0.001). When initial ADC was dichotomized at the median, initial ADC lower than 0.7 was significantly more frequent in patients with residue post CRT (73.7% versus 11.1%, p < 0.0001). In multivariate analysis, only initial ADC lower than 0.7 was significantly associated with tumor residue (OR = 22.6; IC [4.9–103.6], p < 0.0001). Among 26 patients without tumor residue after CRT and followed up until 12 months, 6 (23.1%) presented recurrence or progression. Only univariate analysis was performed due to a small number of events. The only factor significantly associated with disease progression or early recurrence was the delta ADC (p = 0.0009). When ADC variation was dichotomized at the median, patients with ADC variation greater than 0.7 had time of disease-free survival significantly longer than patients with ADC variation lower than 0.7 (377.5 [286–402] days versus 253 [198–370], p < 0.0001). Conclusion and relevance: Diffusion-weighted MRI could be a technique that enables differentiation of patients with high potential for early recurrence for whom intensive post-CRT monitoring is mandatory. Prospective studies with more inclusions would be necessary to validate our results.

A numerical model of an immiscible surfactant drop spreading over thin liquid layers using CFD/VOF approach

Numerical investigations of immiscible surfactant drops spreading over thin liquid substrates have been carried out. The CFD numerical model is based on a volume of fluid technique (VOF) coupled with piecewise linear interface calculations method (PLIC). This interface reconstruction is applied to simulate the time evolution of the dynamics of drop of surfactants spreading on thin water liquid substrates. In the model, the surfactant is considered as a separate phase instead of a solution of water containing the surfactant. This approach allows to avoid the parallel determination of the surfactant molecular diffusion coefficient, the maximum packing concentration, and the rate constants for adsorption and desorption prior to the simulations. Series of superspreader trisiloxane (M(D′EnOH)M surfactant are considered. The predictions of the CFD model agree remarkably well with the measurements from previously published experimental results. The simulations are used to predict and optimize the spreading behavior as a function of a range of well-defined parameters including the water/surfactant interfacial tension (28−35 mN/m), the volume of the drop of surfactant (0.61−38.79 mm3) and the thickness of the water layer (1−3 mm). The dewetting process of the thin water layer from the surface by the surfactant occurs for almost all the configurations. The formation of secondary drops and instable crown happen solely for the largest drop volume of 38.79 mm3. Only for the thicker films (h = 2 and 3 mm), a cavity on the liquid is generated after the impact. For all the thicknesses, instabilities appear at the surfactant/water interfaces and their numbers are larger for the thinner film (h = 1 mm). The kinetic analysis of the numerical data confirms the existence of two successive spreading regimes for all the drops of surfactants studied. The faster time evolution of the moving front proceeds for surfactant drops of low volume and high surface tension as well as a thick water underlayer.

Quantitative nanoscale tracking of oxygen vacancy diffusion inside single ceria grains by in situ transmission electron microscopy

Oxygen vacancy formation and migration in ceria is critical to its electrochemical and catalytic properties in systems for chemical and energy transformation, but its quantification is rather challenging especially at atomic-scale because of disordered distribution. Here we report a rational approach to track oxygen vacancy diffusion in single grains of pure and Sm-doped ceria at −20 °C to 160 °C using in situ (scanning) transmission electron microscopy ((S)TEM). To create a gradient in oxygen vacancy concentration, a small region (∼30 nm in diameter) inside a ceria grain is reduced to the C-type CeO1.68 phase by the ionization or radiolysis effect of a high-energy electron beam. The evolution in oxygen vacancy concentration is then mapped through lattice expansion measurement using scanning nano-beam diffraction or 4D STEM at a spatial resolution better than 2 nm; this allows direct determination of local oxygen vacancy diffusion coefficients in a very small domain inside pure and Sm-doped ceria at different temperatures. Further, the activation energies for oxygen transportare determined to be 0.59, 0.66, 1.12, and 1.27 eV for pure CeO2, Ce0.94Sm0.06O1.97, Ce0.89Sm0.11O1.945, and Ce0.8Sm0.2O1.9, respectively, implying that activation energy increases due to impurity scattering. The results are qualitatively supported by density functional theory (DFT) calculations. In addition, our in situ TEM investigation reveals that dislocations impede oxygen vacancy diffusion by absorbing oxygen vacancies from the surrounding areas and pinning them locally. With more oxygen vacancies absorbed, dislocations show extended strain fields with local tensile zone sandwiched between the compressed ones. Therefore, dislocation density should be reduced in order to minimize the resistance to oxygen vacancy diffusion at low temperatures.

Effect of Bridgehead Methyl Substituents on the Gas Permeability of Tröger's-Base Derived Polymers of Intrinsic Microporosity.

A detailed comparison of the gas permeability of four Polymers of Intrinsic Microporosity containing Tröger’s base (TB-PIMs) is reported. In particular, we present the results of a systematic study of the differences between four related polymers, highlighting the importance of the role of methyl groups positioned at the bridgehead of ethanoanthracene (EA) and triptycene (Trip) components. The PIMs show BET surface areas between 845–1028 m2 g−1 and complete solubility in chloroform, which allowed for the casting of robust films that provided excellent permselectivities for O2/N2, CO2/N2, CO2/CH4 and H2/CH4 gas pairs so that some data surpass the 2008 Robeson upper bounds. Their interesting gas transport properties were mostly ascribed to a combination of high permeability and very strong size-selectivity of the polymers. Time lag measurements and determination of the gas diffusion coefficient of all polymers revealed that physical ageing strongly increased the size-selectivity, making them suitable for the preparation of thin film composite membranes.

Determination of Diffusion Coefficients and Antioxidant Activities of Ascorbic Acid in Guava Juice using Cyclic Voltammetry

Ascorbic acid is the most abundant antioxidant present in guava (Psidiumguajava L.). There had only been few studies concerning the determination of diffusion coefficient and antioxidant activity of ascorbic acid in guava juice using cyclic voltammetry specifically at varying temperatures. Thus, this study on the effect of temperature on diffusion coefficient and antioxidant activity on ascorbic acid found in guava was done using cyclic voltammetry. The temperatures tested were at 15°C, 25°C, 36°C, and 45°C. Electrodes used in the experiment were glassy carbon as the working electrode, platinum wire as the counter electrode, and Ag/AgCl electrode as the reference electrode. The results showed that the peak currents of ascorbic acid in guava juice at 15°C, 25°C, 36°C, and 45°C were -0.5720, -0.5380, -0.5000, and -0.4760 μA, respectively. The diffusion coefficients of the ascorbic acid were obtained using the Randles-Sevcik equation at all given temperatures and the values were 2.1489 x10−5, 2.1711 x10−5, 2.2070 x10−5, and 2.2250 x10−5 cm2/s, respectively. The antioxidant activities, in terms of concentration, at the said temperatures were found to be 0.3374, 0.3212, 0.3015, and 0.2899 mM, respectively. It is concluded that at higher temperature, ascorbic acid in guava juice has a higher diffusion coefficient but lower antioxidant activity. The present results can be used by other researchers doing similar work on fate and transport of the studied system.

Optimization of electrochemical time of flight measurements for precise determinations of diffusion coefficients over a wide range in various media

Diffusion coefficients are an important physical property to both physical and analytical electrochemistry and the role they play in sensors, batteries, and catalysis. In electrochemical time of flight (ETOF), the time needed for an electrochemically generated species to travel to an adjacent electrode is measured. Previously relegated to verifying diffusion modeling and theoretical work, ETOF is a powerful and elegant technique whose broad applicability has been overlooked. In the determination of diffusion coefficients, ETOF does not require setting delicate hydrodynamic conditions required by rotating ring disk (RDE) methods. In addition, no foreknowledge about the complete electrochemical mechanistic system, nor about its electron stoichiometry is required. ETOF is ideal for determining the diffusion coefficients for non-elucidated systems, such as for short-lived intermediates assuming they survive ETOF travel time. Here we report the construction of a universal empirical calibration curve for the determination of diffusion coefficients using experimental parameters optimized by computer modeling. Using a platinum micro electrode array, diffusion coefficients were determined for a variety of species including ferrocenium, ruthenium (III) bisbipyridine dichloride, and vanadium (III) acetylacetonate, some of which being previously unreported. The elegance of the method is that the calibration curve constructed with a few well-established species in a given electrolyte can be used for any species in any electrolyte.

Technical note: Determination of binary gas-phase diffusion coefficients of unstable and adsorbing atmospheric trace gases at low temperature – arrested flow and twin tube method

Abstract. Gas-phase diffusion is the first step for all heterogeneous reactions under atmospheric conditions. Knowledge of binary diffusion coefficients is important for the interpretation of laboratory studies regarding heterogeneous trace gas uptake and reactions. Only for stable, nonreactive and nonpolar gases do well-established models for the estimation of diffusion coefficients from viscosity data exist. Therefore, we have used two complementary methods for the measurement of binary diffusion coefficients in the temperature range of 200 to 300 K: the arrested flow method is best suited for unstable gases, and the twin tube method is best suited for stable but adsorbing trace gases. Both methods were validated by the measurement of the diffusion coefficients of methane and ethane in helium and air as well as nitric oxide in helium. Using the arrested flow method the diffusion coefficients of ozone in air, dinitrogen pentoxide and chlorine nitrate in helium, and nitrogen were measured. The twin tube method was used for the measurement of the diffusion coefficient of nitrogen dioxide and dinitrogen tetroxide in helium and nitrogen.

Determination of mobility and diffusion coefficients of Ar+ and Ar2+ ions in argon gas

It has recently been shown that accurate theoretical calculations can be used to calibrate a drift-tube mass spectrometer (DTMS) to measure gaseous ion mobilities accurate to within 0.6%. Here we present a new method for calibrating a DTMS instrument to obtain diffusion coefficients parallel to the electric field which are accurate to within 8%. This method is developed and verified by consideration of He+ (2S1/2) ions in He. We apply these techniques to determine transport coefficients for Ar+(2P3/2) and Ar2+ (3P2,1,0) ions in Ar gas at 300 K, with results given as a function of E/N, the ratio of electrostatic field strength to gas number density, in the range 30–210 Td. The measured mobilities are accurate within 0.8%; for Ar+ they agree within 1.5% with Monte Carlo simulations, and for both the cations and dications they are in excellent agreement with previous measurements. Our method gives new diffusion coefficients that agree within 5% with quantum Monte Carlo calculations.

Rapid determination of diffusivity in massive anisotropic porous materials

A method for rapid determination of diffusion coefficients of polar solvents in anisotropic porous materials, making it possible to control the state of products prepared from such materials without destruction, is reported. For implementation of the proposed method, no preliminary calibration of the local solvent concentration in solid phase for the used converter and each new “porous material-solvent” system is required; that circumstance largely increases the research productivity of the method. The method possesses flexibility in terms of the possibility for measuring the values involved in the calculation expression on curve sections with a high sensitivity to parameter changes and in the range with a stable and noise-protected output signal of the concentration converter, which fact ensures an in-creased control accuracy.

Moisture diffusion in plasma-enhanced chemical vapor deposition dielectrics characterized with three techniques under clean room conditions

Absorption of moisture by thin dielectric materials alters their properties and can cause several reliability issues. Even at standard room temperature and low humidity level, some dielectric materials are sensitive to moisture. In this study, moisture diffusion in two plasma-enhanced chemical vapor deposition (PECVD) films is investigated with three measurement methods to determine diffusion coefficients and saturated moisture concentrations: mass measurements, bending radius of curvature measurements and infrared spectroscopy. The two PECVD silicon dioxides are deposited at 200 °C and 400 °C. They were exposed to moisture in clean room environment (21 °C and 40% relative humidity) for about 800 h. The present results confirm that mass measurements, bending radius of curvature measurements and infrared spectroscopy can be used to monitor thin dielectric films in these environmental conditions. They lead to similar values for the diffusion coefficient. These values are in the range of [1.5–4.2] × 10−15 cm² s−1 for the 200 °C film and [2.3–3.6] × 10−15 cm² s−1 for the 400 °C one. Saturated moisture concentrations confirm that the two dielectrics are sensitive to moisture even at 21 °C, 40% relative humidity. Besides, the results show that standard fickean behavior does not provide the best fit to model water diffusion for some dielectric films. A dual stage model that appears to be more adapted is finally introduced.

Impedance studies of Li+ diffusion in nickel manganese cobalt oxide (NMC) during charge/discharge cycles

Abstract One of the diagnostic tools of lithium-ion batteries aging process is the determination of the solid-state lithium ion diffusion coefficient. This parameter was calculated for LiNi1/3Mn1/3Co1/3O2 secondary particles. Electrochemical impedance spectroscopy of three-electrode Swagelok cells was used to monitor the evolution of parameters such as the contact resistance, the charge transfer resistance, the double layer capacitance and the lithium ion diffusion coefficient as functions of the open circuit voltage while charging and discharging. The effect of higher cut-off voltages on these parameters was also studied. Phenomena such as transition metal dissolution and oxygen release are suggested to be more predominant at these higher cut-off potentials. They have a significant effect on the lithium ion diffusion path inside the cathode particles and thus diminish the lithium ion diffusion coefficient.

Evaluation of the Mass Diffusion Coefficient and Mass Biot Number Using a Nondominated Sorting Genetic Algorithm

A precise determination of the mass diffusion coefficient and the mass Biot number is indispensable for deeper mass transfer analysis that can enable finding optimum conditions for conducting a considered process. The aim of the article is to estimate the mass diffusion coefficient and the mass Biot number by applying nondominated sorting genetic algorithm (NSGA) II genetic algorithms. The method is used in drying. The maximization of coefficient of correlation (R) and simultaneous minimization of mean absolute error (MAE) and root mean square error (RMSE) between the model and experimental data were taken into account. The Biot number and moisture diffusion coefficient can be determined using the following equations: Bi = 0.7647141 + 10.1689977s − 0.003400086T + 948.715758s2 + 0.000024316T2 − 0.12478256sT, D = 1.27547936∙10−7 − 2.3808∙10−5s − 5.08365633∙10−9T + 0.0030005179s2 + 4.266495∙10−11T2 + 8.33633∙10−7sT or Bi = 0.764714 + 10.1689091s − 0.003400089T + 948.715738s2 + 0.000024316T2 − 0.12478252sT, D = 1.27547948∙10−7 − 2.3806∙10−5s − 5.08365753∙10−9T + 0.0030005175s2 + 4.266493∙10−11T2 + 8.336334∙10−7sT. The results of statistical analysis for the Biot number and moisture diffusion coefficient equations were as follows: R = 0.9905672, MAE = 0.0406375, RMSE = 0.050252 and R = 0.9905611, MAE = 0.0406403 and RMSE = 0.050273, respectively.

In-situ monitoring of moisture diffusion process for wood with terahertz time-domain spectroscopy

The moisture diffusion process in balsa wood was monitored using the terahertz time-domain spectroscopy (THz-TDS) technique. The reflective THz signals were measured during the drying and the absorption phase of the moisture in the balsa wood. Measurements were conducted along the direction of the wood grain (longitudinal) and perpendicular to the direction of the wood grain (tangential). From the results, the relationship between the pulse intensity of the THz signal and moisture content was quantitatively investigated. Further, an image of the moisture concentration gradient was constructed through the THz intensity analysis. From the study, it was possible to monitor the variation of diffusion coefficient depending on the moisture content gradient from the THz measurement. Moreover, using the measured concentration gradient, the moisture diffusion coefficient could be derived regardless of complicated boundary conditions of diffusion. Consequently, the degree of moisture diffusion can be successfully measured using the THz-TDS technique. This can then be utilized for the determination of the moisture diffusion coefficient in various industrial structures.

Determination of the Diffusion Coefficient of Supercritical CO2 in Low-Permeability Formation Cores

CO₂ diffusion in the oil phase in the presence of porous media is of great importance to forecast the performance of enhanced oil recovery and carbon dioxide capture and storage. When CO₂ is brought into contact with an oil phase, diffusion occurs. The indirect pressure-decay methodology has been applied successfully to determine the mutual diffusion coefficients of supercritical CO₂ and crude oil at temperature of 65 °C. Theoretically, a one-dimensional double-way mass transfer model incorporating the capillary and adsorption effects of porous media has been constructed to quantify the mutual dynamic diffusion coefficients. The crude oil has been characterized into five pseudo-components for the accurate description of the phase behavior of CO₂ gas and oil phases. An optimization method along with the PR equation of state is employed to determine each component’s diffusion coefficients in the gas and oil phases for the purpose of minimization of the difference between the experimental data and calculated results. Satisfactory agreements are obtained with a merely 0.97% pressure difference when a variable diffusion coefficient is implemented. The short-time experimental test and a long-time-duration calculation are recommended for further diffusion investigation. The capillary analysis gave a regressed fractal dimension of 2.7049 with the average absolute deviation of 0.602%. The adsorption phenomenon can be greatly influenced by the existence of heavy components. The heavier the components, the greater their impact on adsorption. Furthermore, a faster and enhanced diffusion process is observed at high pressure and temperature. The combination of several complex mechanisms leads to the initial gradual increase of the diffusion coefficient with time, and then, it arrives at a plateau, which is slightly different from the previous diffusion coefficient changing tendency mentioned in the literature. In the presence of a low-permeability formation core, the determined diffusion coefficients of CO₂ in the gas and liquid phases are increased from 4.38 × 10–⁹ to 6.21 × 10–⁹ and 6.16 × 10–¹⁰ to 9.21 × 10–¹⁰ m²/s when the system pressure is decreased from 18.2 to 12.11 MPa, respectively. In addition, the capillary effect can lead to a reduction of the diffusion coefficient in the oil phase but has little effect on the diffusion coefficient in the gas phase.

Effect of dilution on particle size analysis of w/o emulsions by dynamic light scattering

Dynamic Light Scattering (DLS) is a well-known (sub)micron particle size analysis technique. As such, it should be a valuable technique for water droplet size determination in (sub)micron water-in-oil emulsions. In this study, the sample pretreatment conditions were optimized in order to enable accurate droplet size determination by DLS. Whereas DLS was indeed capable of detecting differences between differently produced (sub)micron sized w/o emulsions, it was observed that the estimated droplet size was highly influenced by the measurement conditions used. First of all, the experimentally determined diffusion coefficient decreased with increasing water droplet concentration, which is thought to be due to interaction effects between the water droplets. To minimize this effect, the used concentration should be as low as possible. However, in doing so, the water droplets were frequently observed to disappear during storage or even during analysis, due to their dissolution in the dilution medium. The latter disturbing effect could be avoided by (sufficient) water saturation of the dilution medium and preventing water evaporation by closing the diluted sample and by restricting the head space. Summarizing, (sub)micron water droplets can be characterized using DLS. However, careful selection of the sample preparation and measurement conditions is necessary to obtain reliable data.