Entire Activity Range Research Articles

Sorption of vapours and liquids in PDMS: novel data and analysis with the GAB model of multilayer adsorption

Novel data on the sorption of vapours and liquids in cross-linked poly(dimethylsiloxane) (PDMS) elastomer at 25–40°C are reported together with the accurate and original way of parameterising the sorption isotherms by using the GAB (Guggenheim, Anderson and De Boer) model of multilayer adsorption. The GAB model has been found to provide acomparable or better representation of sorption isotherms than the Flory–Huggins model with a concentration-dependent interaction parameter and better than the ENSIC (Engaged Species Induced Clustering) model. This comparison holds true for poor solvents of PDMS (water, methanol), mild solvents (acetone, methyl acetate, dimethyl carbonate) and good solvents (tert-butyl methyl ether, tert-amyl methyl ether, cyclopentyl methyl ether). The GAB model provided anoticeably good assessment of the sorption of liquids and highly saturated vapours, which makes the model applicable within the entire activity range.

Vapor and Liquid Sorption in Matrimid Polyimide: Experimental Characterization and Modeling

The sorption of organic vapors of different chemical nature, molecular weight and polarity in glassy Matrimid 5218 polyimide films is measured and modeled in the entire activity range up to saturated vapor conditions. Experimental isotherms show several different peculiarities according to the nature of the solute component, consistent with the glassy character of the polymeric matrix. These features range from high vapor solubility coefficient at infinite dilution to swelling and plasticization of the polymer matrix depending on temperature and solute affinity. The various behaviors are then discussed by means of a thermodynamic model for properties of glassy polymeric phases. Indeed, the Non-Equilibrium Lattice Fluid (NELF) model is used to interpret the Vapor–Liquid-Equilibrium below Tg, while the corresponding equilibrium Lattice Fluid model was considered to the same purpose for the case of plasticization conditions in the system. This representation is able to describe consistently all different observed features and allows for a predictive procedure to reproduce solubility isotherms over a wide activity range.

Prediction of sorption in polymers using quantum chemical calculations: Application to polymer membranes

The knowledge of sorption of vapors and liquids in polymer membranes is important for the derivation of structure–property relationships between the polymer structure and membrane performance, which facilitates preparation of better membranes. Experimental methods for the determination of sorption are tedious and expensive. Conventional predictive methods are often inadequate. In this work, a combination of the Cosmo-SAC model based on quantum chemical calculations and the Flory–Rehner equation is used to predict the sorption in polymer membranes. A single adjustable parameter is used for each polymer. It is shown that the model can adequately predict sorption in several membrane polymers including block copolymers for both single component and two component sorption. In addition, two component sorption data can be predicted from single component sorption data. Further, the measurement of the sorption of a pure liquid in a polymer by simple swelling experiments is sufficient for obtaining initial estimates of single component sorption over the entire activity range as well as the two component sorption from liquid mixtures over the entire activity range. Hence, the use of complex equipment and tedious multicomponent sorption experiments can be minimized or avoided. This significantly simplifies the experiments required for measurement of sorption in polymer membranes.

Reformulating atmospheric aerosol thermodynamics and hygroscopic growth into fog, haze and clouds

Abstract. Modeling atmospheric aerosol and cloud microphysics is rather complex, even if chemical and thermodynamical equilibrium is assumed. We show, however, that the thermodynamics can be considerably simplified by reformulating equilibrium to consistently include water, and transform laboratory-based concepts to atmospheric conditions. We generalize the thermodynamic principles that explain hydration and osmosis – merely based on solute solubilities – to explicitly account for the water mass consumed by hydration. As a result, in chemical and thermodynamical equilibrium the relative humidity (RH) suffices to determine the saturation molality, including solute and solvent activities (and activity coefficients), since the water content is fixed by RH for a given aerosol concentration and type. As a consequence, gas/liquid/solid aerosol equilibrium partitioning can be solved analytically and non-iteratively. Our new concept enables an efficient and accurate calculation of the aerosol water mass and directly links the aerosol hygroscopic growth to fog, haze and cloud formation. We apply our new concept in the 3rd Equilibrium Simplified Aerosol Model (EQSAM3) for use in regional and global chemistry-transport and climate models. Its input is limited to the species' solubilities from which a newly introduced stoichiometric coefficient for water is derived. Analogously, we introduce effective stoichiometric coefficients for the solutes to account for complete or incomplete dissociation. We show that these coefficients can be assumed constant over the entire activity range and calculated for various inorganic, organic and non-electrolyte compounds, including alcohols, sugars and dissolved gases. EQSAM3 calculates the aerosol composition and gas/liquid/solid partitioning of mixed inorganic/organic multicomponent solutions and the associated water uptake for almost 100 major compounds. It explicitly accounts for particle hygroscopic growth by computing aerosol properties such as single solute molalities, molal based activities, including activity coefficients for volatile compounds, efflorescence and deliquescence relative humidities of single solute and mixed solutions. Various applications and a model inter-comparison indicate that a) the application is not limited to dilute binary solutions, b) sensitive aerosol properties such as hygroscopic growth and the pH of binary and mixed inorganic/organic salt solutions up to saturation can be computed accurately, and c) aerosol water is central in modeling atmospheric chemistry, visibility, weather and climate.

Physical properties of poly(ε‐caprolactone) layered silicate nanocomposites prepared by controlled grafting polymerization

AbstractPoly(ε‐caprolactone) (PCL) chains grafted onto montmorillonite modified by a mixture of nonfunctional ammonium salts and ammonium‐bearing hydroxyl groups were prepared. The clay content was fixed to 3 wt %, whereas the hydroxyl functionality was 25, 50, 75, and 100%, obtaining an intercalated or exfoliated system. The transport properties of water and dichloromethane vapors and the mechanical properties were investigated. The mechanical and dynamic mechanical analyses showed improvement of the nanocomposite elastic modulus in a wide temperature range. Interestingly, for the higher hydroxyl contents (50, 75, and 100%), the decrease of modulus at higher temperature, due to the PCL crystalline melting, did not lead to the loss of mechanical consistence of the samples. Consequently, they revealed a measurable modulus up to 120 °C, a much higher temperature with respect to pure PCL. Water sorption was investigated in the entire activity range, and a lower sorption was observed on increasing the hydroxyl content, up to the sample with 100% hydroxyl content, which turned to be completely impermeable, even in liquid water. The sample with 75% hydroxyl content showed a threshold activity (a = 0.4) below which it was impermeable to water vapor. Also, the diffusion parameters decreased when the hydroxyl content increased, up to the 100% sample, which showed zero diffusion. The diffusion parameters of an organic vapor, dichloromethane, also exhibited a decreasing value on increasing the hydroxyl content in the nanocomposites. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1466–1475, 2004

Improved amperometric method for the rapid and quantitative measurement of lipoxygenase activity in vegetable tissue crude homogenates.

An improved amperometric method for rapid (2 min) quantitative determination of lipoxygenase (LOX) activity in vegetable tissue crude homogenates is presented. Measured LOX activity was linear (R(2) > 0.99) throughout the entire activity range for green bean and for corn below 70% activity. The resolution was 0.4% or 1.11 micromol L(-1) s(-1) of oxygen. The limit of detection was 3.43 micromol L(-1) s(-1) of oxygen. The amperometric method was improved by encapsulating linoleic acid (LA) in beta-cyclodextrin (CD) resulting in a stable substrate-buffer solution at a pH below 8.0. Ethanol and Tween 20 were not effective in solubilizing high LA concentrations required by the assay. A prototype benchtop instrument with the potential for use in an industrial environment is also presented.

From binary to ternary systems: general behaviour and modelling of membrane sorption in purely organic systems strongly deviating from ideality by UNIQUAC and related models

This work reports the results of a study of the thermodynamic swelling behaviour of polar polymeric membranes in contact with purely organic liquid mixtures of strong polarity. The sorption of two aprotic/protic liquid mixtures ETBE/EtOH and AcOEt/EtOH in polyurethaneimide block copolymers was investigated over the entire activity range at 30°C. The polymers used were built from the same pyromellitimide hard blocks and oligomeric segments of different chemical natures (polyether: PTMG, PPG; polyester: PCL) and led to strongly non-ideal ternary systems. The sorption behaviour in these systems revealed particular features that cannot be easily anticipated from the vapour sorption isotherms obtained for the related binary systems. The occurring of strong sorption synergy effects, characterised by sorption coupling factors, led to very significant modifications of the polymer swelling to the detriment of the sorption selectivity. The strongest synergy effects were observed for the swelling of the PUI membranes in ETBE/EtOH mixtures. A comparative study of the semi-predictive modelling of the ternary system behaviours was described on the basis of the properties of the related binary systems and UNIQUAC or derived models. Accurate descriptions of the partial isotherms were obtained for most of the ternary systems investigated but the only system where sorption synergy effects were of particularly great importance.

Modelling of vapour sorption in polar materials: Comparison of Flory–Huggins and related models with the ENSIC mechanistic approach

This work focuses on the analysis of organic vapour sorption in polymer systems strongly deviating from ideality. The sorption of three different types of organics (i.e. alcohol, ether, ester) in polyurethaneimide block copolymers has been investigated using a microgravimetric technique over the entire activity range. For all the polyurethaneimides, sorption increases in the following order: ETBE<EtOH<AcOEt. A further analysis in terms of the Flory–Huggins (FH) theory generally shows a great discrepancy between experimental and calculated sorption values. This quasi-systematic failure could be ascribed to a fairly strong dependence of FH interaction parameter χ towards penetrant concentration, which cannot be accounted for by the FH theory. A theoretical modification of the FH theory, previously reported by Koningsveld and Kleintjens to account for the variation by a three-parameter law, was shown to be really efficient for sorption modeling over the entire activity range. Despite a systematic divergence for the very low sorption levels, an empirical modification of the FH theory using a power law χ= aφ b could also be an interesting alternative which requires only two parameters for a fairly good modeling for activities higher than 0.1–0.2. Considering the sorption phenomenon as a mechanical anisotropic process, the recent ENSIC approach, reported by Favre et al., proved its striking efficiency allowing the sorption modelling of all the sorption isotherms with a mean correlation coefficient R=0.9983.