Evidence for anomalous water vapor sorption kinetics in cement based materials

We used dynamic sorption balance measurements to evaluate the diffusivity for cement pastes with three different binders (OPC, OPC + 70% slag, OPC + 10% silica fume). The diffusion of water vapor in cement based materials is normally assumed to follow Fick's law of diffusion, but our results clearly show that Fick's law cannot completely describe the sorption process in our materials. In this paper we report the evidence for this anomalous sorption behavior and discuss a possible method to evaluate diffusivities from such measurements.     

Transport and sorption of water vapour in activated carbons

The adsorption of water vapour on microporous carbons derived from the carbonization of coconut shell has been studied. The adsorption and desorption characteristics of water vapour on the activated carbons were investigated over the pressure range p/p₀ 0–0.95 in a static water vapour system. In these experiments the process of water adsorption/desorption was investigated by both kinetic and equilibrium experimental data. Activated carbons differing by the degree of burn-off have shown the importance of the microstructure. A carbon enriched with nitrogen functions underlined the influence of the surface chemistry.     

Moisture sorption by modified-activated carbons

Modified activated carbons were prepared by the partial oxidation of activated maghara coal with concentrated nitric acid and potassium permanganate. This treatment fixes more oxygen on the carbon surface leading thus to the formation of carbon-oxygen complexes which act as primary centers for water adsorption. Not only the number of oxygen complexes that can determine the water adsorption properties but the pore size may be considered as another factor. The oxygen complexes outgassed as carbon dioxide can be qualitatively determined by neutralization with sodium hydroxide. These oxygen complexes are responsible for the irreversibly adsorbed water.     

Water vapor sorption kinetics of wood modified with glutaraldehyde

The modifying effects of Scots pine (Pinus sylvestris L.) wood with the crosslinking agent glutaraldehyde (GA) on the water vapor sorption kinetics were studied by curve fitting the experimental isotherm sorption data obtained using a Dynamic Vapor Sorption apparatus using the parallel exponential kinetics model (PEK model) and the Hailwood–Horrobin model (H–H model) for the isotherm. Both the H–H model and the PEK model provided good fits to the experimental data. Modification of wood with GA reduced both the time to equilibrium and the equilibrium moisture content (EMC). According to the PEK and H–H models, the reduction in EMC was mainly due to the decrease of moisture content (MC) associated with the slow sorption processes and polylayer water. The fast sorption processes and monolayer water were little affected by GA modification. Compared to the untreated control, the estimated total water absorbed by wood treated to a WPG of 20.9% at 100% RH decreased by 52.2%, by extrapolating the fitted curves derived from the H–H model. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

The water vapor sorption behavior of natural fibers

The water vapor sorption behavior of a range of natural fibers (jute, flax, coir, cotton, hemp, Sitka spruce) has been studied. The data were analyzed using the Hailwood Horrobin model for isotherm fitting and determination of monolayer moisture content. The Hailwood Horrobin model was found to provide good fits to the experimental data. The extent of hysteresis exhibited between the adsorption and desorption isotherms was dependent on fiber type studied and was larger with high lignin compared with low lignin content fibers. The area bounded by the hysteresis loop decreased as the isotherms were performed at progressively higher temperatures. This behavior is consistent with sorption interactions occurring with a glassy solid below the glass transition temperature. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Factors influencing contact angle measurements on wood particles by column wicking

The present work focuses on a capillary rise technique, referred to here as column wicking, for determining contact angles on wood particles. The liquid front rise versus time for different probe liquids has been measured for extracted and non-extracted spruce wood particles packed into glass columns. Wood is a porous, heterogeneous, and hygroscopic material. The sorption process of certain polar liquids in the wood substance, i.e. bulk sorption, is exothermic and causes swelling. This bulk sorption process and the resulting release of heat are observed as a distinct temperature increase within the columns during the wicking of water, formamide, and methanol. No temperature increase is observed for ethylene glycol, diiodomethane, and hexane. In some cases, the increase in temperature is observed in advance of the moving visible liquid front line. This may indicate that vapor is moving in advance of the liquid front, resulting in bulk sorption and the corresponding release of heat. An apparent non-linearity is observed when the square of the capillary rise is plotted versus time, mainly for water, formamide, and methanol. This non-linearity is strongly dependent on the probe liquid used and the variation in wood particle size. For the wicking of water, the bulk sorption, and hence the swelling of the wood particles, seems to appear instantaneously at the wetting front line, but for formamide and methanol a time delay is observed. The bulk sorption and resulting swelling of the wood particles strongly influence the determination of the effective interstitial pore radius between the particles, and thus the determination of contact angles by use of the Washburn equation.     

Study of humic acid adsorption on nanofiltration membranes by contact angle measurements

Membrane fouling is a major problem, which extent depends on the respective natures of the solute and membrane material. Membrane surface characterization under different fouling conditions may help in understanding the fouling mechanism. Such characterization was performed for the case of humic substances filtered on two nanofiltration membranes, using special contact angles measurements. The measured contact angles allowed the calculation of polar and non-polar contributions to the surface energy of dry, hydrated and fouled membranes. The results reveal significant differences in the two membrane behaviours and information about the way that fouling material may be adsorbed on membrane surface.     

The water vapor sorption behavior of flax fibers—Analysis using the parallel exponential kinetics model and determination of the activation energies of sorption

Sorption kinetic data for the interaction of water vapor with flax (Linum usitatissimum L.) were analyzed used the parallel exponential kinetics (PEK) model, with excellent fits to the data being obtained. The PEK model is the sum of two exponential kinetics processes (fast and slow), which have characteristic times and moisture contents associated with them. The slow adsorption and desorption processes exhibited important differences in their characteristic times, although hysteresis in the moisture contents was found to be predominantly associated with the fast process. The kinetics was examined over a range of relative humidity (RH) values and at different temperatures, enabling the determination of activation energies for the adsorption and desorption kinetic processes throughout the hygroscopic range (from 5–95% RH). © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

A three-parameter equation for describing the sorption of water vapor by chemisorptive fibres

Conclusions 1. A three-parameter equation for adsorption has been proposed which is suitable for describing the process of water-vapor sorption by chemisorptive fibres in the regions of monomolecular and polymolecular adsorption and cluster formation.2. The applicability of the proposed equation has been shown for describing water-vapor adsorption isotherms by the chemisorptive fibres TsM-A2, vion AN-1, and vion KN-1 in various ionic forms.Scientific Research Institute of Physics, Odessa State University. Translated from Khimicheskie Volokna, No. 5, pp. 28–29, September–October, 1993.     

Preparation of a coal surface for contact angle measurements

Coal specimens of different ranks were polished using silicon carbide abrasive papers (with a grit from #60 to #1200) and alumina powder of varying size (from 5 to 0.05 μm). The coal surface roughness and contamination (by alumina powder) were examined with both scanning electron microscopy and atomic force microscopy. The water advancing and receding contact angles were measured on such surfaces by varying the bubble size, using the captive-bubble technique. It was found that silicon carbide paper abraded all components of the coal surface, i.e. both organic and inorganic matter, to a similar depth. The roughness of the coal surface due to polishing with silicon carbide abrasive papers affected the contact angle hysteresis and the contact angle vs. bubble size relationship. Polishing of coal specimens with alumina powder reduced the microroughness of the coal surface but produced rough features at the macro level and caused mineral inclusions rising above the smooth organic matter. This phenomenon results from the heterogeneity of coal specimens consisting of minerals and macerals with different hardness values. The roughness at the macro level was easily distinguishable and had a significant impact on the measured contact angles when the coal surface was polished with coarse alumina powders, 5 and 1 μm in diameter. The effect of surface roughness on the advancing and receding water contact angles was significantly reduced (if not completely eliminated) when the coal surface was polished with a fibrous cloth (CHEMOMET) in the final step, after having been polished with 0.05 (0.06) μm alumina powder. Microscopic observation of the coal surfaces revealed that an appropriate ultrasonic treatment (8-10 min in an ultrasonic bath filled with water) and mechanical cleaning (polishing with a CHEMOMET cloth) of coal samples were required to remove the alumina particles left on the surface due to the previous polishing procedure. An improved methodology for coal surface preparation, prior to contact angle measurements, as proposed in this paper, includes polishing with a series of abrasive papers and 0.05 (0.06) μm alumina powder, polishing and cleaning with a fibrous cloth (e.g. CHEMOMET), and, finally, an extended cleaning in an ultrasonic bath filled with water.     

Water vapor sorption by amylose and cellulose acetates

Experimental sorption isotherms for amylose acetate (ADA) and cellulose acetate (CDA) are discussed in terms of the B.E.T. theory and the Hailwood–Horrobin theory. The B.E.T. theory predicted a good fit to most of the experimental isotherms up to 0.8 relative vapor pressure. A somewhat better fit was found with the solution theory of Hailwood–Horrobin over the entire range of relative vapor pressures. Annealing had little effect on the sorption properties of CDA, but significantly reduced sorption in ADA. This was attributed to a higher degree of ordering in the amylose polymer.     

Surface characterization of a semiconductor SiGe/Si heterostructure by contact angle measurements

For the integration of strained Si_1-xGe_x epilayers in future silicon technologies it is necessary to obtain flat planar interfaces. Thus, a good understanding of the growth mechanism and a good knowledge of the properties of this strained material are required. Many articles have dealt with these problems in the literature. In a previous study, atomic force microscopy (AFM) was used to analyze the morphological modifications in SiGe epilayers grown on Si. The different stages of surface evolution have been determined, particularly the onset of undulations. In this study, we have investigated these surface modifications using the contact angle measurement technique. We observed a correlation between the root mean square (RMS) values of the roughness obtained with AFM and the water contact angle values. We demonstrate that the contact angle measurement technique, taking certain precautions, allows the critical thickness, i.e. the thickness beyond which the undulation pseudo-period increases, to be determined accurately.     

Enhancement of polymer film adhesion using acid-base interactions determined by contact angle measurements

Quantitative correlations among surface chemical composition, acid-base thermodynamics, adhesion strength, and locus-of-failure are demonstrated. Four types of functional Teflon surfaces were prepared: two acidic (containing hydroxyl and carboxyl groups), and two basic (containing acetyl and dinitrobenzoate groups). X-Ray photoelectron spectroscopy (XPS) and attenuated total reflection infrared (ATR-IR) spectroscopy were used to characterize the molecular structure of the surface region. Contact angle adsorption isotherms were determined using phenol as an acidic probe and tetrahydrofuran (THF) as a basic probe. The carboxylated surface had a higher molar ?H^ab with basic THF than the hydroxylated surface, and neither surface had any interaction with the acidic phenol probe. The acetylated surface behaved as a base, interacting with phenol but not with THF, while the dinitrobenzoyl surface had both acidic and basic character. Adhesion tests were carried out in the 180° peel mode using post-chlorinated poly(vinyl chloride) as a model acidic adhesive between pairs of each type of film. The two surfaces with basic character had significant peel strengths, while the two acidic surfaces had very low peel strengths. Scanning electron microscopy (SEM) of the basic failure surfaces showed significant plastic deformation of the Teflon polymer, while the acidic failure surfaces showed no deformation. XPS analysis of the failure surfaces confirmed interfacial failure for the acid-acid pairs, and bulk FEP failure for the acid-base pairs. These results demonstrate directly and quantitatively the enhancement of adhesive bond strength through acid-base interactions.     

Uncertainty in contact angle measurements from the tangent method

The uncertainty in contact angles from sessile drops measured by the tangent method was estimated using a standard error propagation technique involving partial derivatives. If contact angles are <60°, then uncertainty of the tangent method appears to be quite small,≤ ± 2°. However, as θ values approach 90°, uncertainty increases asymptotically and can exceed ±5°.     

Techniques for measurement of water vapor sorption and permeation in polymer films

The accurate measurement of water vapor sorption and permeation in polymers is complicated because water has a tendency to adsorb on high energy surfaces, a relatively high heat of vaporization, and a high solubility in most polymers. These issues and the difficulties they cause in the design of sorption and permeation equipment are reviewed. Some new approaches to circumvent these problems are described. Data for bisphenol A polysulfone films are used to illustrate these approaches. © 1996 John Wiley & Sons, Inc.     

Effects of complexation on the water vapor sorption of polymer alloys

Water sorption measurements of the polyion complex between poly(p-styrenesulfonic acid) (PS_tS) and poly(4-vinylpyridine) (PVP) were carried out to study the effect of the Coulombic interactions between a polyanion and a polycation. The properties of the polyion complex were examined using infrared spectroscopy (IR), X-ray diffraction, X-ray photoelectron spectroscopy (XPS), and elemental analysis. It was found that the ionic bonds between and groups led to the formation of a 1:1 polyion complex between PS_tS and PVP. The nitrogen 1s level in the PS_tS/PVP polyion complex increased 2.1 eV above its level for PVP, indicating protonation of the pyridine group. In addition, at 293 K and 303 K the water sorption of the complex was larger than that of the sum of the component polymers. In the preceding paper, the water sorption properties of the polyion complex between poly(acrylic acid) (PAA) and PVP were studied. Compared to this complex, the PS_tS/PVP complex absorbed more water relative to its components. This may be due to the stronger acid strength of the over the ? COOH groups.     

Polymethyl methacrylate plus water: sorption kinetics and volumetric changes

Sheets of polymethyl methacrylate were weighed periodically in water and, after surface mopping, in air. A case was made for dual mode sorption kinetics with 40–60% of the water accommodated in microvoids and the remainder taken up by swelling. The kinetics of sorption departed from Fick's laws in ways which appeared to be mutually inconsistent. For example, the value of the diffusion coefficient appeared to increase not only in the course of sorption but also in desorption. This inconsistency was interpreted as an artifact due to a retarded swelling component of dual mode kinetics.