Evidence of anomalous thermal expansion of water in cement paste

A comparative study of permeability measurement by thermopermeametry (TPA) and beam bending was performed on cement paste. To bring the two measurements into agreement, it is necessary to recognize that the pore solution has a thermal expansion coefficient about one and a half times that of bulk liquid and to account for viscoelastic stress relaxation during TPA experiments. The anomalous thermal expansion is not accounted for by the presence of ions in the cement paste pore solution.     

Dynamic determination of sorption isotherm of cement based materials

A dynamic method of determining sorption isotherm is proposed. Changes in humidity boundary conditions were applied to specimens of hardened cement paste having various water–cement ratios, as well as to autoclaved aerated concrete, and water adsorption rates were continuously recorded in a sufficiently short period. The diffusion equation was analytically solved and was fitted to the adsorption rates resulting in the rapid estimation of equilibrium moisture content. Results of equilibrium moisture content, the primary data of moisture capacity, showed good agreement with literature values. The adsorption rate measurement took 8 h for autoclaved aerated concrete and 12 h for hardened cement paste with a measurement interval of 60 s to predict an equilibrium moisture content at an ambient relative humidity.     

Wettability of colloid-imprinted carbons by contact angle kinetics and water vapor sorption measurements

As an example of nanoporous carbon materials, colloid-imprinted carbons (CICs) have been reported to have promising properties for use in a variety of applications. However, the wettability of these carbons has not been investigated as yet. In this work, CICs with different pore sizes (20–50 nm) were synthesized and heat treated at 1500 °C under a N₂ atmosphere. Heat treatment was found to not alter the nanoporous structure of these carbons, but did significantly decrease their oxygen content. Contact angle kinetics (CAK) and water vapor sorption (WVS) experiments were carried out to determine the wettability of the CICs, before and after heat treatment, showing that the as-synthesized CICs surfaces are much more hydrophilic when compared to commercial carbon black (Vulcan carbon, VC). The high hydrophilicity of the CICs is likely due to their high surface-specific oxygen atomic density (∼10 μmol m⁻²). Further heat treatment significantly decreases the hydrophilicity of CICs because of the removal of oxygen atoms from their surfaces, as also reflected by their cyclic voltammetric response in acidic solutions.     

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     

A sorption balance study of water vapour sorption on anhydrous cement minerals and cement constituents

The phenomenon of water vapour sorption by powdered cement constituents exposed to different relative humidities and temperatures was studied. The individual clinker phases C₃S, C₂S, C₃A, C₄AF, calcium sulfates and CaO were tested. Using a water sorption balance, the amount of chemically and physically sorbed water per unit of surface area of the powders and the relative humidity at which water sorption starts to occur on the phases were determined. Various cement clinker phases prehydrate very differently. CaO and C₃A were found to be most reactive towards water vapour whereas the silicates react less. CaO starts to sorb water at very low RHs and binds it chemically. Beginning at 55% RH, orthorhombic C₃A also sorbs significant amounts of water and binds it chemically and physically. Water sorption of C₃S and C₂S only begins at 74% RH, and the amount of water sorbed is minor. Calcium sulfates sorb water predominantly physically.     

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     

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.     

Bimodal behavior of C-S-H interpreted from short-term length change and water vapor sorption isotherms of hardened cement paste

Short-term length change isotherms (SLCIs) and water vapor sorption isotherms are useful to eliminate the effects of the colloidal features of C-S-H. SLCIs of hardened cement pastes initially conditioned by drying to equilibrium at different relative humidities (RHs) were measured over a complete RH loop between 5% and 98%. Based on the correlation between incremental thickness of adsorption and incremental strain from 40% to 98% RH, the basal spacing of C-S-H above 40% RH appears to increase further with increasing water vapor sorption. However, no correlation of these values was found from 5% to 40% RH and the basal spacing is considered stable in this domain. These properties of C-S-H are directly related to its isothermal volume change as a function of RH. It can be concluded that the dominant shrinkage driver above 40% RH is disjoining or hydration pressure and that below 40% RH is change in surface energy.     

The use of volume-averaging techniques to predict temperature transients due to water vapor sorption in hygroscopic porous polymer materials

Volume-averaging techniques developed for modeling drying processes in porous materials offer a convenient framework for analyzing vapor sorption in porous hygroscopic polymeric materials. Because of the large temperature changes associated with water vapor sorption in these materials (from 10° to 20°C), sorption/diffusion processes are best characterized through the coupled differential equations describing both the transport of energy and mass through the porous structure. Experimental and numerical results are compared for a variety of natural and man-made porous polymeric materials (textiles) using the volume-averaging technique. Boundary heat and mass transfer coefficients and assumptions about thermal radiative properties of the experimental apparatus are shown to influence results obtained with the numerical solution method. © 1997 John Wiley & Sons, Inc.

1 This article is a US Government work and, as such, is in the public domain in the United States of America.

J Appl Polym Sci 64: 493–505, 1997     

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.     

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     

Water and water vapor sorption studies in polypropylene–zeolite composites

Water and water vapor sorption to porous polypropylene–zeolite composites prepared by hot pressing have been studied as a function of zeolite loading. This work presents the first report on the effect of the zeolite as a filler on the water‐sorption properties of PP composites. Water swelling experiments were conducted at 25°C using pure PP and PP–zeolite films samples having different zeolite loadings (6–40 wt %). Because PP is a hydrophobic polymer, it does not sorp any water, but the composites having 10, 20, 30, and 40% zeolites have sorbed 0.63, 1.00, 1.72 and 3.74% water, respectively. The zeolite itself at the same conditions sorbed 24.5% water. As the filler loading in the composites increased, equilibrium uptake values increased also. On the other hand, water vapor sorption and kinetics has been studied using a Cahn 2000 gravimetric sorption system. Within in the range of 0.35–0.95% water vapor was adsorbed by the composites containing 10–40 wt % zeolites. Experimental effective water vapor diffusivities of the composite films was about one order of magnitude higher (10‐fold) than the experimental water diffusion coefficient in composites. The transport of water in composites was slower than that in the liquid water due to the longer diffusion pathway and adsorption on the surface of the composites. Although the liquid water may fill all the voids in the composite, water vapor is adsorbed on the surface of the zeolite only. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3069–3075, 2003     

Modeling of vapor sorption in glassy polymers using a new dual mode sorption model based on multilayer sorption theory

Conventional dual mode sorption (CDMS) model is one of the most effective models in describing vapor sorption isotherms with a concave towards the activity axis in glassy polymers, while engaged species induced clustering (ENSIC) model has been approved to be highly successful in modeling vapor sorption isotherms in polymers with a convex to the activity axis (BET type III) over a wide range. However, neither of them is effective to describe other types of vapor sorption isotherms, especially sigmoidal isotherms. The Guggenheim–Anderson–de Boer (GAB) model fits extremely well with sigmoidal isotherms such as some vapor especially water vapor sorption data in food and related natural materials. However, one assumption of the GAB model for vapor sorption in glassy polymers is inconsistent with the fact that there are two species of sorption sites as the CDMS model assumes. Based on multilayer sorption theory on which the Guggenheim–Anderson–de Boer (GAB) model is based, a new dual mode sorption (DMS) model for vapor sorption in the glassy polymers is deduced. The mathematical meanings and the physicochemical significances of the parameters in the new model are analyzed. The new model has been verified experimentally by some special cases. Comparisons of the new DMS model with the CDMS and the ENSIC models prove that only the new model fits extremely well with all types of vapor sorption isotherms in the glassy polymers.     

Capillary condensation-induced anomalous water sorption in urethane-based coatings exposed to high humidity conditions

In this work, the water uptake of crosslinked urethane-based coatings in high humidity conditions as a function of crosslinking temperature was investigated. The water uptake values were measured using an electrochemical impedance spectroscopy technique by applying the Brasher–Kingsbury procedure. Water uptake values as high as 200% were observed in the current research. These anomalous results were explained based on capillary condensation of diffused water molecules in the nano-metrically (or nano-scale) rough hydrophilic surfaces of the pores formed by thermal degradation of the polyurethane network. The water uptake value is at its minimum when an effectively pore-free tight network formed at moderate crosslinking conditions.     

Gel–water relationships in hydrophilic polymers: Thermodynamics of sorption of water vapor

A thermodynamic study was conducted of water vapor adsorption on four hydrophilic polymers (agar, carboxymethyl cellulose, gelatin, and maize starch) at 12 and 25°C. Monolayer coverage amounted, after correction for crystallinity, respectively, to 0.93, 1.46, 0.51, and 0.77 mol water/mol monomer. Evidence is adduced from the Bradley equation and thermodynamic data to indicate that at least during coverage with the second layer of water, the energy of adsorption is greater than that due to condensation alone. Differences in the amount of sorption and in the trend of values of ΔS?° and ΔH?° with the amount of sorbed water are related with differences in the strength of intermolecular association as affected by steric hindrances.     

Moisture equilibrium of cement based materials containing slag or silica fume and exposed to repeated sorption cycles

Water vapor sorption isotherms are essential data in models to predict the service life of cement based structures. This study investigates the influence of water to binder ratio (0.4, 0.5 and 0.6), and the presence of two SCMs (70% slag and 10% silica fume) on sorption isotherms, both in the hygroscopic and in the super-hygroscopic relative humidity (RH) ranges.In the present paper desorption isotherms are divided into different parts based on the Jennings CM-II model of the C–S–H structure. The samples with silica fume and slag have higher moisture content than OPC samples, but with a higher amount of gel pores and lower amount of capillary pores. At low RHs all samples have similar desorption curves and the introduction of SCMs induces only a slight increase in the BET surface area.     

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.     

Sorption of water vapor by various cellulosic materials

Conclusions The form of the dependence between the values of the water surface and the heat of wetting in processes of water vapor sorption by various cellulosic materials has been refined.The connection of water and thermal effects with the degree of crystallinity of cellulosic materials has been shown.Translated from Khimicheskie Volokna, No. 4, pp. 28–29, July–August, 1983.     

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.