Determination Of Diffusion Coefficients Research Articles

Simultaneous determination of the radon diffusion coefficient and the free radon production rate from compact porous emanation media

The radon diffusion coefficient and the free radon production rate are important parameters for used to describe the migration of radon in porous emanation media. However, the method currently used to determine these two parameters is complicated. Based on a theory of the radon exhalation by diffusion from the inner and outer surfaces of a circular tube, a method to determine these two parameters in compact porous emanation media was proposed, and an experimental measuring device was designed and manufactured. The experimental device was used to simultaneously measure the radon exhalation rate from the inner and outer surfaces of a quarter-circular tubular concrete block filled with fine-grained uranium tailing sand. The measurements were used to calculate the radon diffusion coefficient and the free radon production rate. The result obtained by using this method shows that accuracy was within the accepted range of experimental error. This method has practical value for the simultaneous determination of the radon diffusion coefficient and the free radon production rate from compact porous emanation media.

Mathematical model, validation and analysis of the drying treatment on quality attributes of chicory root cubes considering variable properties and shrinkage

This work presents an exhaustive three dimensional mathematical model to describe chicory root cubes drying process (Cichorium intybus L.) using a Fick’s diffusion model considering a variable diffusion path length in three dimensions. Experimental data obtained at laboratory scale is used to validate the proposed model. Experiments are conducted using a forced convection laboratory dryer at temperatures of 60°C and 80°C and air velocities of 0.2 and 0.7m/s to dry chicory root cubes of 1cm of side. Mathematical modeling is firstly used to represent the performance of the drying process with the temporal variations of the average humidity content, to determine diffusion coefficients, and afterwards, to obtain useful predictions on how the volumetric contraction of the cubes behaves under different operating conditions. The good agreements between experimental and predicted values prove that the proposed model can be applied to the precise description of experimental drying curves for chicory roots in three dimensions (3-D). In the ranges covered, the values of the effective moisture diffusivity were obtained between 5.63×10−5 and 8.21×10−5cm2/s. Results from the analysis of rehydration and browning aspects illustrate that drying conditions have effects on the quality attributes of the dried samples.

Compatibility of Natural Dyes on Aluminum Pre-Mordanted Woolen Yarns by Determination of Diffusion Coefficient

In the present research, a method of assessing relative compatibility rating of single and binary mixtures of walnut green shell, cochineal, and weld natural dyes on aluminum pre-mordanted woolen yarns was proposed, where a proportion of the calculated diffusion coefficients of dyes was postulated. To calculate the diffusion coefficient values, the uptake behavior of dyes was derived as the K/S and the exhaustion curves by dyeing the woolen yarn samples with the individual dye as well as with the mixtures of dyes obtained from practical conditions of dyeing. A typical method was employed to dye the samples at two temperatures of 80 and 95 oC. The method proposed for determination of the compatibility of dyes was more verified at higher temperature, that is, 95 oC, against a conventional method of solution analysis. The results of compatibility showed that the selected binary mixtures of cochineal-weld have an excellent compatibility. The other mixtures, that is, walnut green shell-cochineal and walnut green shell-weld showed weak-moderate and very weak compatibility, respectively.

AUC measurements of diffusion coefficients of monoclonal antibodies in the presence of human serum proteins.

The goal of this work is to develop a preclinical method for quantitative hydrodynamic and thermodynamic analysis of therapeutic proteins in crowded environments like human serum. The method utilizes tracer amounts of fluorescently labeled monoclonal antibodies and the Aviv AU-FDS optical system. We have performed sedimentation velocity experiments as a function of mAb, human serum albumin and human IgG concentration to extract self- and cross-term hydrodynamic nonideality effects. SV measurements are consistently complicated by weak mAb-mAb and mAb-IgG interactions (Wright et al. in Anal Biochem 550:72-83, 2018). In an attempt to explore different approaches we have investigated measurements of diffusion coefficients by traditional synthetic boundary experiments. Here we present a new technique incorporated into SEDANAL that can globally analyze the full time course of synthetic boundary experiments. This approach also utilizes F-mAb against a high concentration of unlabeled carrier protein (HSA or IgG). In principle both diffusion and sedimentation coefficient information can be extracted including hydrodynamic and thermodynamic nonideality. The method can be performed at a traditional low speed (5-7Krpm) or at high speeds. The high speed method can also be used to measure D and s for small molecules like fluorescein (often contaminants of F-HSA and F-mAb). The advantage of synthetic boundary over the standard sedimentation velocity method is that it allows for higher precision determination of diffusion coefficients. The concentration dependence of D can be corrected for hydrodynamic nonideality effects by plotting D * (1 + kijcj) vs total carrier concentration. The slope of the fitted data allows an alternate approach to determine self- and cross-term thermodynamic nonideality. This method can also explore cross-term diffusion coefficient effects. These results are compared to dynamic light scattering approaches which are limited to kD determinations for solutions of pure protein.

Grain-boundary diffusion coefficient in α-Al2O3 from spark plasma sintering tests: Evidence of collective motion of charge disconnections

The sintering of fine-grained α-alumina by spark plasma sintering (SPS) was performed to study grain growth under SPS conditions. Grain growth is found to be extensive at relative densities above 95%. A grain growth versus dwell time analysis during SPS allows for the determination of the grain-boundary diffusion coefficient. This study shows that the remarkable enhancement of grain-boundary diffusion derived from a previous analysis could be a consequence of the presence of the recently discovered “disconnections” at the grain boundaries of α-alumina. Their presence, together with their electric charge and the external electric field at the boundaries, are the key ingredients for a violation of the typical grain growth kinetic law. When they are introduced appropriately, an updated value of the grain-boundary diffusion coefficient is achieved. A comparison with other values reported previously in the literature through other techniques and a critical analysis are also carried out.

Krypton-methanol spectroscopic study: Assessment of the complexation dynamics and the role of the van der Waals interaction

The Kr–CH3OH (Krypton–Methanol) system has several technological applications, such as the determination of diffusivity coefficients, their use in the development of detectors and combustion techniques among others. We report an extensive theoretical study concerning the stability of such complex. A mix between molecular dynamics, electronic structure calculations and solution of the nuclear Schrodinger equation lead to investigation of spectroscopic constants, lifetime of the complex and its Quantum Theory Atom in Molecules (QTAIM) properties. The study of the Potential Energy Curves (PEC) suggested three configurations to be stable as their potential well were able to harbor 9 vibrational levels. Properties from the curves also allowed us to obtain the lifetime of the complex, whose values were >1 ps regardless of the conformation. Furthermore, topological investigations of the charge density profile of the complex, in the scope of QTAIM properties, show that van der Waals type interactions takes place between the noble gas and the methanol molecule. These features are in consonance to the experimental fact that this complex is stable.

Method of non-destructive control of the solvent diffusion coefficient in products made from anisotropic porous materials

The development of methods and means of non-destructive products testing in various industries is an actual task. The subject of this study is non-destructive testing of the solvents mass transfer processes in products made from anisotropic porous materials (PM) and the diffusion coefficient determination. The known methods for determining the diffusion coefficient in anisotropic porous media are developed for canonical forms. This leads to the necessity of destroying products for making experimental samples from them of a given configuration and size. The purpose of this study is to develop a dynamic method that allows us quickly determine the diffusion coefficient in products from anisotropic porous materials without destroying them. The method is designed to investigate the diffusion coefficient of solvents, for example, in reinforced building elements from materials having a porous structure. The task of constructing the method mathematical model is solved. The influence of the design and operating measuring device parameters on the accuracy of the determining diffusion coefficient is studied. A theoretical estimate of the error in the measurement result was made. The results of the method application are presented.

Effects of anisotropy and regime of diffusion on the measurement of lattice diffusion coefficient of hydrogen in metals

The lattice diffusion coefficient of hydrogen in metals is commonly measured by permeation tests. Such tests assume isotropic diffusivity with a set-up which measures permeation flux only along one direction. The measured values of the lattice diffusion coefficient are strongly influenced by the trapping of hydrogen at microstructural defects. These factors lead to highly inaccurate determination of the lattice diffusion coefficient, more so in an anisotropic medium. In this work, we present a three-dimensional (3D) diffusion equation in non-dimensional form for an anisotropic medium with source and sink terms which account for detrapping and trapping of hydrogen. The concentration of hydrogen at lattice and trap sites is assumed to be in a local equilibrium. An initial boundary value problem of the permeation test is formulated and the governing partial differential equation is implemented in a 3D finite-element code. The influence of anisotropic diffusivity on the measurement of lattice diffusion coefficient is shown by numerical simulations. Asymptotic analysis of the governing equation reveals that the lattice diffusion coefficient can only be measured in certain regimes when performing permeation tests at varying temperatures. The nonlinear behaviour of Arrhenius plots of diffusion coefficient versus inverse of temperature due to trapping is analytically and numerically predicted.

Time-resolved impact electrochemistry - A new method to determine diffusion coefficients of ions in solution

Diffusion is often the rate-limiting factor of reactions in condensed phase. Thus, knowing the diffusion coefficient is key in numerous aspects ranging from drug release to steering of reactions in both homogeneous liquid phase and electrochemical reactions. Cyclic voltammetry at macro electrodes and chronoamperometry at micro electrodes are well-established methods to determine the diffusion coefficients of redox-active species dissolved in a solution. However, if the formal potentials of the redox species are outside of the potential window of the solvent, then these methods cannot be readily applied. Here we demonstrate a new concept to determine the diffusion coefficient of ions to overcome this limitation. We use their reaction with a well-defined amount of a redox-active indicator substance, which is confined in a nanoparticle suspended in a solution containing the species of interest. Employing transformative nanoparticle impact analysis, the diffusion-limited reaction of an indicator nanoparticle with the species of interest is initiated and followed by chronoamperometry. Measuring the time it takes to fully convert the indicator particle enables the determination of the diffusion coefficient of interest. This concept is demonstrated for variety of (pseudo-)halides in aqueous solution using Ag nanoparticles as redox indicator. Using chloride as an example, is further shown that this new methodology can be applied to study effects of temperature and viscosity on the diffusion coefficients. Given the multitude of nanoparticles that may serve as electrochemical redox indicator, this approach can be used to determine the diffusion coefficients for a large variety of species in different liquid environments.

Possibility of determination of transport coefficients D and k from relaxation experiments for sphere-shaped powder samples

Precise determination of chemical diffusion coefficient D and surface exchange reaction coefficient k is of importance for characterization of materials exhibiting ionic or mixed ionic-electronic type conductivity. Commonly performed as relaxation-type experiments, such studies require well-defined geometry of the considered samples. Also, additional constrains regarding magnitude of changes of concentration of the mobile species, as well as values of dimensionless parameter L, in the case of simultaneous determination of D and k, have to be fulfilled. In this work, the application of relaxation-type experiments for evaluation of transport coefficients in the case of studies of powders with different grain size is discussed. Numerical diffusion solutions for the application of particle powders are proposed, which allow to determine the transport diffusion coefficients D and k for powdered materials. The case study of diffusion coefficients D and k with the proposed numerical diffusion solutions is performed for LiCoO2 powder-shaped material in lithium-ion batteries by the modified-PITT method. In addition, a systematic discussion of the mathematical basis of the relaxation methods, with three typical cases (diffusion-controlled, surface exchange reaction-controlled and mixed process) is given, with particular attention directed to the role of the dimensionless parameter L.

Development of Anodic Stripping Voltammetry in Alkaline Electrolyte and Application for Screening Anion Diffusion Selectivity in Battery Separators

Anodic stripping voltammetry (ASV) is a well-known powerful, sensitive, and selective analysis technique used for the detection of metal ion species in solution. While ASV was initially developed with mercury (Hg) as the plating electrode more recent applications have used bismuth (Bi) as a less toxic and less oxygen sensitive electrode that has low background currents, better reproducibility, and little to no need for electrode conditioning, as compared to Hg electrodes. ASV is most commonly performed under neutral to acidic electrolyte conditions where metals, as metal cations are readily soluble; however, the extension of an ASV method into highly alkaline environments (pH > 14) could prove useful for the in situ electrolyte monitoring of alkaline batteries and fuel cells such that potential diagnostics of their performance vs. electrolyte composition could be realized. With this in mind, we recently extended the ASV method to highly alkaline electrolytes, in order to determine Zn diffusion across separator membranes.[1] Zinc (Zn) alkaline battery chemistries such as Zn/MnO2 and Zn/Air are currently attracting a lot of attention due to their potential as safe, low cost, high energy density rechargeable batteries. A main failure mechanism for these cells is the poisoning of the cathode material during cycling due to Zn crossover from the anode to the cathode. Advanced separators that successfully stop or limit this crossover are crucial in order to increase the cycle lifetime of these batteries. ASV, utilizing a Bi film, along with cadmium (Cd) and lead (Pb) as the plating mediators, was utilized to determine Zn concentrations in highly alkaline environments (30% NaOH or 35% KOH). To evaluate the utility of this assay, zincate diffusion through commercial off-the-shelf (COTS) Celgard 3501 and Cellophane 350P00 membranes was monitored using both ASV and inductively coupled plasma – mass spectrometry (ICP-MS) methods. The obtained zincate diffusion coefficients for both techniques are shown to compare favorably. While the traditional complexometric or elemental analysis methods can take days to weeks to determine Zn membrane diffusion metrics, this ASV method provides a real-time measurement which significantly increases the throughput for the screening of these membranes. During our development of an ASV method for Zn, we realized that in general there was a lack of ASV methods in highly alkaline electrolyte and hence turned our attention to the development of an ASV method for the determination of Cu, as cuprate [Cu(OH)4 2-]. Cu has been notoriously difficult to measure by ASV, even under acidic conditions.[2] In fact, most studies using Bi film electrodes for the direct determination of Cu have deemed it impossible and thus studies for the determination of the Cu concentration in a matrix are normally still performed separately with Hg electrodes. After investigation of potential metal film electrodes and mediators including Cd, Ag, Sb, and Zn, it was found that lead (Pb) serves as a good mediator for the plating of Cu in highly alkaline solutions which permits the replacement of the interfering Bi film electrode. Various aspects of this work will also be presented. [1]. J. Duay, T. N. Lambert and R. Aidun “Stripping Voltammetry for the Real Time Determination of Zinc Membrane Diffusion Coefficients in High pH: Towards Rapid Screening of Alkaline Battery Separators” Electroanalysis 2017, 29, 2261-2267. [2]. J. Duay, J. E. Ortiz-Santiago and T. N. Lambert “Copper Sensing in Alkaline Electrolyte Using Anodic Stripping Voltammetry by means of a Lead Mediator” Electroanalysis 2017, DOI: 10.1002/elan.201700526. This work was supported by the Laboratory Directed Research and Development program at Sandia National Laboratories. Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525. Dr. Imre Gyuk, Energy Storage Program Manager, Office of Electricity Delivery and Energy Reliability is also thanked for financial support of this project.

Semi-Integral Electroanalysis of the Electrochemistry of Tris(2,2`-bipyridine) Complexes

The 2,2`-bipyridine (bpy) ligand is one of the most widely used in coordination chemistry. It was first synthesized at the end of the 19th century, with the iron(II) tris(bpy) being the first complex of this ligand ever observed1. Over the years a diversity of metals complexed with bpy have been synthesized and extensively studied, and recently some applications of these complexes have been proposed, e.g. the use of iron (II) and nickel (II) tris(bpy) complexes for non-aqueous electrolytes of batteries2 and the use of cobalt (II) tris(bpy) for thermo electrochemical cells3. Also, currently there is a growing interest in using ionic liquids (ILs) for electrochemical applications, because these compounds, broadly defined as salts that are liquid at or close to room temperature, usually present some interesting properties, such as low volatility, non-flammability and intrinsic ionic conductivity. The semi-integral electroanalysis is a powerful method for investigating the kinetics of redox reactions and determining the diffusion coefficients4 and was used to aid the interpretation of the electrochemical behaviour of tris(bpy) complexes. The purpose of this work was to study the electrochemistry of the tris(bpy) complexes of cobalt (II)5, nickel (II) and iron (II)6 in ILs and organic solvents, thus contributing to the understanding of how these compounds behave in these media. Four ILs (two having the imidazolium cation and two the pyrrolidinium cation) and three organic solvents were used and the basic electrochemical properties of these complexes were investigated, including the redox potentials and the chemical and electrochemical reversibility of the redox reactions, as well as the kinetics of the oxidation reactions. The semi-integral electroanalysis was used for determining diffusion coefficients and for a qualitative analysis of the reversibility of the redox reactions. E. C. Constable, in Adv. Inorg. Chem., ed. A. G. Sykes, Academic Press, 1989, vol. Volume 34, pp. 1-63.J. Mun, M.-J. Lee, J.-W. Park, D.-J. Oh, D.-Y. Lee and S.-G. Doo, Electrochem. Solid-State Lett., 2012, 15, A80-A82.M. A. Lazar, D. Al-Masri, D. R. MacFarlane and J. M. Pringle, PCCP, 2016, 18, 1404-1410.K. B. Oldham, Journal of Electroanalytical Chemistry and Interfacial Electrochemistry, 1976, 72, 371-378.D. Cabral, P. C. Howlett, J. M. Pringle, X. Zhang and D. MacFarlane, Electrochim. Acta, 2015, 180, 419-426.D. M. Cabral, P. C. Howlett and D. R. MacFarlane, Electrochim. Acta, 2016, 220, 347-353.

Influence of water absorption on chosen strength properties of single-polymer polyester composites

Investigations of the selected properties of single-polymer polyester composites (SPC) in dry condition and immersed in water are presented. Materials were tested for possible applications in shipbuilding. Water absorption till saturation limit was examined, at temperatures of 3, 23 and 100 °C, through the determination of water diffusion coefficient. Some material properties were determined through impact resistance tests of materials varyingin fiber content [0 (A), 5 (B), 10 (C), 15 (D), 20 wt % (E)]. The highest impact resistance (6 J/cm2) was found for the composite with more than 15 % of reinforcement in dry condition.

Comparative electrochemical studies of kinetic and thermodynamic parameters of Quinoxaline and Brimonidine redox process

The electrochemical response of two biologically important benzopyrazine derivative, Quinoxaline and Brimonidine (5-bromo-N-(4,5-dihydro-1H-imidazol-2-yl)quinoxaline-6-amine) was studied at glassy carbon electrode. Investigations were performed in acetate buffer at pH 3.6 where both compounds undergo complex electrode process which begins with quasi reversible redox process at pyrazine ring forming di-hydro derivative, which is further irreversible oxidized to hydroxyl-derivative. Cyclic voltammetry at different scan rates was employed for the determination of heterogeneous electron transfer rate constant and diffusion coefficient of the compounds. The values of electron transfer rate constant at different temperatures were used for the evaluation of thermodynamic parameters like enthalpy, entropy and Gibbs free energy changes, as well as apparent energy of activation.Computational study has been performed in order to evaluate some useful quantum chemical parameters with the aim to confirm and explain the difference in experimentally obtained kinetic and thermodynamic parameters of the investigated QUI and BRIM redox process. Results were compared with studies of similar compounds and pointed out the observed similarities and differences.

Diffusivity optimization of supercritical carbon dioxide extraction with co-solvent-ethanol from peanut skin

Peanut skin is a waste of industrial peanut butter that contains bioactive compound, which is used as antioxidant, anti-diabetic, anti-cancer, and anti-inflammatory. Supercritical carbon dioxide (SC-CO 2 ) extraction as green technology is applied to extract peanut skin oil. The aim of this study is to optimize the operational conditions of pressure, temperature, and percentage of co-solvent to obtain oil yield and diffusivity coefficient. Determination of diffusivity coefficient was needed to evaluate the mass transfer between solvent and solute. The operational conditions of SC-CO 2 studied were different pressure (10, 20, 30 MPa), different temperature (40, 55, 70 °C and different co-solvent percentage (2.5, 5, and 7.5 % (V ethanol /V solvent )). The extraction time was 3 hours respectively. The optimum condition were 29.95 MPa, 40 °C and 6.49 % (V ethanol /V solvent ) with 14.95 % yield and 8.47E-12 m 2 /s diffusivity coefficient.

Computational Signaling Protein Dynamics and Geometric Mass Relations in Biomolecular Diffusion.

We present an atomistic level computational investigation of the dynamics of a signaling protein, monocyte chemoattractant protein-1 (MCP-1), that explores how simulation geometry and solution ionic strength affect the calculated diffusion coefficient. Using a simple extension of noncubic finite size diffusion correction expressions, it is possible to calculate experimentally comparable diffusion coefficients that are fully consistent with those determined from cubic box simulations. Additionally, increasing the concentration of salt in the solvent environment leads to changes in protein dynamics that are not explainable through changes in solvent viscosity alone. This work in accurate computational determination of protein diffusion coefficients led us to investigate molecular-weight-based predictors for biomolecular diffusion. By introducing protein volume- and protein surface-area-based extensions of traditional statistical relations connecting particle molecular weight to diffusion, we find that protein solvent-excluded surface area rather than volume works as a better geometric property for estimating biomolecule Stokes radii. This work highlights the considerations necessary for accurate computational determination of biomolecule diffusivity and presents insight into molecular weight relations for diffusion that could lead to new routes for estimating protein diffusion beyond the traditional approaches.

Determination of diffusion coefficients of supercritical CO2 under tight oil reservoir conditions with pressure-decay method

A generalized methodology has been developed to determine the diffusion coefficients of supercritical CO2 under tight oil reservoir conditions considering the oil swelling effect. Experimentally, a diffusion cell has been used to perform diffusion tests for CO2 in tight formation cores, saturated with crude oil, under different pressure and temperature values. The dynamic pressure-decay curves of CO2 in the annular space of the diffusion cell were monitored and recorded during the measurements. Theoretically, the Peng–Robinson equation of state (PR EOS) with a modified α function has been incorporated to develop a one-dimensional radial diffusion model for the CO2–tight formation core systems. Also, the crude oil sample has been characterized as three pseudo-components for the accurate prediction of phase behavior of the CO2 and crude oil system. The CO2 diffusion coefficients, under different pressure and temperature values, were determined once the discrepancy between the measured and the calculated times, under the same pressure decrease of the diffusion process was minimized. According to the CO2 concentration profiles in the cores, the diffusion process is divided into two distinct parts, i.e., the early stage, characterized by the fast diffusion rate, and the later stage with the slow diffusion rate. While the pressure and the temperature increase, the CO2 diffusion coefficient initially increases quickly and then reaches a plateau. Lower viscosity of crude oil, higher temperature, and higher pressure facilitate the diffusion of CO2 into the crude oil, under tight formation conditions.

Graphene Quantum Dots Electrochemistry and Development of Ultrasensitive Enzymatic Glucose Sensor

AbstractGraphene quantum dots (GQDs) - zero-dimensional materials - are sheets of a few nanometers in lateral dimension and exhibit quantum confinement and edge site effects where sp2-bonded carbon nanocore surrounded with edged plane functional moieties is promising as advanced electroactive sensing platforms. In this work, GQDs are synthesized by solvothermal and hydrothermal techniques, with optimal size of 5 nm. Their potential in fundamental (direct electron transfer) and applied (enzymatic glucose biosensor) electrochemistry are demonstrated. Glucose oxidase (GOx) immobilized on glassy carbon (GC) electrodes modified with GQDs are investigated by means of cyclic voltammetry, differential pulse voltammetry, and amperometry. Well-defined quasi-reversible redox peaks observed under various electrochemical parameters helped to determine diffusion coefficient (D) and first-order electron transfer rate (kET). The cyclic voltammetry curves showed homogeneous ion transport for GQD with D ranging between 8.45 × 10−9 m2 s−1 and 3 × 10−8 m2 s−1 following GO < rGO < GQD < GQD (with FcMeOH as redox probe) < GOx/rGO < GOx/GO < HRP/GQDs < GOx/GQDs. The developed GOx-GQDs biosensor responds efficiently and linearly to the presence of glucose over concentrations ranging 10 μM and 3 mM with limit of detection 1.35 μM and sensitivity 0.00769 μA μM−1·cm−2 as compared with rGO (0.025 μA μM−1 cm−2, 4.16 μM) and GO (0.064 μA μM−1 cm−2, 4.82 μM) nanosheets. The high performance and stability of GQDs is attributed to sufficiently large surface-to-volume ratio, excellent biocompatibility, abundant hydrophilic edge site density, and partially hydrophobic planar sites that favors GOx adsorption on the electrode surface and versatile architectures to ensure rapid charge transfer and electron/ion conduction (<10 ms). We also carried out similar studies with other enzymatic protein biomolecules on electrode surfaces prepared from GQD precursors for electrochemical comparison, thus opening up potential sensing applications in medicine as well as bio-nanotechnology.

Moisture Sorption and Desorption in Epoxy Composites Reinforced with Triangular and V-Shaped Bars: Determination of Diffusion Coefficient and Effect of Varied Factors

Sorption and desorption of moisture in epoxy composites reinforced with triangular and V-shaped bar fillers were studied. Epoxy was reinforced with vinyl ester bar assemblies fabricated according to 4 varied factors: bar orientation relative to diffusion direction (pointed or base side), bar alignment (parallel or staggered), spacing between bars (1 or 5 mm), and bar cross-sectional shape (triangular or V-shaped). Unlike previous studies, the bar fillers were initially coated with small amount of epoxy resin to improve wetting during fabrication of composites. Moisture uptake and loss of composites during one-side exposure to water vapor (50% relative humidity at 60°C) and hot air (60°C), respectively, were monitored with time. Experimental results show weight change of composites during moisture sorption and desorption varies linearly with square root of exposure time. Diffusion coefficients of composites were determined by assuming the material to be semi-infinite and fitting a mathematical solution to Fick’s second law of diffusion to weight change data. Results show diffusion coefficient of composites during moisture sorption is increased when bars are oriented pointed relative to diffusion direction, aligned parallel, spaced at 1 mm, and has triangular cross-sectional shape. However, during desorption, the diffusion coefficient is increased when base side of bars are exposed and when the bars are aligned staggered. The observed effects of factors on moisture diffusion coefficients of epoxy composites during sorption and desorption are discussed in relation to path length, available diffusion area, and status of epoxy/vinyl ester interphase before and after moisture sorption in composites.

Determination of diffusion coefficient for released nanoparticles from developed gelatin/chitosan bilayered buccal films

This study aims at the mathematical optimization by Box-Behnken statistical design, fabrication by ionic gelation technique and in vitro characterization of insulin nanoparticles containing thiolated N- dimethyl ethyl chitosan (DMEC-Cys) conjugate. Then Optimized insulin nanoparticles were loaded into the buccal film, and in-vitro drug release from films was investigated, and diffusion coefficient was predicted. The optimized nanoparticles were shown to have mean particle size diameter of 148nm, zeta potential of 15.5mV, PdI of 0.26 and AE of 97.56%. Cell viability after incubation with optimized nanoparticles and films were assessed using an MTT biochemical assay. In vitro release study, FTIR and cytotoxicity also indicated that nanoparticles made of this thiolated polymer are suitable candidates for oral insulin delivery.