Ethylbenzene solubility,diffusivity, and permeability in poly(dimethylsiloxane)

The pure‐gas sorption, diffusion, and permeation properties of ethylbenzene in poly(dimethylsiloxane) (PDMS) are reported at 35, 45, and 55 °C and at pressures ranging from 0 to 4.4 cmHg. Additionally, mixed‐gas ethylbenzene/N₂ permeability properties at 35 °C, a total feed pressure of 10 atm, and a permeate pressure of 1 atm are reported. Ethylbenzene solubility increases with increasing penetrant relative pressure and can be described by the Flory–Rehner model with an interaction parameter of 0.24 ± 0.02. At a fixed relative pressure, ethylbenzene solubility decreases with increasing temperature, and the enthalpy of sorption is −41.4 ± 0.3 kJ/mol, which is independent of ethylbenzene concentration and essentially equal to the enthalpy of condensation of pure ethylbenzene. Ethylbenzene diffusion coefficients decrease with increasing concentration at 35 °C. The activation energy of ethylbenzene diffusion in PDMS at infinite dilution is 49 ± 6 kJ/mol. The ethylbenzene activation energies of permeation decrease from near 0 to −34 ± 7 kJ/mol as concentration increases, whereas the activation energy of permeation for pure N₂ is 8 ± 2 kJ/mol. At 35 °C, ethylbenzene and N₂ permeability coefficients determined from pure‐gas permeation experiments are similar to those obtained from mixed‐gas permeation experiments, and ethylbenzene/N₂ selectivity values as high as 800 were observed. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1461–1473, 2000     

Sorption and dilation in poly(ethyl methacrylate)–carbon dioxide system

Sorption and dilation in the system poly(ethyl methacrylate) (PEMA) and carbon dioxide are reported for pressures up to 50 atm over the temperature range 15–85°C. The sorption isotherms were obtained gravimetrically. The dilation accompanying sorption was measured directly with a cathetometer. At low temperatures the sorption and dilation isotherms were concave toward the pressure axis in the low-pressure region and turned to convex with increasing pressure. As the experimental temperature approached and exceeded the glass transition temperature of 61°C, both isotherms became convex or linear over the whole range of pressure. Partial molar volumes of CO₂ in PEMA were obtained from sorption and dilation data, which were described well by the extended dual-mode sorption and dilation models developed recently. The temperature dependence of the dual-mode parameters and the isothermal glass transition are discussed.     

Thermally stable polyimide isomers for membrane-based gas separations at elevated temperatures

The temperature dependence of gas sorption and transport properties is examined for two polyimide isomers. The permeabilities and solubilities of five gases in these materials are reported over an extensive temperature range from 35 to 325°C. Also, the activation energies for permeation, the heats of sorption, and the activation energies for diffusion obtained for both polyimides are compared and correlated with physical properties of the polymers and penetrants. The influence of temperature on the selective properties of these membrane materials is discussed for three gas separations; He/N₂, CO₂/CH_4, and O₂/N_2. Thorough analysis of these data provides insight into the influence of the subtle difference in chain structure of the two isomers. The performance of the 6FDA-6F_p DA as a separation membrane at high temperatures suggests that it is an outstanding candidate for use in novel elevated temperature applications. ©1995 John Wiley & Sons, Inc.     

Sorption,diffusion, and permeation of ethylbenzene in poly(1‐trimethylsilyl‐1‐propyne)

The solubility, diffusivity, and permeability of ethylbenzene in poly(1‐trimethylsilyl‐1‐propyne) (PTMSP) at 35, 45 and 55 °C were determined using kinetic gravimetric sorption and pure gas permeation methods. Ethylbenzene solubility in PTMSP was well described by the generalized dual‐mode model with χ = 0.39 ± 0.02, b = 15 ± 1, and C^′_H = 45 ± 4 cm³ (STP)/cm³ PTMSP at 35 °C. Ethylbenzene solubility increased with decreasing temperature; the enthalpy of sorption at infinite dilution was −40 ± 7 kJ/mol and was essentially equal to the enthalpy change upon condensation of pure ethylbenzene. The diffusion coefficient of ethylbenzene in PTMSP decreased with increasing concentration and decreasing temperature. Activation energies of diffusion were very low at infinite dilution and increased with increasing concentration to a maximum value of 50 ± 10 kJ/mol at the highest concentration explored. PTMSP permeability to ethylbenzene decreased with increasing concentration. The permeability estimated from solubility and diffusivity data obtained by kinetic gravimetric sorption was in good agreement with permeability determined from direct permeation experiments. Permeability after exposure to a high ethylbenzene partial pressure was significantly higher than that observed before the sample was exposed to a higher partial pressure of ethylbenzene. Nitrogen permeability coefficients were also determined from pure gas experiments. Nitrogen and ethylbenzene permeability coefficients increased with decreasing temperature, and infinite dilution activation energies of permeation for N₂ and ethylbenzene were −5.5 ± 0.5 kJ/mol and −74 ± 11 kJ/mol, respectively. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1078–1089, 2000     

Mechanism of diffusion and sorption of carbon dioxide in poly(vinyl acetate) above and below the glass transition temperature

The pressure dependence below 1 atm of the apparent diffusion and permeation coefficients were observed by using the permeation time lag method for carbon dioxide in poly(vinyl acetate), which has a glass transition near room temperature, at temperatures ranging from 8 to 50°C. Above the glass transition temperature, pressure dependence of the diffusion and permeation coefficient has not been observed; hence, Fick's law with a concentration independent diffusion coefficient applies. On the other hand, in the glassy state, the apparent diffusion coefficient shows pressure dependence. Moreover, the behavior of the pressure dependence does not show a clear curve in the ranges between 30°C to 17°C. Above 17°C, the apparent diffusion coefficients show discontinuities, but below 17°C increase with pressure is regular. Using the theoretical prediction of Paul, a computer was used in the numerical calculation to determine the true diffusion coefficient and other dual sorption parameters. p]The compensated diffusion coefficients controlled only by Henry's law dissolution was described by three straight lines with two intersection in the form of Arrhenius plots, which give good agreement with both our results for He and Ar and those of Meares. It is assumed that beside the dual sorption mechanism, another effect, for instance some relaxation effect may also contribute to the diffusion for carbon dioxide in poly(vinyl acetate) near the glass transition temperature region.     

Transient and steady-state water vapor permeation through polymer films

Water vapor transport properties for the polymers Kapton H

1 Reference to a company or product name does not imply approval or recommendation of the product by the University of California or the U.S. Atomic Energy Commission to the exclusion of others that may be suitable.

and Parylene C were determined over a temperature range of 20 to 55°C. Activation energies and entropies for permeation as well as partial molar free energies, heats, and entropies of dilution were calculated for water vapor concentrations ranging from 3 × 10^?6 to 1 × 10^?3 mole H₂O per cm³ of polymer. Mylar A was tested to extend the available data for partial molar heats and entropies of dilution and to compare permeation and diffusion results with the corresponding values in the literature. Diffusion coefficients were measured using the time-lag technique of Barrer but employing a modified test apparatus. Equilibrium sorption isotherms at 30°C were obtained for Mylar A and Kapton H with a Cahn microbalance. The ratios of the permeability to diffusion coefficients as measured from time-lag experiments agreed with solubility coefficients within 3% for Mylar A and within 12% for Kapton H. Both polymers obeyed Henry's law. The results were interpreted in light of polymer polarity and morphology.     

Fluorinated polyimide nanocomposites for CO2/CH4 separation

The purpose of this project was to synthesize fluorinated polyimide (PI) nanocomposite membranes in order to study the gas permeation rates and selectivity of carbon dioxide and methane. PIs were synthesized from 2,2‐bis(3,4‐anhydrodicarboxyphenyl)hexafluoropropane (6F dianhydride, 6FDA) and 4,4′‐diaminodiphenyl ether (oxydianiline, ODA) into which were incorporated nanoparticulate additives as follows: in situ TiO_2, both plain and treated with dodecyl sulfate surfactant, and organo‐clay (Cloisite®‐10 Å) at loads of 1, 3, and 5 wt% to the polyamic acid. Polyamic acid films were solvent cast, cured at 200°C then post‐cured at 300°C and measured for permeation data and for thermal properties. Glass transition temperatures ranged from 124 to 140°C for the cured PIs and from 142 to 147°C for the post‐cured materials, the nano‐inclusions having little discernable effect on this property. Thermogravimetric analysis (TGA) data show that the inclusion of Cloisite® or TiO₂ caused a small decrease of thermal stability from 555°C to about 532 to 541°C. The inclusion of clay causes a decreased permeation rate while the addition of TiO₂ improves the rate and selectivity. Treating the nanofillers with surfactant decreases selectivity and marginally increases rate of permeation of CO₂. Post‐curing caused a darkening of the composites, but not the neat PI. This heat treatment also resulted in a significantly decreased permeation rate, but a significantly increased selectivity. The resulting material shows superior gas separation properties to the commercially available PI, Matrimid® produced by Ciba‐Geigy. Copyright © 2008 John Wiley & Sons, Ltd.     

Removal of Arsenic (III) from natural contaminated water using magnetic nanocomposite: kinetics and isotherm studies

The application of newly synthesized Fe₃O₄/TiO₂–SiO₂ that is modified with zinc (FTSZ) as a sorbent, for the removal of arsenic from contaminated water has been investigated in the present study. SEM, FTIR, XRD, BET, Zeta potential sizer (ξ) analyses are used to determine the sorbent characterization. The effect of the operational parameters such as initial pH, initial concentration, and the contact time were studied. In addition, the equilibrium behavior of FTSZ in As(III) removal was investigated in the temperature range of 20–40 °C. The results showed that the equilibrium data were fitted well with Langmuir than Freundlich isotherm model. The maximum monolayer adsorption capacity estimated by Langmuir isotherm was 24.010 mg g^?1. Thermodynamic parameters, ?H°, ?S° and ?G° were also calculated from graphical interpretation of the experimental data. Standard heats of sorption (?H°) were found to be endothermic and ?S° values were calculated to be positive for the sorption of As(III) onto the adsorbent.     

Polymer-Bromine Interactions. I. Interactions with Polyacrylonitrile

The present paper deals with the interactions of bromine with poly-acrylonitrile (PAN). Kinetics and equilibria of the sorption of Br₂ on PAN were studied at a concentration range of 0.01–0.1 mol/L and a temperature range of 25–40°C. Two kinds of sorption were found: a “reversible” sorption removable by water and an “irreversible” sorption removable by aqueous ammonia solutions. The irreversibly sorbed bromine is presumably linked by charge transfer to the nitrile groups of the PAN, as evidenced by UV spectra. The irreversible sorption follows the reversible sorption and is slower. Partition coefficients obtained from the linear Freundlich isotherms increased with temperature and, at 40°C, the values obtained were 97, 65, and 32 L/kg for the total, irreversible, and reversible sorptions, respectively. At 25°C the chemical potential, enthalpy, and change in entropy for the irreversible sorption were ?2.0 kcal/mol, 9.4 kcal/mol, and 38 cal·mol^?1·K^?1. Effects of a 6-day Br₂ treatment and ammonia rinse were: decrease in dry T _g from 74.5 to 61°C and in water from 38 to 35°C; no significant decrease in M _W ; decrease in tensile strength measured after the bromine stage, and improvement after ammonia stage; increased swollen dimensions from 57% in water to 75%; and stabilization of swollen dimensions upon drying. The results support the existence of two phases in the less ordered regions of PAN.     

Thermal mass changes of portland cement and SLAG cements after water sorption

A simple water sorption/retention (WS/WR) test, followed by stepwise static heating, was applied to the study of cement quality and the reactivity of its grain surface. The physically bound water and hence the specific surface both in the unhydrated and in the hydrated state were estimated as a function of the hydration time. Rehydration after heating at 220°C and contact with air was different inWS from that inWR samples, which indicates a difference in microstructure. XRD proved the formation of portlandite during the sorption test and eventual heating at 200°C, and its transformation into carbonates on contact with air, especially on heating at 400°C. The contents of these compounds were estimated from the mass difference between 400 and 800°C, which was compatible with the mass change between 220 and 400°C and this indicates surface reactivity. The test may serve for the routine study of cement. Dedicated to Professor Lisa Heller-Kallai on the occasion of her 65^th birthday     

EPDM as a selective membrane material in pervaporation

Various types of ethylene–propylene-diene terpolymers (EPDM) and crosslinking procedures have been investigated with pervaporation, vapor sorption, liquid sorption and gas permeation experiments. The EPDM parameters that have been changed are ethylene content, molecular weight, choice of third monomer, type of branching and various crosslinking procedures.The permeability coefficients were determined from pervaporation experiments and were about 40,000 Barrer for toluene and 700 Barrer for water. However, from vapor sorption measurements, a value of 22,000 Barrer for toluene was obtained which is somewhat lower. It should be realized that these data can only be compared qualitatively; the permeabilities obtained from sorption isotherms are derived data while in case of the pervaporation experiments it is experimentally measured.There is an indication that toluene behaves independently from water but the presence of toluene does influence the water flux during pervaporation. Gas permeation experiments resulted in permeabilities for CO₂, O₂ and N₂ of 120, 24 and 11 Barrer, respectively. No clear differences were found for both EPDM-variation and different crosslinking procedures.     

Effect of molecular weight on the diffusion coefficient of carbon dioxide in polystyrene

The permeability and time lag at pressures below 1 atm were measured for carbon dioxide in five polystyrene samples with different molecular weights at 25 to 40°C. The apparent permeability coefficient decreases with increasing carbon dioxide pressure and also decreases with increasing molecular weight of polystyrene, whereas the apparent diffusion coefficient calculated from time lag increases with pressure and is independent of molecular weight. Parameters for the partial-immobilization model were determined from the apparent diffusion and permeation coefficients by using a nonlinear least-squares optimization program without using sorption data. The results suggest that the void-saturation constant C′_H decreases as the molecular weight of the polymer increases or as the chain-end free volume decreases. The significance of these observation and their interpretation is discussed in terms of free-volume theory for glassy polymers.     

Argon sorption and partial molar volume in poly(ethyl methacrylate) above and below the glass transition temperature

Sorption and dilation isotherms for argon in poly(ethyl methacrylate) (PEMA) are reported for pressures up to 50 atm over the temperature range 5–85°C. At temperatures below the glass transition (T_g=61°C), sorption isotherms are well described by the dual-mode sorption model; and isotherms above T_g follow Henry's law. However, isotherms for dilation due to sorption are linear in pressure at all temperatures over the range investigated. Partial molar volumes of Ar in PEMA are obtained from these isotherms. The volumes are approximately constant above T_g (about 40 cm³/mol), whereas the volumes below T_g are smaller and dependent on both temperature and concentration (19–26 cm³/mol). By analyzing the experimental data according to the dual-mode sorption and dilation model, the volume occupied by a dissolved Ar molecule and the mean size of microvoid in the glass are estimated to be 67 129 ų, respectively. The cohesive energy density of the polymer is also estimated as 61 cal/cm³ from the temperature dependence of the dual-mode parameters.     

Pervaporation separation of water–acetic acid mixtures through poly(vinyl alcohol)-silicone based hybrid membranes

Hybrid membranes were prepared using poly(vinyl alcohol) (PVA) and tetraethylorthosilicate (TEOS) via hydrolysis followed by condensation. The obtained membranes were characterized by Fourier transform infrared spectroscopy, wide-angle X-ray diffraction and differential scanning calorimetry. The remarkable decrease in degree of swelling was observed with increasing TEOS content in membranes and is attributed to the formation of hydrogen and covalent bonds in the membrane matrix. The pervaporation performance of these membranes for the separation of water–acetic acid mixtures was investigated in terms of feed concentration and the content of TEOS used as crosslinking agent. The membrane containing 1:2 mass ratio of PVA and TEOS gave the highest separation selectivity of 1116 with a flux of 3.33 × 10⁻² kg/m² h at 30 °C for 10 mass% of water in the feed. Except for membrane M-1, the observed values of water flux are close to the values of total flux in the investigated composition range, signifying that the developed membranes are highly water selective. From the temperature dependence of diffusion and permeation values, the Arrhenius apparent activation parameters have been estimated. The resulting activation energy values, obtained for water permeation being lower than those of acetic acid permeation values, suggest that the membranes have higher separation efficiency. The activation energy values calculated for total permeation and water permeation are close to each other for all the membranes except membrane M-1, signifying that coupled-transport is minimal as due to higher selective nature of membranes. Further, the activation energy values for permeation of water and diffusion of water are almost equivalent, suggesting that both diffusion and permeation contribute almost equally to the pervaporation process. The negative heat of sorption values (ΔH_s) for water in all the membranes suggests the Langmuir's mode of sorption.     

Effect of structure on the temperature dependence of gas transport and sorption in a series of polycarbonates

The permeabilities and solubilities of five gases are reported for bisphenol-A polycarbonate (PC), tetramethyl polycarbonate (TMPC), and tetramethyl hexafluoro polycarbonate (TMHFPC) at temperatures up to 200°C. The temperature dependence of permselectivity is discussed in terms of solubility and diffusivity selectivity changes with temperature for CO₂/CH₄ and He/N₂ gas separations. The activation energies for permeation and diffusion and the heats of sorption are also reported for each gas in the three polycarbonates. Analysis of these values provides a better fundamental understanding of the effect of polymer-penetrant interactions and polymer backbone structure on the temperature dependence of the transport and sorption properties of gases in membrane separation processes. Important factors affecting the solubility and diffusivity selectivity losses or gains with increased temperature are also identified through correlation of these data with physical properties of the gases and polymers. These conclusions provide a framework for choosing the most promising membrane materials for particular gas separations at elevated temperatures. © 1994 John Wiley & Sons, Inc.     

Poly(acrylamide-co-itaconic acid) as a Potential Ion-Exchange Sorbent for Effective Removal of Antibiotic Drug-Ciprofloxacin from Aqueous Solution

This study describes equilibrium and kinetic sorption studies to remove the antibiotic drug Ciprofloxacin (CF) from aqueous solutions using poly(acrylamide-co-itaconic acid) [poly(AAm-co-IA)] as polymeric cation exchanger sorbent material. The co-polymeric sorbent was prepared by free radical induced aqueous polymerization and was characterized by FTIR spectroscopy and TGA analysis. In addition, its physicochemical parameters were also determined. The various isotherm models, when applied to equilibrium sorption data at 28°C, followed the following order: Langmuir > Temkin > Freundlich, with the fair maximum sorption capacity (Q _o ) of 178.5 mg g^?1. The kinetic sorption data, obtained at 28°C, was applied to kinetic models such as pseudo first order equation, pseudo second order model and a simple Elovich model. Based on regression values, the order of fitness of these models was pseudo second order > pseudo first order > simple Elovich model. The second order adsorption coefficients k_2adswere found to be 58 × 10^?3, 52.7 × 10^?3, 34.01×10^?3 g/mg min for drug solutions with initial concentrations of 10, 20 and 30 mg L^?1 respectively The sorption mean free energy from the Dubinin–Raduschkevich (DR) isotherm was found to be nearly 8.839 kJ mol^?1 indicating an ion-exchange mechanism for drug uptake. The optimum pH value of sorbate solution for drug uptake was found to be around 6.0. Finally, the antibacterial action of drug was investigated and it was found that after adsorption there was a decrease in bacterial growth inhibition efficiency of drug solution.     

Water Sorption Properties and Antimicrobial Action of Zinc Oxide Nanoparticles-Loaded Cellulose Acetate Films

In this work, ZnO nanoparticles loaded cellulose acetate (ZOLCA) films have been prepared and characterized by XRD, SPR and SEM analysis. The moisture permeation properties of the films have been investigated. The GAB isotherm model has been found to fit well on the moisture uptake data obtained at different temperatures. The monolayer sorption capacity χ_m was found to decrease from 0.059 to 0.0079 g water/g dry film with increase in temperature from 20 to 37°C. The isosteric heat of sorption, when studied in the lower water activity range of 0.04 to 0.10, was evaluated to be 46.55 to 87.29 kJ/mol. The water vapor permeability across the ZOLCA films was found to increase with temperature and activation energy of moisture sorption process was found to be 48.57 kJ/mol. These films have shown excellent antibacterial action against model bacteria E-Coli when investigated by qualitative and quantitative methods. Films exhibit great potential to be used as edible films to protect food stuff against microbial infections.     

Silica-containing polyetherimide hybrid films based on methyltriethoxysilane as precursor of inorganic network

Polyetherimide hybrid films containing 5–40% silica were prepared through a sol-gel process and thermal imidization by using methyltriethoxysilane as precursor of the inorganic network and a poly(amic acid) resulting from polycondensation reaction of 2,2-bis[4-(4-aminophenoxy)phenyl]propane with 2,2-bis[(3,4-dicarboxyphenoxy)phenyl]propane dianhydride. The properties of these films, morphology, water vapor sorption capacity, free surface energy, mechanical, thermal and electrical characteristics, were studied. The films exhibited good thermal stability, having an initial decomposition temperature above 470 °C and glass transition temperature in the range of 187–200 °C. They showed low dielectric constant and low dielectric loss in a large frequency field. Gas permeation tests using small molecules (He, N₂, O₂ and CO₂) at 6 bar and 30 °C indicated that the hybrid films containing higher silica content showed higher permeability for all the tested gases.     

Vapor-liquid equilibrium for the systems ethyl formate-methyl ethyl ketone,ethyl formate-toluene and ethyl formate-methyl ethyl ketone-toluene: new unifac parameters for interactions between the groups ACH/HCOO,ACCH2/HCOO and CH2Co/HCOO

Vapor-liquid equilibrium data are presented for the binary systems ethyl formate-methyl ethyl ketone (MEK) at 40°C and 50 °C and ethyl formate-toluene at 48°Cand 51°C and for the ternary system ethyl formate-MEK-toluene at 50°C. The measurements were carried out in a recirculation still similar to that proposed by Röck and Sieg. Vapor pressures of the pure substances were measured and the data correlated using the Antoine equation. The binary data were reduced by means of a maximum-likelihood procedure providing the relevant Margules, NRTL and UNIQUAC parameters.New UNIFAC interaction parameters between the groups ACH/HCOO, ACCH₂/HCOO and CH₂CO/HCOO have been obtained. These parameters have been used to predict the ternary data, and a comparison between the experimental and predicted values is presented.