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.     

The effect of humidity on water sorption in photoresist polymer thin films

A quartz crystal microbalance technique has been utilized to measure water sorption and desorption in three photoresist polymers: poly(p-hydroxystyrene), novolac, and bis-triflouromethyl carbinol substituted poly(norbornene). The humidity of the sample environment was varied to determine the rate and amount of water absorbed into the photoresist thin films as a function of local environmental conditions. At 100% absolute humidity, the polymers were found to absorb 9.8, 2-3, and 5-8 wt%, respectively. The sorption and diffusion of water into the polymer thin films was observed to initially follow Fickian behavior in the low fractional mass uptake regions (M_t/M_∞<0.6), but concentration dependent diffusion behavior was seen at higher levels of water uptake. All films sorbed and desorbed water rapidly with the majority of the water uptake or loss occurring in the first few seconds of exposure.     

SrCo0.8Fe0.2O3−δ sorbent for high-temperature production of oxygen-enriched carbon dioxide stream

Perovskite-type SrCo_0.8Fe_0.2O_3−δ (SCF) has been prepared by a liquid citrate method and used to produce O₂-CO₂ gas mixture for oxyfuel combustion. Oxygen is desorbed and an oxygen-enriched carbon dioxide stream is obtained when SCF is exposed in a carbon dioxide stream at high temperature. Oxygen is adsorbed when SCF is regenerated in an air stream. A carbonation-reaction mechanism for O₂-desorption has been identified with the evidences of XRD and TGA analysis. It is found that the theoretical oxygen sorption capacity decreases with the increase of temperature. The sorption kinetics over a temperature range of 700-900 °C has been examined by TGA experiment. Both desorption and sorption processes exhibit a high reaction rate in an initial stage followed by a slower rate in a second stage. It is difficult to reach the theoretical oxygen sorption capacity during the whole temperature range due to the slow oxygen desorption rate. Optimal temperatures for oxygen sorption and desorption processes are determined to be 900 and 850 °C, respectively. Multiple sorption and desorption cycles indicate that SCF sorbent has high reactivity and cyclic stability. Comparison with the reference La_0.1Sr_0.9Co_0.5Fe_0.5O_2.6 (LSCF) and Sr_0.5Ca_0.5Co_0.5Fe_0.5O_2.47 (SCCF) sorbents shows that SCF has faster carbonation reaction at high temperature, i.e., 850 and 900 °C, and much higher theoretical oxygen sorption capacities.     

Adsorption of Some Atmospherically Important Molecules onto Large Water Clusters: SO2, SO3, HCl,and ClONO2

The adsorption of a range of atmospherically important molecules (SO₂, SO₃, HCl, and ClONO₂) on large water clusters have been studied using a supersonic molecular beam expansion to generate water clusters containing 50–450 water molecules. SO₂ and HCl were found to stick with low efficiency to the water cluster, retaining their chemical identity. In contrast, both SO₃ and ClONO₂ undergo heterogeneous reactions on the surface of the water cluster forming, respectively, H₂SO₄ and HOCl with HNO₃. For SO₃, calculations show that the large barrier that exists in the gas-phase to the reaction of SO₃ with water is removed for water clusters of a sufficient size because of stabilization of the transition state by solvation. For ClONO₂, the barrier to reaction is much larger and cannot be removed by solvation for any size cluster. In this case, it is likely that reaction takes place on the water cluster by the ionic dissociation of ClONO₂ in a similar manner to that observed for ClONO₂ on ice films.     

Sorption and transport of water vapor in glassy poly(acrylonitrile)

Sorption data for H₂O in glassy poly(acrylonitrile)(PAN) are presented for a range of relative vapor pressures at temperatures from 20 to 50°C. Simple dual mode sorption, involving “hole-filling” and molecular solution appears to dominate the low activity region of sorption. Based on the clustering analysis suggested by Zimm and Lundberg, pronounced clustering of penetrant appears to occur above a relative pressure of 0.6. The form of the effective concentration-dependent diffusion coefficient for H₂O in PAN, determined by analysis of steady state permeation data, suggests that water in the microvoids and clusters has a lower mobility than the molecularly dissolved water in the polymer matrix. Time lag measurements at high upstream relative water vapor pressures suggest that the transient state permeation has a non-Fickian character due to relaxations which occur slowly to accommodate the clustering process.     

Moisture sorption/desorption behavior of various manmade cellulosic fibers

The kinetics of dynamic water vapor sorption and desorption on viscose, modal, cotton, wool, down, and polyester fibers and lyocell knit fabrics were investigated according to the parallel exponential kinetics (PEK) model. The total equilibrium moisture regain (M_inf(total)) in all the materials decreased with increasing temperature. However, the partial equilibrium fast sorption, determined by PEK simulation at 60% relative humidity (RH) and 36°C, was larger than that at 20°C, whereas the partial equilibrium slow sorption was smaller. The characteristic times in fast sorption (τ₁) and in slow sorption (τ₂) for lyocell were reduced when the conditions were changed from 60% RH and 20°C to 36°C, whereas those for the other fibers increased. Lyocell exhibited the highest M_inf(total) value and the lowest τ₁ and τ₂ values, and this suggested high equilibrium moisture content and fast moisture uptake/release, that is, high moisture accessibility for lyocell. The relationships between the moisture regain, hysteresis, water retention capacity, and Brunauer–Emmett–Teller surface volume in the materials were also examined. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1621–1625, 2005     

Diffusion of water vapour in cellulose acetate: 2. Permeation and integral sorption kinetics

A series of permeation and integral sorption kinetic experiments were performed under both absorption and desorption conditions on membranes of cellulose acetate prepared by the same methods and conditions as before¹. Alternative methods of data treatment are presented. The slow approach to steady state as well as analysis of time lag data suggest that the limiting value of the thermodynamic permeability coefficient is approached at a slow rate. In view of a comparable time-variability already observed in the solubility coefficient¹, these results indicate that the mobility of penetrant molecules does not decrease with time; hence they imply that the effect of partial immobilisation of the water molecules in clusters is offset by polymer plastisization caused by the penetrant. The diffusion coefficient D is shown to increase with concentration in all cases, thus confirming the conclusions based on differential sorption data. D measured in absorption is, at any concentration, lower than in desorption, but in desorption it shows satisfactory agreement between the two limbs of the equilibrium isotherm.     

Effect of soil organic carbon on sorption and desorption of perchloroethylene in soils

The objective of this study was to elucidate the sorption and desorption behaviors of PCE (Perchloroethylene, C₂Cl₄) in seven soils with different organic carbon (OC) content. Sorption/desorption kinetic and serial dilution desorption experiments were conducted in batch slurries. The sorption distribution coefficient (K _d ) of PCE ranged from 0.60 to 4.66 L kg^?1. K _d tended to increase as the soil OC increased, but K _oc tended to decrease, suggesting that adsorption into the mineral surface was not negligible in soils with low OC. Desorption kinetic data were analyzed by the two-site desorption model. The sorption/desorption of PCE was not reversible over short incubation times due to the presence of a non-desorbable site. The desorbable site fractions of PCE increased and non-desorbable site fractions decreased as the soil OC increased. It is suggested that partition of PCE into soil organic carbon is more reversible than adsorption on soil minerals.     

Steady state analysis of water vapor transport in ionomers

Diffusion coefficients for water in high permeability ionomers are determined from steady state permeation measurements, corrected for boundary layer resistance and change in vapor concentration along sample length, to circumvent problems due to heat of condensation and structural relaxation. Values for water in the perfluoroionomer, Nafion, converted to solvent self-diffusion coefficients, D₁, are consistent with the NMR based free volume (fv) relation for Nafion at high concentrations. At low concentrations D₁ decreases more rapidly than fv values, an effect attributed to ion hydration involving up to 6 water molecules per sulfonate group. The reduction in D₁ due to concentration averaging in permeation, estimated using the fv relation, is about 23%. Water vapor sorption isotherms and steady state values of D₁, for two different types of styrene hydrogenated butadiene triblock ionomers and Nafion can be superimposed using morphology dependent vertical scaling factors. The simple correspondence between results for the hydrocarbon ionomers and Nafion, is attributed to a common transport mechanism based on the restriction of water to ionic pathways. There are a number of claims in the literature that water uptake by highly permeability polymers is greater from the liquid phase than from saturated vapor at unit activity. This paper demonstrates that the disparity, known as Schroeder's paradox, does not occur in sorption under equilibrium conditions or in permeability measurements, if proper corrections for boundary layer resistance and vapor concentration profile are applied.     

Stabilized Magnesium/Perfluoropolyether Nanocomposite Films by Helium Droplet Cluster Assembly

The production of stable, pre‐reactive, nanocomposite mixtures of magnesium and a perfluoropolyether (PFPE) has been achieved through the application of helium droplet cluster assembly. The nanocomposite films presented in this work demonstrated clear thermal desorption features that indicate the formation of an MgF₂ passivation layer between unreacted magnesium cores and PFPE shells upon heating. Additional heating resulted in the later rupture of the MgF₂ layer and release of trapped magnesium. The passivation behavior occurred only after deposition with the input of thermal energy, demonstrating the ability of helium droplets to assemble and deposit clusters in a pre‐reactive state.     

High temperature CO2 capture performance and kinetic analysis of Na4SiO4 ceramics

Alkali silicate-based ceramics sorbents were regarded as particularly suitable materials for CO₂ capture at high temperatures, however, the CO₂ capture behaviors of Na₄SiO₄ had been seldom investigated. In this work, the Na₄SiO₄ ceramics samples were prepared using the one-step synthesized method, and the CO₂ sorption/desorption performances at high temperatures, the thermal stability, and the cycling stability of Na₄SiO₄ were systematically investigated. It was demonstrated that the maximum CO₂ sorption capacity of SO-3 sample reached 19.4 wt% at 725 °C, and the optimal condition of cycling tests were 750 °C for sorption and 800 °C for desorption based on the sorption/desorption capacity and rate, which exhibited good thermal stability and high cyclic stability. Besides, the kinetic analysis results showed that the diffusion process was the rate-determining step of CO₂ adsorption, which was more dependent on temperature than the chemisorption process. The structure and surface morphology variations were also investigated, it was interesting that there was a special “fish scale” surface structure after the sorption process, revealing that the melting phenomenon happened during the chemisorption reaction process. By comparing with common sorbent Li₄SiO₄, the material and CO₂ capture costs of Na₄SiO₄ were much lower. These results proved that Na₄SiO₄ was expected to be a suitable high temperature CO₂ capture material as a good supplement to alkali silicate-based ceramics sorbents.     

Removal NO x from Lean Exhaust Gas by Absorption on Oxi-Anionic Materials

NO _x sorption/desorption capacities of Oxi-Anionic materials were measured under representative exhaust gas mixture conditions at 300 °C, with a NO _x trap containing CaO and CuO _x impregnated over a commercial γ-Al₂O₃. These systems absorb (or adsorb) NO _x in a gas stream containing both CO₂ at 300 °C. In the case of a thermal desorption, the trapped NO _x should desorb at a temperature below 550 °C.     

Diffusion of water vapour in cellulose acetate: 1. Differential transient sorption kinetics and equilibria

The concentration dependence of the diffusion coefficient D, of the cellulose acetate/water vapour system has been investigated: aspects of the non-Fickian behaviour of the system are reported. Kinetic and equilibrium data, were obtained for membranes of different thicknesses from a series of differential sorption experiments along both limbs of the hysteresis loop. The data are treated in alternative ways. It is concluded that we may distinguish two rate-determining molecular relaxation processes: a relatively fast one, prevailing during the initial stages of absorption, which is succeeded by a considerably slower and more drastic reorganization of the polymer structure. During the latter stage the solubility coefficient S is shown to possess a long-term time dependence, which is attributed to penetrant cluster formation. D obtained from desorption kinetics increases with concentration, whereas the apparently concentration-independent D on the absorption side is assumed to be due to partial immobilization of penetrant in regions where penetrant clusters are developed.     

Sorption of organic liquids and vapors by rigid PVC

The effects of activity and solvent strength of a number of organic penetrants upon their sorption kinetics and equilibria in poly(vinyl chloride) have been studied by gravimetric vapor and liquid sorption experiments at 30°C. For each solvent, the relation of equilibrium sorption to activity is well approximated by the Flory–Huggins equation with a characteristic value of the interaction parameter χ. The glass transition temperature T_g is depressed in direct proportion to the volume fraction of solvent absorbed; the composition corresponding to a T_g of 30°C, C_g (30°C), is in the range of 0.22–0.30 volume fraction for several common solvents. The form of the sorption kinetics varies with the ratio of the equilibrium sorption to C_g, and thus depends on the combined effects of χ, solvent activity, and plasticizing action. When the equilibrium sorption is less than about C_g/2, kinetics are Fickian, with the very low diffusivities typical of the glassy state; for sorption values between C_g/2 and C_g, anomalous kinetics are observed; and when the sorption is greater than C_g, transport in thin PVC films follows Case II kinetics. At high sorption levels, increasing film thickness produces a shift of the kinetics toward Fickian form with apparent diffusivity values typical of rubbery polymers.     

Sorption and desorption kinetics of PAHs in coastal sediment

Sorption and desorption kinetics of PAHs (naphthalene, phenanthrene and pyrene) in coastal sediment were investigated. Several kinetic models were used to analyze the kinetics: one-site mass transfer model (OSMTM), pseudo-first-order kinetic model (PFOKM), pseudo-second-order kinetic model (PSOKM), two compartment firstorder kinetic model (TCFOKM) and modified two compartment first-order kinetic model (MTCFOKM). Among the models, the MTCFOKM was the best in fitting both sorption and desorption kinetic data, and therefore could predict the most accurately. In MTCFOKM, the fast sorption fraction (f′_{1, s} ) increased with the hydrophobicity (K _ow ) of the PAHs, whereas the fast desorption fraction (f′_{1, d} ) decreased. The fast sorption rate constant (k′_{1, s} ) was much greater than the slow sorption rate constant (k′_{2, s} ). Effect of aging on the desorption kinetics was also analyzed. The f′_{1, d} in MTCFOKM decreased but the slow desorption fraction (f′_{2, d} ) increased with aging, indicating that slow desorption is directly related to aging.     

Temperature dependent adsorption of hydrogen cyanide by activated and impregnated carbons

Equilibrium adsorption—desorption data for HCN on BPL activated carbon and ASC whetlerite carbon are reported for various temperatures. W_o values calculated from the Dubinin-Polyani equation for BPL activated carbon and for ASC whetlerite carbon are 0.42 and 0.35 ml/g respectively at temperatures from 0 to 122°C. The heats of sorption were obtained from the Clausius Clapeyron equation. The heat of sorption approximates to the heat of liquefaction at high surface coverage in both carbons. Significant increases above this are observed at surface coverages below 0.3, in the case of ASC whetlerite, and below 0.05, in the case of BPL activated carbon.     

Porous calcium titanate and sorption and desorption of water under ambient conditions: a study by conventional and synchronous luminescence spectroscopy

We report chemical synthesis and characterization of micro/mesoporous CaTiO₃ by X-ray diffraction (XRD), nitrogen sorption/desorption, small angle XRD, diffuse reflectance optical spectroscopy, and luminescence spectroscopy under ambient conditions. We determined the energies of absorption and emission transitions through electronic midgap states in micro/mesoporous calcium titanate by optical spectroscopy, “conventional” photoluminescence (PL) spectroscopy and, for the first time, synchronous luminescence spectroscopy at 25?°C. Micro/mesoporous CaTiO₃ reversibly sorbs and desorbs water vapor in ambient air, with water sorption capacity being close to the total pore volume. The luminescence of micro/mesoporous CaTiO₃ in visible range at room temperature is repeatedly significantly increased upon desorption of water and decreased (quenched) upon sorption of water vapor in air, due to the interactions of the adsorbate with electronic surface midgap states.     

Unforseen factors influencing Fe(III)‐containing cations sorption on strongly basic anion exchangers

The sorption and partial destruction of the Fe(III)‐containing compounds in the aqueous medium in strongly basic anion exchangers AV‐17 and Varion‐AD phase have been investigated. It is shown that partial destruction of the Fe (III) compounds in acidulated water (pH = 2) and in K₂SO₄, Fe₂(SO₄)₃ solutions takes place. With increasing of temperature up to 50°C, the desorption degree of the iron ions from polymer phase decreases. In dried polymer, the structural and electronic state of iron compounds, according to their magnetic susceptibility, remains stable for a long time. The sorption of the Fe(III)‐containing cations at 50°C during 12 h depends essentially on the sizes of polymer granules. Sorption increases with growing of polymer granules. For comparison of sorptional capacities, the sorption of Fe(III)‐containing cations was determined on different cation and anion exchangers. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Sorption of gas condensate components by solid high-molecular-mass compounds of the gas-condensate field

The main mechanisms of sorption and desorption of saturated vapors of gas condensate fractions by asphaltenes and resins from the Orenburg oil-gas condensate field (OOGCF) was considered. These substances showed a high sorption capacity for mixtures of vaporized C₅-C₁₀ hydrocarbons in the temperature range of 50–70°C. Vapor sorption by asphaltenes is accompanied by their considerable swelling. The desorption of hydrocarbons from asphaltenes and resins proceeds much faster than their sorption. First, the lightest components (C₆ and C₇ hydrocarbons) are desorbed. Then, their relative amount in the desorbate gradually decreases while the amount of the heavier hydrocarbons octane, nonane, and decane increases. A possible mechanism of sorption of hydrocarbon vapors by asphaltenes is discussed.     

Investigation of sorption and diffusion of supercritical carbon dioxide into poly(vinyl chloride)

The interaction of supercritical carbon dioxide (scCO₂) with poly(vinyl chloride) (PVC) was systematically investigated. PVC films of 0.5 mm thickness were treated with CO₂ at pressures between 5 and 40 MPa, at temperatures between 40 and 70°C and soaking times between 0.5 and 7 h. The gravimetric desorption data were kinetically and thermodynamically evaluated assuming Fickian diffusion and the morphology changes due to the CO₂ treatment investigated by microscopic methods. The sorbed amount of CO₂, q (q=g_CO2/g_polymer) ranged between 0.03 (5 MPa, 70°C) and 0.13 (15 MPa, 40°C). The desorption diffusivities, D_d, were in the order of 0.1×10⁻¹¹ m²/s and decreased with decreasing amounts of CO₂. In contrast, the sorption diffusivities, D_s, were markedly higher and varied between 0.7×10⁻¹¹ and 2.5×10⁻¹¹ m²/s (20 MPa, 40–70°C). The CO₂ treatment changed the polymer chain structure, macroscopically visualized by the film opaqueness and by the density decrease to 1.05 g/cm³. Microcellular structures were not detected.