Diffusion Rate Of Water Molecules Research Articles

Molecular simulation study of the influence of different surfactants on the wetting characteristics of anthracite

The reduction of dust pollution in coal mines is of great importance both for protection of the environment and for the occupational safety and health of coal mine workers. The reduction of dust from anthracite has been a challenge due to its inherent hydrophobicity and high metamorphism. As a result, surfactants are commonly added to water to improve the wettability of coal, thereby improving the dust reduction efficiency of a water spray system. To clarify from a microscopic perspective the effect of different surfactants on the wettability of anthracite, models for the anthracite-surfactant-water system were established, and adsorption configuration, relative concentration distribution, and the diffusion coefficients of water molecules in the systems were thoroughly investigated with molecular simulations. The results showed the directional arrangement of surfactants in the simulation systems after 150 ps of equilibration, resulting in the reduced surface tension of the water-surfactant solution and enhanced wettability of anthracite. Along the (001) normal direction, the relative concentration of sodium dodecylbenzenesulfonate (SDBS) (15.32), the anthracite-water overlapping area, the diffusion rate of water molecules, and the activity (DSDBS = 0.97 × 10-8 m2·s−1) were maximized, indicating the excellent wettability effect of SDBS. The results of the study are of practical significance for improving the wetting effect of anthracite, improving the dust reduction efficiency, and safeguarding the occupational safety and health of personnel.

Simulation of the multiphase molecular effect of polymer flooding oil

Polymers are widely used in the tertiary oil recovery process due to their high stability, light weight and low cost. However, the macroscopic experimental research of polymers is limited by its own hypothetical conditions and cannot obtain good simulation results, which is not enough to reveal the mechanism of polymer flooding. In this paper, combing chemical, computer science and molecular dynamics methods, using non-ionic polyacrylamide, a polymer flooding model is established to simulate the movement of multiphase molecules in the process of polymer flooding from the microscopic level.Studying the diffusion, adsorption and aggregation of multiphase molecules, it was found that the diffusion rate of water molecules and NPAM molecules decreases with the growth of NPAM molecular chains. When NPAM molecules reach the critical concentration of aggregation, the interaction force between NPAM and kaolinite reaches saturation. Shearing can disrupt the length of NPAM molecular chains and accelerate the diffusion of NPAM molecules. The phenomenon of local aggregation of NPAM molecular chains in polymer solution systems occurs. revealing the interaction process of multiphase molecules in the process of polymer flooding, quantifying the diffusion laws of three molecules (polymer, oil and water), and enriching the theoretical system of polymer flooding flow.

Research progress in the evaluation of glymphatic system function by the DTI-ALPS method.

The glymphatic system can remove metabolic wastes from the brain, which plays a significant role in maintaining the homeostasis of the central nervous system. It is an important basis for advanced cognitive functions such as learning and memory. Studies have analyzed the function of glymphatic system by diffusion tensor imaging analysis along the perivascular space (DTI-ALPS) recently. Compared with other invasive examinations that require fluorescent tracer technique or the injection of contrast agents, DTI-ALPS can evaluate the hydromechanics of the glymphatic system via quantifying the diffusion rate of water molecules in different directions, which turns out to be a non-invasive in vivo neuroimaging method. The ALPS-index calculated by the DTI-ALPS method is significantly correlated with the cognitive function in diseases of central nervous system and other system and can reflect the dynamic changes of diseases. In general, ALPS-index is expected to become a novel neuroimaging biomarker for predicting prognosis and clinical effects.

Improving flotation decarbonization efficiency of coal gasification fly ash by mechanically breaking pore: An experimental and molecular dynamics simulation study

The high unburned carbon content of solid waste coal gasification fly ash is the main reason that it cannot be used in the construction material industry, which leads to serious waste of resources and environmental pollution. Currently, decarburization flotation has been a dominating method for coal gasification fly ash resource utilization. However, the flotation process has low efficiency and high reagent consumption because of the rich surface porosity of unburned carbon. Herein, we innovatively developed a mechanical grinding strategy to break the pore distribution on the surface of unburned carbon, significantly reducing the pore size, increasing hydrophobic functional groups and improving the flotation efficiency. The removal rate of unburned carbon is more than 95% in flotation tailings with a mechanical grinding intensity of 120 rpm and grinding time of 30 min. Furthermore, the adsorption of water on porous unburned carbon surface was studied by molecular dynamics simulation for the first time, and the results show that decreasing the particle surface porosity of unburned carbon can accelerate the diffusion rate of water molecules on the unburned carbon surface, improve the wettability of the particle surface and increase the adhesion probability between the unburned carbon particles and bubbles and remarkably improve the its floatability. This work is the first application of mechanically breaking pore to the flotation separation of unburned carbon and ash from coal gasification fly ash and provides valuable inspiration for the design of porous particles flotation, not limited to the separation of gasification fly ash.

Hysteresis Dynamic Modeling and Analysis of Flexible Nano Silver-Polyvinyl Alcohol Humidity Sensor Based on the Microscopic Process and Langmuir-Fick Theory.

In recent years, advances in materials science and manufacturing technologies have facilitated the development of flexible sensors. However, there are still performance gaps between emerging flexible sensors and traditional silicon-based rigid sensors, especially lacking dynamic modeling and optimization analysis for addressing above challenges. This paper describes a hysteresis dynamic modeling method for flexible humidity sensors. Through inkjet printing and coating methods, the polyvinyl alcohol (PVA) sensitive layer and nano silver interdigital electrode are fabricated on flexible polyethylene naphthalate substrates. The performance characterization results show that the sensitivity and maximum hysteresis within the range of 12–98% relative humidity (RH) are −0.02167 MΩ/% RH and 2.7% RH, respectively. The sensor also has outstanding dynamic response ability and stability in a wide range of humidity variation. The hysteresis mechanism of flexible humidity sensors is theoretically analyzed from microscopic hysteresis processes, Langmuir monomolecular adsorption dynamic modeling, and Fick diffusion dynamic modeling. These hysteresis models provide a path for the hysteresis optimization of flexible PVA humidity sensors. Further exploration of the diffusion rate of water molecules and the proportion of PVA in ink represents promising hysteresis optimization directions of flexible humidity sensors based on PVA-sensitive material.

Study on the preparation of coal wastewater slurry from salt/alkali wastewater

Combining experimental research and simulation calculation, the effect of high-concentration salt/alkali wastewater on the preparation of coal wastewater slurry (CWWS) was studied. The research on the slurry-ability of CWWS shows that Na+ in NaCl will be electrically neutralized with the negative charge on the coal, the electrostatic repulsion of particles will decrease, and the viscosity will increase. In the presence of HCO3c, negative charge increases on coal particles, the apparent viscosity decreases by 42 mPa·s compared with the absence of HCO3−. In the CO32− systems, the pH is 8.25. Higher pH indicates that there are more OH−. Because CO32− is easy to combine with water to form a stable structure, and the strong polar effect of OH− is also easy to bind water molecules, forming a stable water molecule layer configuration on the coal, which hinders the adsorption of sodium lignosulfonate (SL), resulting in a decrease in steric hindrance effect, which is not conducive to the dispersion of particles. The molecular dynamics (MD) simulation results confirmed the existence of the neutralization of Na+ and the negative charge on coal in the NaCl system. The adsorption energies (Eadsorption) of each system were negative, indicating that the dispersant was easily adsorbed on the coal. However, in the CO32− system, the absolute value of Eadsorption was lower than that the pure water system, indicating that the presence of CO32− is not conducive to the adsorption of SL. The self-diffusion coefficient(D) of Na2CO3 system is lower than that of coal/water/SL system, NaCl system, and NaHCO3 system. It shows that the presence of CO32− can significantly reduce the migration rate of water molecules and is easy to bind water molecules. The presence of HCO3− is also easy to bind water molecules, but it is weaker than CO32−. The migration and diffusion rate of water molecules in the saline-alkali mixed system decrease. This may be mainly affected by CO32−, which easily binds water molecules on the coal surface and hinders the adsorption of SL.

Study of sodium lignosulfonate prepare low-rank coal-water slurry: Experiments and simulations

Abstract The effect of sodium lignosulfonate (SL) as additive on the preparation of low-rank coal-water slurry (LCWS) was studied by experiments and molecular dynamics (MD) simulations. The experimental results show that the appropriate amount of additives is beneficial to reduce the viscosity of LCWS and increase the slurry concentration. Adsorption isotherm studies showed that SL conforms to single-layer adsorption on the coal surface, and ∆ Gads0 was negative, proving that the reaction was spontaneous. Zeta potential measurements showed that SL increased the negative charge on coal. FTIR scanning and XPS wide-range scanning were performed on the coal before and after adsorption, and it was found that the content of oxygen functional groups on coal increased after adsorption. Simulation results show that when a large number of SL molecules exist in the solution, some SL molecules will bind to hydrophobic hydrocarbon groups on coal. The rest of the SL molecules, their hydrophobic alkyl tails, come into contact with each other and aggregate in solution. The agglomeration of SL molecules and the surface of coal with static electricity will also produce electrostatic interaction, which is conducive to the even dispersion of coal particles. The results of mean square displacement (MSD) and self-diffusion coefficient (D) show that the addition of SL reduces the diffusion rate of water molecules. Simulation results correspond to experimental results, indicating that MD simulation is accurate and feasible.

Mechanical, low-velocity impact, and hydrothermal aging properties of flax/carbon hybrid composite plates

A hybrid of flax and carbon fibers was considered as an effective way to enhance the mechanical and hydrothermal resistance of flax-reinforced polymer composites. In this study, hybrid composites based on three layers of cross-ply flax fabrics, two layers of unidirectional carbon fabrics, and an epoxy resin were investigated in terms of the tensile, three-point bending, impact, and water absorption properties. The flax fabric reinforcement of the hybrid composites contributed to an improvement in the toughness, whereas the carbon fabric contributed to an improvement in their hydrothermal resistance and overall strength and stiffness. The hybrid composites with carbon fibers on the surface (CFFFC) exhibited brittle failure in the tensile test, whereas those with alternating layers (FCFCF) exhibited greater plastic deformation. In addition, the failure strain of the CFFFC samples showed a negative hybrid effect, whereas that of the FCFCF samples improved 63.5% compared with that of carbon-fiber-reinforced polymer composites. A positive hybrid effect on the impact performance of hybrid reinforced epoxy composites containing the unidirectional carbon fabric and cross-ply flax fabric was observed. At 40 °C and 80% relative humidity, the diffusion rate of water molecules in the FCFCF samples was 16 times that in the CFFFC samples.

Study on the hygrothermal aging behavior and diffusion mechanism of Ti/CF/PMR polyimide composite laminates

A series of hygrothermal aging experiments were performed on Ti/CF/PMR polyimide (TCPP) composite laminates in this work in order to verify the moisture diffusion characteristics and diffusion mechanism of the laminate. The specimens were subjected to various hygrothermal aging parameters, specifically 70 °C/95RH%, 85 °C/75RH%, 85 °C/85RH% and 90 °C/95RH%. The results illustrate that the temperature affected the diffusion rate of water molecules in the composite laminates, and the relative humidity determined the saturated moisture absorption rate. For the orthogonally laminated TCPP composite laminates, two equations have been obtained to predict the saturated moisture absorption and diffusion rate of water molecules of the prepreg layer. Additionally, the moisture absorption as a function of time has been expressed for the prepreg layer.

Pitfalls in Diffusion-Weighted and Diffusion Tensor Imaging of the Pediatric Brain.

AbstractDiffusion-weighted imaging (DWI) and diffusion tensor imaging (DTI) are advanced magnetic resonance imaging (MRI) techniques that are based on differences in the diffusion rate of water molecules in brain tissue. DWI and DTI are widely used in pediatric neuroradiology to evaluate a wide spectrum of brain diseases. The interpretation of DWI and DTI images requires a basic knowledge of the underlying physics to detect potential pitfalls and avoid misinterpretation. Several DWI pitfalls are related to the dependency of DWI images not only on the diffusivity of water molecules, but also on various additional MRI phenomena such as the T1- and T2- relaxation characteristics and MRI-related artifacts. In addition, knowledge about the age of the child and interval between the onset of injury and acquisition of DWI/DTI images is important. Finally, qualitative evaluation (“eye-balling”) maybe misleading, and the application of quantitative measurements of DTI scalars may avoid misdiagnosis.

Boron nitride nanotube as a delivery system for platinum drugs: Drug encapsulation and diffusion coefficient prediction

Molecular dynamics (MD) simulation has been applied to investigate a drug delivery system based on boron nitride nanotubes, particularly the delivery of platinum-based anticancer drugs. For this propose, the behavior of carboplatin drugs inserted in boron nitride nanotubes (BNNT) as a carrier was studied. The diffusion rate of water molecules and carboplatin was investigated inside functionalized and pristine boron nitride nanotubes. The penetration rate of water and drug in functionalized BNNT was higher than that in pristine BNNT due to favorable water-mediated hydrogen bonding in hydroxyl edge–functionalized BNNT. Additionally, the encapsulation of multiple carboplatin drugs inside functionalized boron nitride nanotubes with one to five drug molecules confined inside the nanotube cavity was examined. At high drug loading, the hydrogen bond formation between adjacent drugs and the non-bonded van der Waals interaction between carboplatin and functionalized BNNT inner surface were found to be influential in drug displacement within the functionalized BNNT cavity for higher drug-loading capacity.

Preparation and Characterization of Poly(lactic Acid)-based Composite Reinforced with Oil Palm Empty Fruit Bunch Fiber and Nanosilica

The properties of poly(lactic acid) (PLA) bio-composite films reinforced with oil palm empty fruit bunch (OPEFB) fiber and nanosilica were studied in this work. The composite films were prepared via the solvent casting method. The composites were characterized via Fourier transform infrared spectroscopy (FTIR), UV-visible spectroscopy, field-emission scanning electron microscopy (FESEM), tensile testing, and X-ray diffraction (XRD). Ultraviolet visible spectroscopy results revealed that the PLA-based composites and neat PLA had similar light transmittances of approximately 89%. The FTIR and FESEM results showed that OPEFB fibers and nanosilica were embedded into the PLA matrix. The tensile strength of the composites with addition of nanosilica increased with an increasing fiber load content. The XRD analysis showed that the addition of organic or inorganic silica reduced the crystallinity of the composites. The water vapor permeability test results indicated that the inorganic silica decreased the diffusion rate of water molecules through the polymer film. The OPEFB-reinforced PLA blend with additional organic silica exhibited a higher thermal stability than the composites reinforced with inorganic silica.

Assessment of the apparent diffusion coefficient (ADC) of normal breast tissue during the menstrual cycle at 3T using image segmentation

Diffusion weighted imaging (DWI) is quantitative MRI technique that generates an image contrast based on the intrinsic random motion properties of water molecules within tissue, known as Brownian motion. It is able to detect any physiological abnormality at the cellular level and the assessment of the change can be visually (qualitative) assessed by observing the alteration in signal intensity (SI) and also can be quantitatively assessed by calculating the apparent diffusion coefficient (ADC) value which reflects the diffusion rate of water molecules [1]. Based on histological studies the menstrual cycle is divided into four phases (weeks): menstrual (week 1), follicular (week 2), ovulation (week 3), and luteal (week 4). The morphologic changes occur in stromal and epithelial tissues due to the rise and fall of oestrogen and progesterone levels and were first described by Rosenberg [2]. The mammary epithelium changes from small cuboidal cells in the first half of the cycle to tall, columnar, well differentiated cells in the second half of the cycle. The follicular phase is characterized by the gradual increase in oestrogen levels which peak at ovulation. During this phase the glandular lumen is poorly defined and contains minimal secretions. The intralobular tissue is characterized by dense stroma and more collagenous tissue with less cell density. However, during the luteal phase the secretion of progesterone hormone increases and peaks leading to greater proliferative and mitotic activity of the mammary epithelium resulting in enlarged lobules which become more rounded with active secretion into the lumen. The intralobular stroma becomes distinctly loose due to the accumulation of oedema [3]. Several MRI studies have been performed demonstrating that the vascularity of the breast parenchymal tissue changes during

Environmental-Friendly Soy Protein Isolate/Poly (Vinyl Alcohol) Blend Packaging Films: Water Vapor Permeability

The aim of the present work was to investigate the moisture sensitivity of soy protein isolate (SPI) films blending with poly (vinyl alcohol) (PVA) plasticized by glycerol. Water vapor permeability (WVP) was measured based on the contents of PVA and glycerol in films. WVP values of various SPI/PVA films with/without glycerol were in the range of 8.25 and 10.9 g mm/m2 h kPa. The results showed that WVP values decreased with the increasing content of PVA. Moreover, XRD tests confirmed that the glycerol would insert into the macromolecular blending structure and destroy the crystalline of blends, and the crosslinkage between glycerol molecules and SPI reduced the interstitial spaces in protein matrix, thus allowing for decreasing diffusion rate of water molecules through the films.

Flow characteristics and reaction properties of carbon dioxide in microtubules and porous media

Carbon dioxide reacts with porous media while flowing through them enhancing their permeability. Its flow behavior as well as the permeability enhancement effects were studied in synthetic cores, natural cores and microtubes with an inner diameter of 5 μm. The results show that the permeability of H2O-saturated cores (containing carbonate ingredients) was enhanced by increasing the injection volume of a CO2-H2O solution. This enhancement is attributable to carbon dioxide’s corrosion, which is justified by SEM scanning. The same phenomenon occurs with a CO2-H2O solution in microtubes, but for a different reason. The gas flow velocity of carbon dioxide in microtubes was approximately 100% faster than that of nitrogen because of the scale and the squeezing effects. Carbon dioxide molecules dissolved in water accelerate the diffusion rate of water molecules within the boundary layer, which in turn diminishes the thickness of the water film and enlarges the effective pore size. This flow behavior facilitates the injection of carbon dioxide into low-permeability reservoirs for oil-displacement and formation energy buildup purposes. This behavior also increases the potential for carbon dioxide channeling or release from the formation.

Imagerie par résonance magnétique de diffusion de l'encéphale chez l'adulte : technique, résultats normaux et pathologiques

By probing microscopic molecular motions, diffusion-weighted imaging (DWI) is the only method available today that provides noninvasively information on molecular displacements over distances comparable to cell dimensions. Since it measures a parameter different from those assessed by conventional MRI, DWI represents a new imaging technique that goes beyond depiction of neuroanatomy and evaluates function and physiopathology. Image contrast is related to differences in the diffusion rate of water molecules rather than to changes in total tissue water. DWI has proven its high sensitivity in early detection of acute infarction; it is reliable in differentiating acute stroke from other diseases that mimic acute stroke in clinical terms and on conventional MR images. By differentiating lesions with decreased diffusion from those with increased diffusion, DWI is useful in the evaluation of a wide variety of other disease processes including neoplasms, demyelization, traumatic brain injury, intracranial infections. In particular, DWI can distinguish between epidermoid and arachnoid cysts and provides key information for the diagnosis of cerebral abscess. In some clinical situations, DWI data have a prognostic value.

1.8 ka old glass from the Roman ship Julia Felix: glass–water oxygen isotope exchange

A set of glass samples from the sunken Roman ship Julia Felix, off the town of Grado (Gorizia, Italy) around the second half of the 2nd century AD has been studied along with other glass samples from almost coeval levels of archaeological excavations in the cities of Vicenza (northern Italy) and Pozzuoli (Naples, southern Italy) and in the town of Grado (7th–9th century AD). The glass samples are fairly homogeneous in their chemical composition with typical silicic–sodic–calcic compositions. Superficial lamellar layers of various thickness (from about 200 μm to less than thousand μm) were formed by the glass–water alteration process. The oxygen isotopic composition of the alteration patinae was measured along with that of the apparently unaltered internal section of glass. The oxygen isotopic composition of the Northern Adriatic seawater is known from previous studies along with the mean oxygen isotopic composition of local precipitations at Vicenza, Pozzuoli and Grado. The mean annual temperatures at the sea bottom are also known from previous studies. The knowledge of the age of the ship and of these variables allows the calculation of the diffusion rate of water molecules through the glass and the glass/water fractionation factor at low temperature. The calculated α-values for the ship glasses are very close to one another and consistent among different samples. One of the glass samples from archaeological excavations (Grado) shows an α-value smaller than those calculated for the ship samples. This suggests partial isotope exchange probably related to the reduced exchange time with water (∼50%) and, perhaps, to the small amount of water available to this sample. From the results obtained, it is possible to conclude that glass–water oxygen isotope exchange occurs even at relatively low temperatures, isotopic equilibrium being reached in less than 1.8 ka when large amounts of water are available.

Dissolution mechanism and release kinetics of phosphate controlled release glasses in aqueous medium

Leach test of a phosphate controlled release glass (CRG) were conducted in aqueous medium under different conditions. Results show that the phosphate CRG dissolves congruently in deionized water. Its dissolution rate is dependent with the solution pH, temperature and concentrations of phosphate ions and calcium ions in the medium, but independent with the stirring speed of the solution. Analysis leads to a conclusion that the dissolution of phosphate glass is a reaction-controlled process. Discussions on the dissolution mechanisms show that the nature of the reaction in the hydrated layer is the dissociation of Na + ions from the phosphate chains under the attack of the penetrating water molecules. The velocity of formation and development of hydrated layer depends on the diffusion rate of water molecules inside glass. The dissolution is realized by the breakage of P–O–P bonds in the phosphate network within the hydrated layer. The chelating ability of polyphosphate with divalent cations play an important role in the dissolution process of phosphate CRGs and was found responsible for the accelerated or decelerated dissolution of the CRG in sodium hexametaphosphate (SHMP) or CaCl 2 solutions, respectively.

Wall and aerosol condensation during cooled laminar tube flows

The equations for heat and mass transfer in laminar flow are presented and their solutions are considered in the limit of low vapor density and constant thermodynamic properties. Simple ways of determining the maximum and minimum possible wall condensation are discussed. Numerical calculations between these limits are performed by orthogonal collocation. For dibutyl phthalate vapor in air, latent heat release is negligible and most of the vapor condenses das aerosol. New results are presented for water vapor, including the effects of latent heat. Water aerosol growth is inhibited due to latent heat release and most of the vapor condenses on the wall. Also, water droplets near the tube axis may evaporate, due to the large diffusion rate of water molecules to the wall.

Tritium exchange experiments on thin microporous silica layers

The tritium-hydrogen exchange and the tritium distribution in tritium-labelled thin microporous silica layers was studied with a washing and etching technique. The tritium distribution was found to be homogeneous along the whole thickness of the layer. The exchange process can be resolved in three diffusion processes which can be related, in order of decreasing rate, to tritium: (i) in the physisorbed water molecules in the micropores; (ii) in the silanol groups in the micropores; and (iii) in bulk intra-skeletal silanol groups, respectively, in agreement with the description of the microporous silica layer given by Grigorovich et al. The diffusion rate of the water molecules resembles the diffusion rate of water molecules in ice I. The diffusion coefficient of the hydrogen in the micropore silanol groups (5 × 10 −17 m 2 s −1) is much higher than the self-diffusion coefficient D H ≈ 10 −21 m 2 s −1, calculated from the previously studied sodium-hydrogen exchange processes in the silica film using the interdiffusion coefficient according to Doremus. However, the former diffusion coefficient is compatible with the diffusion coefficient of the “free” hydrogen ions, calculated from the sodium-hydrogen exchange process using an interdiffusion coefficient according to Helfferich by which the dissociation of the silanol groups in the micropores is taken into account, if the dissociation constant is about 10 −9.