Water Diffusion Process Research Articles

Water Absorption Behavior and Its Influence on Properties of GRP Pipe

With the rapid development of glass-fiber reinforced plastic (GRP) pipes in civil infrastructure under different environments, it is essential to understand the fundamental mechanisms responsible for the pipe failure. However, research reports on water absorption behavior and its influence on the performance of GRP pipe are few in the literatures. This study provides test results of water diffusion in a GRP pipe wall and its influence on the properties of the pipe. When the environment is water, it attacks each component of the GRP pipe. In this study, the water absorption behavior of three different types of GRP pipe is recorded. One of them (UP-A pipe) presents near-Fickian behavior, the other two types of pipe behave like a two-stage diffusion. A model developed from Fick's law is used to predict the water diffusion process for the three pipes. The prediction agrees well with the experimental data for the UP-A specimen, while the same cannot be transferred to EP-A and UP-B specimens because of the abnormal non-Fickian process. The influence of moisture on flexural properties, interlaminar shear strength, and viscoelastic properties of a GRP pipe is also discussed.

Highly oriented tunable wrinkling in polymer bilayer films confined with a soft mold induced by water vapor

The authors report the formation of highly oriented wrinkling on the surface of the bilayer [polystyrene (PS)/poly(vinyl pyrrolidone) (PVP)] confined by a polydimethylsiloxane (PDMS) mold in a water vapor environment. When PVP is subjected to water vapor, the polymer loses its mechanical rigidity and changes to a viscous state, which leads to a dramatic change in Young's modulus. This change generates the amount of strain in the bilayer to induce the wrinkling. With a shape-controlled mold, they can get the ordered wrinkles perfectly perpendicular or leaned 45 degrees to the channel orientation of the mold because the orientation of the resultant force changes with the process of water diffusion which drives the surface to form the wrinkling. Additionally, they can get much smaller wrinkles than the stripe spacing of PDMS mold about one order. The wrinkle period changes with the power index of about 0.5 for various values of the multiplication product of the film thicknesses of the two layers, namely, lambda approximately (h(PS)h(PVP))(1/2).

An Analytical Hydrological Model for the Study of Scaling Issues in Land Surface Modeling

Abstract Besides the atmospheric forcing such as solar radiation input and precipitation, the heterogeneity of the surface cover also plays an important role, especially in the distribution characteristics of the latent heat flux (LE). In this study, scaling issues are discussed based on an analytical hydrological model that describes the transpiration and diffusion processes of soil water. The solution of this analytical model is composed of a transient part that depends primarily on initial conditions and a steady part that depends on the boundary conditions. To know how sensitive the different averaging approaches are to the initial conditions, three initial profiles are chosen that cover the prevailing soil moisture regimes. After analyzing its solution, the study shows that 1) upon reaching the steady state, directly taking an average of soil properties will cause systematic overestimation in the calculation of area-averaged LE. For an initially very dry condition, averaging of a sandy soil and a clay soil can cause a percentage error as large as 40%. 2) For vegetation growing on sandy soils, a direct averaging of the transpiration rate results in persistent overestimation of LE. For vegetation growing on clay soil, however, even after reaching the steady state, averaging of two water extraction weights can be either an overestimation or an underestimation, depending on which two vegetation types are involved. 3) During the interim stage of drying down, averaging of the soil/vegetation properties can lead to either an overestimation or an underestimation, depending on the evolving stage of the soil moisture profile. 4) The initial soil moisture condition matters during the transient stage of drying down. Different initial soil moisture conditions yield different scenarios of underestimation and overestimation patterns and a differing severity of errors. The simplicity of the analytical model and the heuristic initial soil profiles make the generalization easier than using sophisticated numerical models and make the causality mechanism clearer for physical interpretations.

Slab dehydration in the Earth's mantle transition zone

Because of the high water solubility in wadsleyite and ringwoodite, the mantle transition zone is possibly a large water reservoir. The potentially high water content of the Earth's mantle transition zone is a key element of several global mantle dynamic models. Nevertheless, to keep the transition zone relatively wet, the tendency for convection to distribute water over the entire mantle has to be offset by other mechanisms. One such mechanism could be linked to the dehydration of the slab. Studies of slab dehydration mainly focus on hydrous minerals phase diagrams that provide the depth of water exsolution. In this study, we investigate the water diffusion process that occurs prior to such exsolution. The diffusion process is controlled by both chemical gradients and thermal gradients via the temperature dependence of water solubility. We have addressed how this diffusion phenomenon influences slab water transport into the transition zone by developing a theoretical model of coupled thermal and chemical diffusion in a flat lying slab stalled in the transition zone. Model solutions demonstrate that even if intrinsic water solubility is decreasing with increasing temperature (which normally would act to impede a chemical diffusion from the slab), the water concentration profile adjusts to reduce the adverse effects of temperature-dependent solubility. The self-adjustment entails the concentration of water reaching a local maximum below the top edge of the stagnant slab; under specific conditions, this concentration maximum can reach the solubility limit and thus exsolve fluid (i.e. create of hydrous melt or aqueous silicate fluid). Consequently, model water flux computations are relatively independent of solubility variation and indicate that much of the water flux introduced by relatively well hydrated slabs is taken up into the transition zone by diffusion.

Evaluation of the moisture content in phenolic resin via acoustic measurements

Moisture absorption is a water diffusion process known to alter many of the mechanical properties of polymers and polymer-based composites. Ultrasonic waves are sensitive to such changes of properties and allow in situ measurements to be performed. This paper presents linear and nonlinear ultrasonic measurements on 12 phenolic resin plates with water contents ranging from 0% to 5% of their dry mass. Linear parameters are evaluated by an insertion/substitution spectroscopy method yielding to a representation of the evolution, with frequency, of the attenuation and of the phase velocity of acoustic waves propagating in each sample. Nonlinear β coefficient of each sample is determined by a contact phase modulation method. The evolution, with moisture content, of acoustic parameters such as the attenuation and the phase velocity of acoustic waves propagating at a given frequency, the slope of their attenuation with frequency, and the β coefficient of each sample is then studied. Results are discussed in terms of sensitivity.

Water Diffusion Behavior in Epoxy Resins with Various Fluorine Contents

In this work, novolac resin with perfluorinated side chains was synthesized and cured with o-Cresol novolac epoxy resin to obtain epoxy resins with various fluorine contents. Attenuated total reflection Fourier transform infrared spectroscopy (ATR/FT-IR) was used to monitor the in situ water diffusion process in these systems. The diffusion coefficient of water first increased and then slightly decreased with increasing fluorine content, which could be attributed to two opposite effects induced by perfluorinated side chains: enhanced hydrophobicity and increased free volume. In addition, generalized two-dimensional (2D) correlation analysis was employed to investigate both the sorption and the desorption process of water diffusion, and two kinds of water molecules, named bound and free water, were found. It was interesting to find that in the sorption process, the change in the population of bound water molecules occurs earlier than the change in the population of free water molecules, while in the desorption process, the sequence was reversed.

Inverse Finite Element Analysis of Technological Processes of Heat and Mass Transport in Agricultural and Forest Products

Due to complexity of agricultural and forest products, the mathematical model coefficients are often dubious, as experimental determination of their values leads to erroneous results. To solve this problem an inverse finite element analysis software was developed to identify coefficient values of the heat and mass transport model and to predict and visualize the processes. The model reflected 3D structure of investigated systems comprising the heat conduction and moisture diffusion in heterogeneous, anisotropic, and irregularly shaped products represented by wood and cereal grain kernels. Test cases used to validate the software covered identification of the thermal conductivity, convective heat transfer coefficient, diffusion coefficient, equilibrium moisture content, and convective mass transfer coefficient in pine and beech wood, and also in corn. Implementation of the proposed optimization algorithm and improvement of the software functionality resulted in more effective and accurate identification of the coefficient values, demonstrated by increased accuracy and reliability of predicting the heat conduction and water diffusion processes.

OTIMIZAÇÃO DE EXTRAÇÃO DE INULINA DE RAÍZES DE CHICÓRIA

Chicory root is the most important tuberous root for industrial production of inulin, which has high fructose content. Inulin is a stored carbohydrate, which can be found in more than 30,000 vegetable products. It is a fructooligosaccharide that is not digestible but it is selectively utilized by bifid bacteria in the large intestine, making inulin-type fructans the prebiotic prototype. Recently, inulin was identified as an ingredient that substitutes fat or sugar. In this work, inulin samples were extracted from chicory roots by a hot water diffusion process. The methodology consisted of the election of two levels of bath temperature, to the water: root ratio (water mass/root dry mass) and their combinations in a experimental design to execute the experiment. The analysis of variance (ANOVA) was done through the statistical 5.0 software. A second order polynomial model, with the response surface and contour plot was generated and it allowed the choice of temperature and water: root ratio that gives the highest inulin concentration.

Heat conductivities of insulation mats based on water glass bonded non-textile hemp or flax fibres

Heat insulation mats based on water glass bonded non-textile flax and hemp fibres were fabricated via a pilot plant, and their heat conductivities investigated. Under the influence of various factors like moisture content, water sorption and diffusion processes, fibre characteristics and heat radiation as well as thickness and apparent density, heat conductivities in the range of 0.0392–0.0484 W/mK for flax fibre mats and 0.0441–0.0592 W/mK for hemp fibre mats were obtained. Strong interactions between the fibre characteristics on the one hand and the water sorption and diffusion processes, the heat radiation, the apparent density and the thickness on the other hand were found. Investigations of tensile strengths and dimension stabilities indicate that the isolation mats are easy to handle and a structural alteration of an overall construction will not occur.

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.

Electrochemical Impedance Spectroscopy Study on the Diffusion Behavior of Water through Epoxy Coatings

The diffusion behavior of water through epoxy coatings with micaceous iron oxide (MIO) at different pigment volume concentration (PVC) was studied by EIS techniques. Experimental results showed that, in the initial diffusion period, the diffusion processes of water through epoxy coatings immersed in 0.5 M sodium chloride (NaCl) solution followed Fick's second law. The diffusion coefficients of water through the coatings were also calculated. Within the PVC values that were studied, the diffusion coefficients of water through epoxy coatings decreased with increasing PVC, indicating that the barrier property of the pigment was the main factor affecting the water diffusion behavior.

Water diffusion into epoxy resin: a 2D correlation ATR-FTIR investigation

The water diffusion process in a novolac epoxy resin (EP) was studied by 2D ATR-FTIR spectroscopy, the originally broad water OH bands in 1D-IR spectra can be effectively differentiated into three bands, located at 3610, 3460 and 3240 cm −1, respectively. The bands at 3460 cm −1 (antisymmetric) and 3240 cm −1 (symmetric) are assigned to the OH stretching vibration of water fully hydrogen-bonded with other water molecules, while the 3610 cm −1 band could be attributed to the stretching vibration of water partially hydrogen-bonded with epoxy resin. The mechanism of the water diffusion process in EP is also discussed.

Two-Dimensional ATR−FTIR Spectroscopic Investigation on Water Diffusion in Polypropylene Film: Water Bending Vibration

Two-dimensional (2D) correlation ATR−FTIR spectroscopy was used to study the dynamic diffusion behavior and state of water in syndiotactic polypropylene (S-PP). The 2D asynchronous spectra of water bending band clearly reveal that there are three separate bands in the 1800−1500 cm-1 region. These three bands at 1676, 1645, and 1592 cm-1 are assigned, respectively, to the aggregated water with strong hydrogen bond, the aggregated water with moderate strong hydrogen bond, and the “free water”. On the basis of this approach, the following mechanism for the diffusion process of water in S-PP has been proposed: the aggregated water molecules first diffuse into the polymer during the diffusion process. The water molecules with strong hydrogen bond will diffuse slower than water with moderate strong hydrogen bond because of their large size. In the late stage of the diffusion process, some aggregated water molecules in the PP matrix are forced to dissolve into the “free water” form.

Modeling the water transport properties of casein-based edible coating

A mathematical model able to predict the water transport properties of casein-based edible coating is presented. The model consists of two parts. The first is aimed to describe the water solubilization process into the investigated film, and it was derived taking into account the presence of both “bound water” and “free water”. The second is intended to describe the water diffusion process, and it was derived considering both the dependence of water diffusion coefficient of local water concentration and the superposition of polymer relaxation to stochastic diffusion. To validate the model both water sorption isotherm and sorption kinetics of the investigated film were determined at 25 °C. The proposed model was successfully fitted to both sorption and diffusion data, corroborating the validity of the hypothesis used to derive it.

Fluorescence labels to monitor water absorption in epoxy resins

Water uptake phenomena was studied in a group of commercial epoxy based thermosets using gravimetric and fluorimetric analysis. The different epoxy formulations were labeled with two dansyl derivatives differing in the spacer length between the chain and the fluorophore moiety. The fluorimetric method consisted of monitoring the changes in the first moment of the dansyl emission band as a function of water immersion time. Using the fluorescence, it was possible to obtain the parameters that govern the water diffusion process and there was a good concordance with gravimetric results. Furthermore, the fluorescence response of the dansyl moieties was used to study the effect of the molecular structure of the polymers in the water absorption process.

Water absorption in epoxy resins by electronic energy transfer

AbstractWater absorption of an epoxy resin was studied by steady‐state fluorescence spectroscopy and gravimetry. It was found that the intrinsic emission of the epoxy resin could be modified selecting an adequate excitation wavelength. The epoxy component of the resin was labelled with a trans‐4‐nitro‐4′‐aminostilbene fluorescent probe. Using an excitation wavelength of 340 nm it was possible to induce energy transfer to the suitable acceptor trans‐4‐nitro‐4′‐dialkylaminostilbene (NDAS). The relative fluorescence intensity I433/I596 was used as a convenient means to follow the quenching effect of water on the emission of NDAS when excited via energy transfer. It was found that both the relative intensity and the water content increase linearly with the square root of diffusion time in the early stages of the process. The apparent Stern–Volmer constants for the quenching of the fluorophore, when excited directly in a fluid THF solution or in the polymer matrix, were very similar but lower than when the fluorophore was excited via energy transfer. It was concluded that, at least in the early stages of the water diffusion process, the interchromophoric distance should increase.© 2002 Society of Chemical Industry

Effect of PVC on the diffusion behaviour of water through alkyd coatings

The diffusion behaviour of water through alkyd coatings with micaceous iron oxide pigment at different pigment volume concentration (PVC) was studied by EIS and SEM techniques. The diffusion coefficients of water through the coatings were also calculated. The experimental results showed that, in the initial diffusion period, the diffusion processes of water through alkyd coatings immersed in 0.5 M NaCl followed the Fick's second law. Within the PVC values which have been studied, the diffusion coefficients of water diffusing through alkyd coatings initially decreased with increasing PVC, reaching a minimum value at 60%, and then increased with increasing PVC. When PVC was less than 60%, the barrier property of pigment was the main factor affecting the water diffusion behaviour. However, the coatings' microstructure played an important role when PVC was greater than 60%.

NMR imaging of high-amylose starch tablets. 1. Swelling and water uptake.

Pharmaceutical tablets made of modified high-amylose starch have a hydrophilic polymer matrix into which water can penetrate with time to form a hydrogel. Nuclear magnetic resonance imaging was used to study the water penetration and the swelling of the matrix of these tablets. The tablets immersed in water were imaged at different time intervals on a 300 MHz NMR spectrometer. Radial images show clearly the swelling of the tablets and the water concentration profile. The rate constants for water diffusion and the tablet swelling were extracted from the experimental data. The water diffusion process was found to follow case II kinetics at 25 degrees C. NMR imaging also provided spin density profiles of the water penetrating inside the tablets.

Effect of PVC on the Diffusing Behavior of Water through Alkyd Coatings

The diffusion behaviour of water through alkyd coatings with micaceous iron oxide pigment at different pigment volume concentration (PVC) was studied by EIS and SEM techniques. The diffusion coefficients of water through the coatings were also calculated. The experimental results showed that, in the initial diffusion period, the diffusion processes of water through alkyd coatings immersed in 0.5 M NaCl followed the Fick's second law. Within the PVC values which have been studied, the diffusion coefficients of water diffusing through alkyd coatings initially decreased with increasing PVC, reaching a minimum value at 60%, and then increased with increasing PVC. When PVC was less than 60%, the barrier property of pigment was the main factor affecting the water diffusion behaviour. However, the coatings' microstructure played an important role when PVC was greater than 60%. (C) 2002 Elsevier Science Ltd. All rights reserved.

D�termination indirecte des coefficients de diffusion de la vapeur d'eau dans les directions tangentielle et radiale du bois de h�tre

Indirect determination of tangential and radial steam diffusitivity of beech. In order to characterize the diffusion process of water in the hygroscopic range of wood, we propose to evaluate initially the diffusion coefficients of water vapour in the three orthotropic directions of wood. The diffusion coefficients of water vapour are deduced from the diffusion coefficients of an inert solute (helium) measured in a diffusion cell, type Wicke and Kallenbach, being in an unsteady state. The diffusion coeff icients in the radial and tangential directions measured at 30 °C are independent of absolute moisture content of wood. The values we f ind agree with ranges of variations given in the literature. The diffusion coefficient in the radial direction is roughly higher th an the diffu- sion coefficient in the tangential direction, probably due to the rays in the radial direction. diffusion coefficient / hygroscopic range / beech / steam diffusivity / Wicke and Kallenbach diffusion cell