Diffusion Process Of Water Molecules Research Articles

Moisture absorption characterization of carbon fiber‐reinforced polymer using Fickian and non‐Fickian models

AbstractThree classic moisture absorption models including the Fickian model, the Langmuir and the time‐variable diffusion model were adopted to describe the absorption behavior of carbon fiber‐reinforced polymer (CFRP) laminates in this work. A new non‐Fickian model based on the two‐phase absorption rule was proposed by introducing the equivalent absorption time into the Langmuir model. Experiments of accelerated moisture absorption were conducted for CFRP laminates with different lay‐ups under three temperatures. Moisture uptaking performance of the CFRP laminates was discussed. Preliminary data analysis of the moisture absorption content showed the existence of non‐Fickian diffusion behavior. Four numerical models were implemented into Matlab by combining the Gauss‐Newton algorithm with minimum mean square error. Effects of the environment temperature and the lay‐ups of the laminates on the diffusion process of water molecules in CFRP. The results demonstrated that the modified time‐variable Langmuir model shows the best fitting performance. The diffusion coefficient and equilibrium moisture uptake increased with the environment temperature. Water diffusion coefficients in monotonous ply‐structure is larger than that in multi‐angle plys.

Roles of aqueous additives in the mass transfer process of water molecules in water/oil/water double emulsion droplets

Finding suitable aqueous additives to inhibit the mass transfer of water molecules in double emulsion droplets is beneficial for improving the surface quality of polymer shells. In this work, fluorobenzene/aqueous systems with polyvinyl alcohol (PVA) molecules and electrolyte ions were constructed by molecular dynamics simulation, which are typical water/oil (W/O) systems in actual fabrication processes of polymer shells. The interfacial mass transfer coefficients and equilibrium water solubility in fluorobenzene of various W/O systems were calculated by fitting the dissolution curves with a classical mass transfer model. The effects of polyvinyl alcohol additives on the diffusion process of water molecules at the fluorobenzene/water interface were investigated from the perspectives of thermodynamics and microscopic interface morphology. Furthermore, to avoid the inner surface defects of polymer shells caused by electrolyte ions osmosis, 1,3-butanediol molecules were proposed to replace ions as aqueous solutes, which also inhibited the diffusion of water molecules to fluorobenzene membrane.

A Molecular Interpretation of the Dynamics of Diffusive Mass Transport of Water within a Glassy Polyetherimide.

The diffusion process of water molecules within a polyetherimide (PEI) glassy matrix has been analyzed by combining the experimental analysis of water sorption kinetics performed by FTIR spectroscopy with theoretical information gathered from Molecular Dynamics simulations and with the expression of water chemical potential provided by a non-equilibrium lattice fluid model able to describe the thermodynamics of glassy polymers. This approach allowed us to construct a convincing description of the diffusion mechanism of water in PEI providing molecular details of the process related to the effects of the cross- and self-hydrogen bonding established in the system on the dynamics of water mass transport.

Interfacial mass transfer of water for fluorobenzene/aqueous solution system in double emulsion

Understanding the dissolution and diffusion process of water molecules across the oil/water interface is helpful to fabricate polymer shells with high surface quality. In this work, microscopic fluorobenzene/water, fluorobenzene/NaCl(aq) and fluorobenzene/1,3-butanediol(aq) systems are constructed by molecular simulation. The solubility of water in fluorobenzene and interfacial diffusion resistances is calculated by fitting the simulated dissolving curves to a one-dimensional surface evaporation continuum model. The equilibrium solubility, interfacial diffusion resistances and component diffusivities are calculated for the oil/water systems. The simulated water solubility and diffusivity in fluorobenzene at 320 K are 305 ppm and (8.38 ± 0.29) × 10−9 m2/s, respectively. The density distribution near the oil/water interface is statistical averaged and the solution microstructures are analyzed. Both the ions and alcohol molecules added in the aqueous phase can slow down the water dissolving process, by reducing the equilibrium solubility and interfacial mass transfer rate of water in fluorobenzene. Applying the properties provided by microscopic simulations to the macroscopic mass transfer model, the characteristic time t∞ (0.05–1.34 s) when the dissolved water mass reaches 95% of the equilibrium solubility is calculated for fluorobenzene membranes with a width range of 50–200 μm, which provides a time reference for double emulsions treatment process in polymer shell fabrication.

Diffusion-weighted breast imaging.

Magnetic resonance imaging (MRI) of the breast represents one of the most sensitive imaging modalities in breast cancer detection. Diffusion-weighted imaging (DWI) is asequence variation introduced as acomplementary MRI technique that relies on mapping the diffusion process of water molecules thereby providing additional information about the underlying tissue. Since water diffusion is more restricted in most malignant tumors than in benign ones owing to the higher cellularity of the rapidly proliferating neoplasia, DWI has the potential to contribute to the identification and characterization of suspicious breast lesions. Thus, DWI might increase the diagnostic accuracy of breast MRI and its clinical value. Future applications including optimized DWI sequences, technical developments in MR devices, and the application of radiomics/artificial intelligence algorithms may expand the potential of DWI in breast imaging beyond its current supplementary role.

Water-selective permeation in hybrid membrane incorporating multi-functional hollow ZIF-8 nanospheres

Incorporating metal-organic frameworks (MOFs) into polymer to fabricate hybrid membranes is an effective approach of breaking the trade-off between permeability and selectivity. In this study, hollow zeolitic imidazolate framework-8 (HZIF-8) nanospheres were prepared and blended into sodium alginate (SA) matrix to fabricate water-selective hybrid membrane, which intensify the diffusion process of water molecules dramatically owing to their well-designed hierarchical structures. The micropores on HZIF-8 nanosphere shell have a molecular sieving effect, which enhances diffusion selectivity of water molecules. The hollow structure of HZIF-8 nanospheres ensures the rapid diffusion of water molecules, thus elevating the permeation flux and separation factor simultaneously. Besides, the intervention effects of HZIF-8 nanospheres on the SA chain packing also contribute to the enhancement of permeation flux and separation factor by rendering the membrane more free volume cavities and suitable free volume cavity size for ethanol/water separation. When utilized to separate 90 wt% ethanol aqueous solution at 76 °C, the hybrid membrane containing 6 wt% HZIF-8 displays the highest separation performance with permeation flux of 2485 g/m2 h and separation factor of 1884, much superior to those for pure SA membrane and the hybrid membranes incorporating zeolitic imidazolate framework-8 (ZIF-8) nanocrystals. Desirable long-term stability of the hybrid membranes was also acquired.

High sensitivity and fast response graphene oxide capacitive humidity sensor with computer-aided design

A COMSOL model of interdigital capacitive humidity sensor based on graphene oxide (GO) as sensing material is presented. The diffusion process of water molecules and the effects on the capacitance value are demonstrated in theory. The capacitance value of the model is shown in simulation under different relative humidity, and also the influences of structural parameters are summarized, which can be used to construct electrode structure for increasing the sensitivity of humidity sensor. Furthermore, response time of the module is tested through dynamic process simulations, the results show more advanced performance compared with another module. The process of argumentation suggests that this model can also be used for the optimization of other gases capacitive sensors.

TU‐C‐12A‐06: Computerized Analysis of Diffusion‐Weighted Images in Breast Cancer Diagnosis

Purpose:Diffusion‐weighted imaging (DWI) for breast MRI is a non‐invasive technique which maps the diffusion process of water molecules, with the use of Brownian motion, in biological tissues, yielding apparent diffusion coefficients (ADC). Quantitative image analyses of the resulting images can yield information about the surrounding tissues in vivo. In this study, we investigated computerized image analyses of DWI images, including automated lesion segmentation, calculation of ADC values, and assessment of tumor heterogeneity, on a dataset of malignant and benign breast lesions.Method and Database:The IRB‐approved, retrospectively collected dataset included 46 breast lesions ‐‐ 36 malignant and 10 benign. The DW images had been acquired during clinical breast MRI on a high‐field 1.5 T echo‐planar system using five b values [b = 0, 500, 1000, 1500, and 2000 s/mm2]. Seed‐point‐initiated 3D Gaussian‐based lesion segmentation was conducted to yield the lesion margins, and within the margin and after b‐value fitting, ADC values were calculated. Average ADC values and various measures of heterogeneity were calculated for benign and malignant lesions.Results:Our findings showed that malignant lesions tended, as expected, to have lower ADC values relative to benign lesions with average ADC values for benign and malignant lesions being 1.70 +/− 0.50 × 10(−3) and 1.07 +/− 0.37 × 10(−3), respectively. In addition, malignant lesions showed higher heterogeneity. In the task of distinguishing between benign and malignant lesions, ROC analysis, from histogram analysis, yielded AUC values of 0.86 +/− 0.07 and 0.88 +/− 0.06 for average ADC values and standard deviation of ADC values, respectively.Conclusion:DWI exhibits potential for differentiating between benign and malignant lesions, and inclusion of computerized quantitative image analysis methods allow for more objectives and efficient calculations of the ADC values and their variations, for potential use in decision making.M. L. Giger is a stockholder in R2 Technology/Hologic, is a shareholder/investor in Quantitative Insights, Qview Medical,receives royalties from Hologic, GE Medical Systems, MEDIAN Technologies, Riverain Medical, Mitsubishi and Toshiba.

Bessel Fourier Orientation Reconstruction (BFOR): An analytical diffusion propagator reconstruction for hybrid diffusion imaging and computation of q-space indices

The ensemble average propagator (EAP) describes the 3D average diffusion process of water molecules, capturing both its radial and angular contents. The EAP can thus provide richer information about complex tissue microstructure properties than the orientation distribution function (ODF), an angular feature of the EAP. Recently, several analytical EAP reconstruction schemes for multiple q-shell acquisitions have been proposed, such as diffusion propagator imaging (DPI) and spherical polar Fourier imaging (SPFI). In this study, a new analytical EAP reconstruction method is proposed, called Bessel Fourier Orientation Reconstruction (BFOR), whose solution is based on heat equation estimation of the diffusion signal for each shell acquisition, and is validated on both synthetic and real datasets. A significant portion of the paper is dedicated to comparing BFOR, SPFI, and DPI using hybrid, non-Cartesian sampling for multiple b-value acquisitions. Ways to mitigate the effects of Gibbs ringing on EAP reconstruction are also explored. In addition to analytical EAP reconstruction, the aforementioned modeling bases can be used to obtain rotationally invariant q-space indices of potential clinical value, an avenue which has not yet been thoroughly explored. Three such measures are computed: zero-displacement probability (Po), mean squared displacement (MSD), and generalized fractional anisotropy (GFA).

Multiple q-shell diffusion propagator imaging

Many recent high angular resolution diffusion imaging (HARDI) reconstruction techniques have been introduced to infer an orientation distribution function (ODF) of the underlying tissue structure. These methods are more often based on a single-shell (one b-value) acquisition and can only recover angular structure information contained in the ensemble average propagator (EAP) describing the three-dimensional (3D) average diffusion process of water molecules. The EAP can thus provide richer information about complex tissue microstructure properties than the ODF by also considering the radial part of the diffusion signal. In this paper, we present a novel technique for analytical EAP reconstruction from multiple q-shell acquisitions. The solution is based on a Laplace equation by part estimation between the diffusion signal for each shell acquisition. This simplifies greatly the Fourier integral relating diffusion signal and EAP, which leads to an analytical, linear and compact EAP reconstruction. An important part of the paper is dedicated to validate the diffusion signal estimation and EAP reconstruction on real datasets from ex vivo phantoms. We also illustrate multiple q-shell diffusion propagator imaging (mq-DPI) on a real in vivo human brain and perform a qualitative comparison against state-of-the-art diffusion spectrum imaging (DSI) on the same subject. mq-DPI is shown to reconstruct robust EAP from only several different b-value shells and less diffusion measurements than DSI. This opens interesting perspectives for new q-space sampling schemes and tissue microstructure investigation.

Optimization of in vivo high-resolution DTI of non-human primates on a 3T human scanner

Magnetic resonance (MR) diffusion tensor imaging (DTI) has emerged as a unique technique to reveal small anatomical structures of brain by characterizing the diffusion process of water molecules within an image voxel. Combined with fiber tractography techniques, DTI can be further used to reveal white matter fibers and connectivity in the brain non-invasively. The non-human primate brain study provides important supplemental means for human brain exploration since the two species share close anatomical and functional similarities. There is therefore increasing interest in in vivo non-human primate DTI studies. However, several technical challenges need to be addressed to perform non-human primate brain DTI and fiber tractography. We have established an imaging protocol together with a post-acquisition procedure for high-resolution in vivo non-human primate DTI studies using a 3T human clinical scanner. Data acquired with this procedure is appropriate for accurate diffusion tensor quantification and fiber tractography, and is accessible within an acceptable scan time. We investigated in detail the effects of spatial resolution and SNR on diffusion tensor-derived quantities and fiber tractography. Our results should be of general utility for implementation of in vivo non-human primate DTI studies.

Variational inference of the fiber orientation density using diffusion MR imaging

Diffusion MR imaging has enabled the in vivo exploration of the connectional architecture in human brain. This method particularly reveals the complex system of long-range nerve fibers that integrate the functionally distinct areas of the cerebral cortex. Since the fibers are not directly observed but the diffusion process of water molecules in the underlying material, a forward model is established that maps the microgeometry of nervous tissue onto the diffusion-weighted signals. This article proposes the spherical deconvolution of the fiber orientation density in a reproducing kernel Hilbert space, thereby generalizing previous approaches that perform a truncated Fourier analysis on the sphere. The specified inverse problem is solved within a smoothing spline framework which preserves the characteristic properties of a density function, namely its normalization and non-negativity. A Gaussian process model allows the specification of confidence bands for the estimated fiber orientation density and the rigorous selection of the hyperparameters, here the high-frequency content in the density function and the noise variance of the MR observations. In addition, we weaken the constant diffusivity assumption frequently made in the spherical convolution methodology. The novel approach, which uncovers the fiber orientation field of white matter, is demonstrated with diffusion-weighted data sets featuring high angular resolution.

Quasielastic neutron scattering study of dynamics of CaCl2 aqueous solution confined in Vycor glass

Quasielastic neutron scattering was used to probe the diffusion of water molecules in 2.3 molal CaCl(2) solution confined in 100% hydrated Vycor glass in the temperature range of 220 to 260 K. We observed a gradual transition from the restricted diffusion regime at lower temperatures to unrestricted diffusion regime at higher temperatures. The diffusion parameters were compared with the data on pure water confined in Vycor available in the literature. We found that the effect of dissolved ions onto the diffusion dynamics of the water molecules in the solution was amplified by confinement by at least an order of magnitude compared to bulk form, even though the dissolved ions were found to have little effect on the spatial characteristics of the restricted diffusion process of water molecules. At 260 K, the local diffusion coefficient of water molecules in the H(2)O-CaCl(2) confined in Vycor was only 6% of the value reported for pure water confined in Vycor.

Molecular Interactions in and Transport Properties of Densely Cross-Linked Networks: A Time-Resolved FT-IR Spectroscopy Investigation of the Epoxy/H2O System

Transport of water in an epoxy network with high cross-link density was investigated at several water vapor activities by time-resolved FT-IR spectroscopy and gravimetric measurements. The analysis of the infrared spectra provided information about the molecular interactions occurring in the system. In particular, several interaction complexes were identified and their structures were proposed. An estimate was made of the concentration of the various water species present in the system, based on the knowledge of the respective molar absorptivities. An excellent agreement between the spectroscopic and gravimetric determinations of sorbed water was found throughout. The evolution of the different water species was monitored by resolving the complex profile of the water spectrum in the νOH frequency range. This information, coupled with the results of the gravimetric analysis, was used to evaluate the effect of polymer/penetrant H-bonding interactions on the diffusion process of water molecules. Transport of the different water species was found to follow a Fickian behavior characterized by an effective diffusion coefficient which increases with total water concentration.

Brain Diffusion Tensor MR Imaging

The development of MR imaging techniques during the past decade has enabled researchers to use MR imaging as a noninvasive tool for evaluating structural and physiologic states in biologic tissues by measuring the diffusion process of water molecules. More recently, diffusion tensor MR imaging (DTI) technique based on the dependency of molecular diffusion on the orientation of white matter fiber tracts has been used to analyze the trajectory, shape, fiber structure, location, topology and connectivity of neuronal fiber pathways in living humans. Numerous efforts have been made by MR physicists, brain scientists, and medical doctors to advance MR techniques and computer-based algorithms which result in more accurate quantification of diffusion tensor and the generation of white matter fiber tract maps and to determine the pathophysiology of brain disease by DTI and useful clinical applications of DTI. In this article, we describe the tensor theory used to characterize molecular diffusion in white matter and a process of measuring tensor elements using diffusionsensitive MR images to fiber mapping. We then provide review of current literature and some clinical examples that have been published and are on-going.

Dynamic Process of Water Sorption in a Thermoplastic Modified Epoxy Resin System

In the present work, dynamic water sorption processes in a series of poly(ether imide) (PEI) modified diglycidyl ether bisphenol A/(4,4‘-diaminodiphenyl)sulfone (DGEBA/DDS) systems were investigated. The clear picture of the existing state and the diffusion process of water molecules in the blends was first elucidated by two-dimensional (2D) correlation analysis (based on attenuated total reflection Fourier transfer infrared (ATR-FTIR) measurement), and the novel technique used here could be the most effective as well as convenient way to perform the dynamic analysis on such investigations. Furthermore, by means of scanning electron microscopy (SEM), the delicate relationship between dynamic water sorption behavior and the morphology resulting from phase separation was also discussed. Two states of water as free/bound water were found in the systems, the diffusion sequence of which suggested not only composite-dependence but also morphology-dependence.

Two-dimensional infrared correlation spectroscopy as a probe of sequential events in the diffusion process of water in poly(ε-caprolactone)

In this study, the diffusion process of water molecules in poly(ε-caprolactone) (PCL) has been investigated using in-situ attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy. In our system, the original broad water OH bands in 1D IR spectra can be effectively differentiated into four bands, located at 3641, 3593, 3410, and 3203 cm−1, respectively, using 2D correlation analysis. The bands at 3641 cm−1 (antisymmetric) and 3593 cm−1 (symmetric) are assigned to the OH stretching vibration of water partially hydrogen bonded with hydrophilic carbonyl group (C=O) of PCL, while the other band pair at 3410 cm−1 (antisymmetric) and 3203 cm−1 (symmetric) could be attributed to the stretching vibration of water fully hydrogen bonded with another water molecule. According to the result of the asynchronous correlation, it was concluded that the water molecules at first diffuse into free volume (microvoids) or are molecularly dispersed into the PCL matrix and then form hydrogen bond with the C=O group of the polymer during the process of water diffusion. In addition, the diffusion coefficient was estimated using nonlinear curve fitting of OH band areas in the range of 3800–3000 cm−1.

雪の結晶成長の律速過程の定量的評価

Growth of snow crystals, i. e. growth of ice crystals from vapor is considered to occur by the following three processes: (1) a surface kinetic process for incorporating water molecules into the crystal lattice, (2) a diffusion process of water molecules in air towards the crystal surface, (3) a heat conduction process of the latent heat of sublimation. The resistance of each process is not constant, but depends on growth conditions such as supersaturation, the diffusion constant of water molecules in air, and also on crystal size. The purpose of the present sudy is the quantitative investigation of the role of each process as a rate determining process, and a discussion of the dependence on crystal size of the growth rate in the case of two-dimensional nucleation growth and in the case of spiral growth under various growth conditions. The results are interpreted from the viewpoint of the change of resistances of individual processes with increasing crystal size.

氷結晶の気相成長の律速過程

Growth of ice crystals from the vapour phase generally occurs in three processes : volume diffusion process of water molecules, surface kinetic process characterized by the dependence on surface supersaturation of the kinetic coefficient and conduction process of the latent heat of sublimation. General expression for the growth rate of ice crystal is derived by taking into account these processes. This expression uses the supersaturation at infinite distance from the crystal surface to describe the macroscopic driving force for the growth and the sum of resistances for the individual processes. By estimating the values of the resistances, we can investigate the role of each process as rate determining process under the given growth conditions specified by temperature, supersaturation, crystal size, air pressure and so on. We also discuss the supersaturation determined by temperature and pressure of water vapour at the crystal surface under various growth conditions.

Diffusion‐controlled mechanical properties of polyvinyl alcohol and polyvinyl formals

AbstractThe elongation of polyvinyl alcohol and of formalized polyvinyl alcohol films under constant load for a wide range of conditions of temperature and humidity seems to be affected predominantly by the diffusion of water molecules into these polymeric films, as these films have many water‐sensitive bonds. In order to obtain a perspective of the diffusion mechanism of water molecules into these polymer films, the theoretical analysis of creep curves is here worked out. Since the diffusion is a time‐dependent, non‐Fickian process, the time dependence of the diffusion coefficient is considered into our theoretical treatment. It is also assumed that the elongation is caused only by the breaking of hydrogen bonds due to the absorption of water molecules in amorphous regions of the polymer film.To evaluate theoretical equations for the creep curves in accordance with a simple Voigt model, the parameter α for the rate of diffusion is conveniently substituted for by K, the parameter for the rate of elongation. Experiments were performed at temperatures from 20 to 50°C. at 60% R. H., and also at different relative humidities ranging from 40 to 80% at a constant temperature of 30°C. A series of creep curves for PVA and PVF, the latter having a degree of formal substitution ranging from 6% to 42.5% were obtained.In analyzing the observed creep curves by the present theoretical treatment, we can easily compute the values of K through application of the condition for the characteristic inflection point of each curve, i.e., d2γ/dt2 = 0. By use of the values of K thus obtained and by application of the theory of absolute reaction rates, the activation energy and entropy for the diffusion process of water molecules are duly determined. The values thus obtained are also compared with those calculated by Hauser and McLaren. The activation energy and entropy are highest and lowest, respectively for PVF (6%); this is made adequately explicable by the fact that the proportion of amorphous polymer in these films is found to be maximum when the degree of formalization is between 10 and 20%.