The measurement of the diffusion coefficient and the sorption isotherm of water in paint films

An experimental technique together with a numerical model is proposed with which the diffusion coefficient and the sorption isotherm of water in paint can be measured. Inside a closed vessel, paint films are on stainless-steel plates. Water is present as water vapour in the air and in the paint. After blowing dry or wet air through the vessel for some time, the situation moves to a new equilibrium. The relative humidity of the air inside the vessel is measured as a function of time. From fitting the theoretical/numerical model against the experimental values, follow the diffusion coefficient and the sorption isotherm of water in the paint. The results show large scattering. When the independently measured sorption isotherm is used as an input parameter in the model, the fitting procedure gives much smaller scattering for the diffusion coefficient.     

Experimental Studies and Modelling of Sorption and Diffusion of Water and Alcohols in Cellulose Acetate

The sorption characteristics of water, methanol and ethanol vapours in cellulose acetate (CA) films were measured by microgravimetry. The sorption isotherms for water vapours in the CA film at different temperatures in the range 20–40°C do not obey the Flory equation over the whole water activity range. At high water activities, the sorption extent increases much faster with the water activity than it should according to the Flory approach. The isotherms over the whole water activity range can be fitted well by the ENSIC model, a new mechanistic model developed to account for the possibility of solvent cluster formation in the polymer material. Similar behaviour was observed for ethanol, which shows a lower tendency to form clusters, but higher affinity to CA. The sigmoidal shape found for the methanol sorption isotherm suggests a strong sorption on CA sites at low methanol activities. The Guggenheim–Anderson–De Boer equa-tion fitted well this isotherm. The diffusion coefficient, which was calculated from Fickian sorption kinetics at different solvent activities by curve fitting, was constant for water but increased with ethanol content in the membrane according to an exponential relationship characterized by a limit diffusion coefficient and a plasticization coefficient. The limit diffusion coefficient for water was two orders of magnitude larger than that for ethanol, but the activation energy for ethanol was twice as large. Methanol diffusion was only Fickian at a low solvent activity; the diffusion coefficient was one order of magnitude lower than that for water. © of SCI.     

Water‐transport properties in polyetherimide blends with a liquid crystal polymer

The effect of the addition of a liquid crystal polymer (Rodrun^®) on the sorption and transport properties of water through films of a polyetherimide (PEI, Ultem 1000) was investigated. A Cahn electrobalance was employed for measuring the water uptake by the polymer samples. Sorption measurements were made with films of PEI, Rodrun, and heterogeneous PEI/Rodrun blends at different water activities at 30°C. In all cases, diffusion and sorption coefficients decreased when the amount of Rodrun increased. Values of the water‐sorption isotherms were adjusted to different models. Permeabilities for the different samples were indirectly obtained using experimental values of the solubility and diffusion coefficients described above. Furthermore, permeabilities of the binary composite material were calculated on the basis of those of the pure components and some theoretical assumptions concerning blend morphology. Results were consistent with a Rodrun structure in the composite intermediate between a fibrillar and a laminar morphology. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 323–332, 1999     

In situ characterization of moisture sorption/desorption in thin polymer films using optical waveguide spectroscopy

The kinetics of moisture sorption/desorption in poly(terephthalate-co-phosphate) thin films was investigated in situ at T = 25 °C using optical waveguide spectroscopy (OWS). At low water activities, Fickian diffusion was observed for the initial phase of the sorption process, while at high activities, due to the clustering of water, a complex sorption behavior was found. The moisture sorption isotherms were analyzed according to both the Zimm and Lundberg model as well as the Brown model, which suggests the formation of clusters of water molecules in poly(terephthalate-co-phosphate) at water activities of α₁ = 0.58 or higher. The water diffusion coefficient decreases with increasing water activity, which also suggests water cluster formation. A biphasic desorption behavior was also observed upon decreasing the water activity from α₁ = 1 to 0. This study demonstrated the unique advantages of OWS in characterizing in situ the sorption/desorption behavior of penetrants in polymer thin films.     

Nonlinear kinetics of oxygen and nitrogen sorption on carbon molecular sieves

Equilibrium and kinetics of oxygen and nitrogen sorption in two different carbon molecular sieves (CMS) have been modeled. In both CMS materials, equilibrium characteristics are adequately described by the Langmuir model. However, for kinetics of sorption, one CMS followed classic Fickian diffusion, while the other sample did not. A mathematical model was developed which accurately describes both pure component as well as binary uptakes in both materials. Simple manipulation of the boundary condition of the diffusion process allows the model to accurately predict both Fickian and surface barrier diffusion. All parameters needed to estimate binary uptake rates are obtained from pure component uptakes and isotherms. In addition, the model predicts both pure component and binary diffusion rates with diffusion coefficients which are not concentration dependent.     

Erosion of a model rosin-based marine antifouling paint binder as studied with quartz crystal microbalance with dissipation monitoring (QCM-D) and ellipsometry

In this study two surface sensitive methods, i.e. quartz crystal microbalance with dissipation monitoring (QCM-D) and ellipsometry, were used for erosion measurements of a rosin-based marine antifouling paint binder. Thin films of the binder were applied on sensor surfaces by the means of spin-coating and the effect of water velocity over the paint film, water temperature or ionic strength on erosion was investigated. Both the acoustic QCM-D model and the optical ellipsometry model gave comparable erosion results. The initial 2–50 nm rapid erosion of the top layer was followed by steady-state erosion rate until end of experiment. For example, the steady-state erosion rate was 12 nm/24 h in artificial seawater at 23 °C and with a flow of 200 μl/min over the paint surface as measured with QCM-D. The erosion rate increased with increased velocity and increased temperature. Ionic strength had no effect on the erosion rate of this model binder. At low water velocities the surface layer was highly dissipative indicating a water filled surface top layer or the formation of deposits on the surface. New characterization techniques that are able to study the erosion mechanisms on the nanometre scale are sought for as the binders get more technically complex containing, for example, nanoparticles or enzymes. Surface sensitive methods could be used to rapidly screen the effect of different binder chemistries or paint additives on the erosion during the paint development process.     

Water sorption and water‐resistance properties of poly(vinyl alcohol)/clay nanocomposite films: Effects of chemical structure and morphology

A series of poly(vinyl alcohol)/sodium montmorillonite (PVA/NaMMT) nanocomposite films were prepared via a solution method, and their water sorption and water‐resistant properties were investigated as a function of clay content. The water sorption and water resistance properties were strongly dependent on the chemical structure and film morphology originating from the NaMMT content. The water diffusion coefficient and water uptake of the PVA/NaMMT nanocomposite films were obtained by best fits to a Fickian diffusion model. The diffusion coefficient and water uptake in the PVA/NaMMT nanocomposite films varied between 8.16 × 10⁻¹⁰ and 3.60 × 10⁻¹⁰ cm² s⁻¹ and 35.6 and 29.9 wt%, respectively. Both the diffusion coefficient and water uptake decreased as the content of NaMMT in pure PVA was increased. Additionally, the water resistance pressure (mm) of the PVA/NaMMT nanocomposite films increased with increasing NaMMT content. Contact angle analyses showed that the chemical affinity to water and the surface energy of the nanocomposite films decreased with increasing NaMMT content. Furthermore, the well‐dispersed and exfoliated structure in the nanocomposite films not only induced an increased tortuous path for water molecules to pass through, but also increased the molecular order. However, to enhance the water sorption properties and water resistance of hydrophilic PVA, further studies to increase the dispersion of clay particles and ensure desired morphological qualities such as crystallinity and molecular packing order in the PVA/clay nanocomposite films are required. POLYM. COMPOS., 36:660–667, 2015. © 2014 Society of Plastics Engineers     

Characterization of waterborne acrylic based paint films and measurement of their water vapor permeabilities

Recently, production of waterborne coatings has increased significantly as a consequence of strict pollution regulations. Waterborne coatings are sensitive to humidity, thus, their barrier properties with respect to permeation of moisture needs to be determined. Among various coating constituents, binder represents the matrix structure and its amount relative to the amounts of pigments and fillers can significantly affect the structure, hence the barrier property of the coating. In this study, waterborne acrylic based paints applied as protective coating on interior and exterior wall of the buildings are studied. The paint samples formulated with four different binder contents by a commercial paint company are used in the experiments. We first determine unknown ingredients of the paint samples using different characterization tools and then investigate the effect of the binder content on the structure of the paint films. In addition, water vapor permeability of the paint films is measured using a permeation cell. Results show that the barrier property of the waterborne acrylic based paint films against humidity decreases with decreased binder content due to uneven distribution of the pigments, consequently, porous structure formation in the films.     

Sorption isotherms of mixtures of polymers,proteins and electrolytes—Measurement data and model predictions

Blends of water-soluble polymers and proteins serve as a matrix for the immobilization of active components in coatings. Water absorption of these blends is important for the properties and the performance of the films. We propose an additive model for the calculation of water absorption into polymer blends that is able to describe the measured values for different concentrations and for different classes of additives. Sorption isotherms of the polymers polyvinylalcohol (PVA) and polyvinylpyrrolidone (PVP), the protein bovine serum albumin (BSA) and the salt sodium chloride (NaCl) were gathered using an automated gravimetric sample exchanger. The resulting sorption isotherms were modeled using the Flory–Huggins model for polymers and protein and an activity coefficient model for the salt. Sorption isotherms of mixtures were calculated using a model of weighted sums for the absorbed water. The prediction was able to describe the measured values with a deviation factor close to 1 above a water mass fraction of 0.1 in the film. For lower water mass fractions the relative deviations were larger due to the small values for the water absorption. This predictive model reduces the number of experiments necessary for the determination of sorption isotherms of mixtures.     

Immobilization influence on the water sorption and diffusion in poly(3-hydroxybutyrate)

The temperature dependency of water vapor sorption and diffusion in poly(3-hydroxybutyrate) (PHB) was studied for the first time. Equilibrium sorption and diffusion kinetics were determined by a quartz McBain's vacuum microbalance technique in the temperature range of 303–333 K. A probability of water molecule interaction with the polymer matrix was analyzed for wet PHB films by FTIR spectroscopy technique. Sorption isotherms are interpreted as the solution of free water molecules estimated by the Flory–Huggins equation and the sorption of water molecules immobilized on the carbonyl groups of PHB. The immobilization effect was described by a Langmuir-type equation. The dependency of diffusivity on water concentration was described in the frames of Fujita's immobilization model in which the growing function D_w versus C_w characterized the filling degree of carbonyl groups as sites of immobilization in the polymer. Enthalpy of free water sorption (12 kJ/mol) and water immobilization (42 kJ/mol), as well as the activation energy of water diffusion coefficients (71 kJ/mol), in noncrystalline areas of PHB were determined. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 981–985, 1999     

Interaction of CO2 with a series of detached organic films

Data obtained from gaseous sorption isotherms of CO₂ on eight organic films at three temperatures and three pressures were evaluated for evidences of chemisorption and physical adsorption. The rates of sorption, affected by both temperature and pressure, were analyzed by calculating the perameters of the Elovich equation and those of Barrer's solution of Fick's law for diffusion. Through a consideration of the Elovich parameters, the sorption coefficients, the limiting diffusion coefficients, and the activation energies for diffusion it appears that the rate of interaction of CO₂ with these organic films is primarily a diffusion-controlled process.     

Effect of different polymers on the efficiency of water‐borne methyl amine adduct as corrosion inhibitor for surface coatings

Styrene/acrylic emulsion copolymer and water‐based short oil urethane alkyd resin were used as binders to prepare water‐based, environmentally friendly paints by using 0.5% emulsified methylamine adduct as corrosion inhibitor. The choice of the two above‐mentioned binders was based on the fact that styrene/acrylic emulsion copolymer is a nonconvertible binder, whereas short oil urethane alkyd resin is a convertible binder. The physical, chemical, mechanical, and corrosion properties of the paint films were evaluated and compared with a commercially known anticorrosive water‐based paint. It was found that the prepared paints have unique desirable properties such as the following: they do not contain anticorrosive pigments (which contain heavy metals in their main chemical structure); they are solvent‐free; and they can be produced to match any color. Corrosion tests on the films of the formulated paints revealed that the short oil urethane alkyd resin is superior to the styrene/acrylic copolymer. Moreover, the corrosion inhibition properties of the paint films prepared from both binders are comparable with the commercially available paints containing anticorrosive pigments. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 879–885, 2002     

Water sorption and diffusion in starch/polyolefin blends

The kinetics of water sorption by starch filled polyolefins has been investigated using blends of commercial starch masterbatch with low density polyethylene (LDPE), high density PE (HDPE), and copolymers of ethylene with methyl acrylate (EMA), ethyl (EEA), AND n-butyl acrylate (EBA). Transient state diffusion coefficients (D) of water in the blends were determined using Fickian analysis of the initial stages of the sorption isotherms. Measured D values were several orders of magnitude lower than values reported for either pure starch of LIDPE by various investigators. Resin effects on D were on the order D_HDPE < D_LDPE ? D_EBA < D_EEA < D_EMA. The resin effects diminished as the starch content increased. The lower magnitude of D in the blends relative to pure LDPE was attributed to the sorption of water by the dry starch particles, in a manner similar to dual-mode sorption in glassy polymers. Copolymer effects were consistent with reduction in crystallinity caused by the comonomers. The dependence of the diffusion coefficient on starch content was not described by mixing models of heterogeneous systems of percolation theory.     

Effect of moisture‐ingress on adhesion energy in a metal oxide‐polymer system

This work quantifies the damage caused by moisture in a metal coating system under extreme weathering conditions, using Variable Radius Roll Adhesion Test (VaRRAT). Interfacial toughness (adhesion energy) between the metal oxide and the polymer in painted steel panels, studied by using VaRRAT, is observed to fall with increasing temperature and time of exposure to moisture. Possible cause for irreversible loss in adhesion energy in the paint system is attributed to the sorption of free water at the metal oxide–polymer interface. Different failure responses were observed in two different paint–metal systems. Adsorption or diffusion in the Henry's mode is rate controlling in green paints as indicated by the low activation energy of 12 kJ mol^?1. The white samples showed a high activation energy of 30 kJ mol^?1, indicating a mixed process of diffusion as well as chemical to be rate determining. Different paint/binder ratios are responsible for the different responses of these samples. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

Mathematical analysis of transport properties of polymer films for food packaging. II. Generalized water vapor models

Deterioration or spoilage of dehydrated food products stored in flexible packaging materials depends on the partial pressure of water vapor in the environment of the stored food. Mathematical analysis of the diffusion of water vapor through semipermeable polymer films using Nernst-Planck equations is combined with non-liner water sorption isotherms on food to establish criteria and optimum conditions for storage stability of dehydrated food. Langmuir, Brunauer-Emmet-Teller (BET), Halsey, Oswin and Freundlich isotherms are used for various ranges of water activity. It is shown that a single parameter, the permeability-sorption constant, based on the physical properties of the polymer and the sorptive properties of the food, accounts for both diffusion and adostption and can be used to accurately determine maximum storage times and can be used to accurately determine maximum storage times and to optimize the selection of packaging films. The theory is extended to thermodynamically compatible solute-polymer systems, where the polymer film is swollen appreciably by the diffusing species.     

Water sorption in poly(vinyl alcohol) membranes: An experimental and numerical study of solvent diffusion in a crosslinked polymer

The development of reliable mathematical models for mass transport in crosslinked polymers and their thorough experimental validation are of substantial interest in the design of technical membrane processes or the assessment of polymer performance when applications such as functional films and protective coatings are concerned.The present study aims at the joint experimental and numerical characterisation of mass transport during water vapour sorption into physically crosslinked poly(vinyl alcohol) membranes. A mathematical model comprising both phase equilibrium and the respective mass transport mechanisms is proposed and verified by means of in situ sorption kinetic measurements. Drawing on the independent determination of equilibrium solvent uptake, the comparison of model calculations and experimental sorption data demonstrates that water transport in the crosslinked polymer membrane is successfully described by pure Fickian diffusion with a simple exponential expression for the solvent diffusion coefficient to account for its pronounced concentration dependency, allowing the latter to be specified quantitatively.     

Studies of the chemical modifications of wool and their effects on the wool–water relationship. Part II. Wool-water relationships of modified and unmodified wool

The wool–water relationships of the modified wools prepared as described in Part I of this series have been studied. The drained water content of fabric and the solution isotherms and diffusion constants of water vapor into untreated and modified wools have been measured. Most of the treated wool fabrics showed considerable decreases in the drained water contents compared with the untreated wool. However, the degree of improvement depended markedly on the conditions of modification, particularly with the styrene grafted materials. In some cases values close to those of a comparable polypropylene fabric were found. The sorption isotherms also showed that the modifications reduced, substantially in some cases, the regains even when calculated on the wool content only. The diffusion constants were difficult to measure because of the heats of sorption causing temperature changes during the sorption; however, at lower regains this effect could be corrected. It was found that both the direct chemical modification and the grafted wools showed a diffusion behavior which was more characteristic of hydrophobic materials in that the diffusion constants tended to decrease with increasing concentration. At low humidities the diffusion constants were larger than in the untreated wool, but at higher humidities lower diffusivities were found with the modified wools.     

市政污泥吸附等温线模型和热力学性质

采用静态重量法测定了市政污泥在30℃、40℃、50℃下的吸附等温线,选用11个常见的数学模型对实验数据进行了拟合并对最佳模型进行了解析,通过净等量吸附热q_st、微分熵ΔS、扩散压力π、净积分焓q_in和净积分熵ΔS_in等指标评价污泥的热力学性质。试验结果表明,在温度恒定时,等温曲线属于Ⅱ型,GAB模型拟合效果最佳,能较好地反映平衡含水量随水分活度的变化。应用Clausius-Clapeyron方程,利用等温线模型计算净等量吸附热和微分熵,随着平衡含水率的增加,净等量吸附热和微分熵明显降低,调和平均温度T_hm与等速温度T_l不等,焓-熵补偿理论成立。在一定的水活度下,扩散压力随温度的升高而减小,在温度恒定的情况下,扩张压力随水分活度增大而升高。净积分焓随平衡含水率的增加而减小,而净积分熵在低平衡含水率时随平衡含水率的增加而减小,在30℃、40℃和50℃时分别达到最小值-75.698J/(K?mol)、-78.987J/(K?mol)和-82.687J/(K?mol),然后呈上升趋势。     

Evaluating barrier properties of organic coatings by water permeation and electrochemical methods

Water permeation, water absorption, d.c. resistance, and electrochemical impedance spectroscopy (EIS) measurements were performed on films of epoxy-polyamide used as binder in paint formulations. Barrier properties were found to be highly dependent upon the thickness of films. In thick films, water permeation measurements revealed the presence of pathways attributed to frozen holes, through which the flow is not governed by diffusion. In thin films, the presence of pinholes was detected by d.c. resistance and EIS measurements. LACTEC, área de Materiais — AMAT, Caxia Postal 19067, CEP 81531 - 990, Curitiba, Paraná, Brazil. Departamento de Química, Grupo de Processamento e Propriedades em Polímeros, Caixa Postal 675, CEP 13565-905, S?o Carlos, S?o Paulo, Brazil.     

Sorption behavior and preliminary pervaporation results of cross-linked polyvinylalcohol and polydimethylsiloxane membranes prepared for the separation of water-ethylacetate mixtures

Since pervaporation process is the coupling of solution and diffusion mechanisms, a sorption study was carried out with membranes prepared by cross-linking polyvinylalcohol (PVA) and polidimethylsiloxane (PDMS). Tartaric acid (Tac) was used as the cross-linking agent for PVA, and a commercial cross-linking agent was used for PDMS. Sorption experiments were carried out at 30-50°C temperature range in pure water and ethyl acetate using the films prepared. The PVA and PDMS films prepared preferentially sorb water and ethylacetate, respectively. A pervaporation study at 30°C was carried out for pure ethylacetate and pure water, and mixtures of ethylacetate containing 2 and 2.5 wt% water using 100 w m thick PVA membrane. The results indicate that the PVA membrane prepared is extremely selective for water.