Sorption isotherms, sorption enthalpies, diffusion coefficients and permeabilities of water in a multilayer PEO/PAA polymer film using the quartz crystal microbalance/heat conduction calorimeter

Sorption isotherms, sorption enthalpies, and diffusion coefficients for water in an 11 μm thick PEO/PAA multi-layer film have been measured at 30, 40, and 60 °C for relative humidities between 0 and 70%. All quantities were measured on the same film using the quartz crystal microbalance/heat conduction calorimeter. Water diffusion coefficients in the film are several orders of magnitude lower than in the separate components. Sorption isotherms are of type III at 30 and 40 °C and linear at 60 °C. Water vapor permeabilities are calculated as the product of Henry's law solubility and diffusion coefficient. The permeability of the PEO/PAA multilayer film is exceedingly low compared to other polymer films used as membranes. The enthalpy of water sorption determined from the sorption isotherms using the van’t Hoff relation is 32.9 ± 0.3 kJ/mol. Calorimetric enthalpies of water sorption range from 42 to 34 kJ/mol at 30 and 40 °C over the humidity range studied. The change in motional resistance, a quantity proportion to the loss compliance of the film, has also been recorded at all three temperatures, and a common trend is an increase in loss compliance with increasing relative humidity, indicating plasticization of the film by water.     

Comparative adsorption studies of indigo carmine dye on chitin and chitosan

The adsorption of indigo carmine dye onto chitin and chitosan from aqueous solutions was followed in a batch system. The ability of these materials to adsorb indigo carmine dye from aqueous solution was followed through a series of adsorption isotherms adjusted to a modified Langmuir equation. The maximum number of moles adsorbed was 1.24 +/- 0.16 x 10(-5) and 1.54 +/- 0.03 x 10(-4) mol g(-1) for chitin and chitosan, respectively. The same interactions were calorimetrically followed and the thermodynamic data showed exothermic enthalpic values of -40.12 +/- 3.52 and -29.25 +/- 1.93 kJ mol(-1) for chitin and chitosan, respectively. Gibbs free energies for the two adsorption processes of indigo carmine dye presented a positive value for chitin and a negative one for chitosan, reflecting that dye/surface interactions are thermodynamic favorable for chitosan and nonspontaneous for chitin at 298.15 K. The interaction processes were accompanied by an increase of entropy value for chitosan (90 +/- 6 J mol(-1)K(-1)) and a decrease for chitin (-145 +/- 13 J mol(-1)K(-1)). Thus, dye/chitosan interaction showed favorable enthalpic and entropic processes, reflecting thermodynamic stability of the formed complex, while dye/chitin interaction showed an exothermic enthalpic value and a highly nonfavorable entropic effect, resulting in a nonspontaneous thermodynamic system.     

Kinetic and equilibrium characteristics of sorption of saponin of <Emphasis Type="Italic">Quillaja Saponaria Molina</Emphasis> on chitosan

The equilibrium and kinetic curves of the sorption of saponin of Quillaja saponaria molina on chitosan were analyzed. The inner diffusion was found to be limiting, and its coefficients were calculated. It was found that the form of the curves of the sorption isotherms of saponin is determined by the competing processes of association in solution and absorption by chitosan.     

改性土壤对水中苄黄隆的吸附行为研究

研究了季铵盐阳离子表面活性荆四甲基铵离子(TMA)和十六烷基三甲基铵离子(HDTMA)改性的黄土l,黄土2，沉积物对水中苄黄隆的吸附作用．结果表明：改性后土壤对苄黄隆的吸附能力提高．同时考察了改性土壤对苄黄隆吸附的热力学行为．结果表明：HDTMA改性的土壤对苄黄隆的吸附等温线为线性，吸附类型以分配为主．HDTMA改性黄土1吸附热为-6．12kJ/mol，HDTMA改性黄土2的吸附热为-8．44kJ/mol。HDTMA改性沉积物的吸附热为-4．04kJ／mol．结合力以疏水作用力为主：TMA改性的土壤对苄黄隆的吸附等温线符合Freundlich方程．考察了溶液pH对吸附量的影响．结果表明在酸性条件下．改性土壤的吸附能力较大．     

Calorimetric studies of the association of chitin and chitosan with sodium dodecyl sulfate

The interaction of hydrophobic chitin and chitosan with sodium dodecyl sulfate (SDS) has been studied by titration calorimetry at 298.15K. The nature of interaction of the surfactant and biopolymers was followed by enthalpy interaction profiles. The mixing enthalpy curves were determined by mixing SDS solutions above their critical micelle concentration with chitin and chitosan suspensions in different concentrations. The Gibbs free energy of aggregation values were -23.21, -22.71 and -21.53 kJ mol(-1) for chitin in 0.02, 0.05 and 0.1% concentration, respectively, and 28.30, 24.38 and 24.20 kJ mol(-1) for chitosan in 0.02, 0.05 and 0.1% concentration, respectively. The critical aggregation concentration (cac) obtained by calorimetric data gave 6.32, 7.07 and 9.14 mmol kg(-1) in 0.02, 0.05 and 0.1% concentration, respectively, for chitin and 2.09, 4.91 and 5.11 mmol kg(-1) for chitosan in 0.02, 0.05 and 0.1% concentration, respectively.     

SORPTION OF PHENOL ONTO GEL—TYPE CROSSLINKED POLYSTYRENEISOCYANURIC ACID RESIN

Spherical crosslinked polystyrene-isocyanuric acid resin was synthesized by reaction of chloromethylated polystryene with isocyanuric acid.The sorption isotherms of phenol from aqueous solution and cyclohexane solution onto the resin were measured.It is of interest to notice that the resin sorbed phenol efficiently though its specific surface area was 0 and did not swell in water,and the sorption capactity from aqueous solution was close to that of phenol onto XAD-4 at the same equilibrium concentration.Sorption enthalpies calculated from the isotherms according to the Clausius-Clapeyron equation were -21-25kJ/mol and -39-41kJ/mol respectively.These values impled that the sorption processes were based on hydrogen bonding.In addition.the details of the hydrogen bonding between the active sites of the resin and phenol were suggested.     

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     

Polyimide-epoxy alloys prepared via micro-modification: Water sorption and diffusion

A novel polyimide-epoxy or PI-EP alloys are prepared by the modification of polyamic acid in the concentration range of 1.54×10⁻⁶ to 1.54×10⁻² mol/L. The methanol sorption for these alloys at 24 hrs and at equilibrium conditions are determined and the residual solvent in fully cyclized polyimides were calculated. The presence of the residual solvent is visualized in fully imidized polymer and a structure containing partly imidized amic acid moiety is proposed and their concentration (in percentage) is calculated. The water sorption for these alloys at 24 hrs and at equilibrium conditions and the values of the water diffusion coefficient are determined from absorption isotherms. The PI-EP alloys have shown comparatively lower water sorption and higher diffusion coefficient than the unmodified polyimide. The mechanistic aspects of water sorption and diffusion are discussed.     

Sorption of Na+, Ca2+ ions from aqueous solution onto unbleached kraft fibers-kinetics and equilibrium studies

The sorption of Na+ and Ca2+ from aqueous solutions onto unbleached kraft fiber was investigated. The sorption kinetics was found to be highly dependent on pH, initial concentration, and temperature. The sorption rate increased as the initial concentration and pH were increased. Thermodynamic and kinetic results indicated that the sorption of Na+ and Ca2+ onto kraft fiber was exothermic, reversible, and spontaneous with activation energies of 11.0 and 23.3 kJ/mol, respectively. The sorption kinetics followed a pseudo-second-order model and the equilibrium data followed the Langmuir isotherms. The fiber sorption capacities calculated from the Langmuir isotherms were similar to the fiber charges determined by potentiometric titration at pH > 7.     

Selective Water Sorbents for Multiple Applications. 11. CaCl2 Confined to Expanded Vermiculite

This paper presents the water sorption properties of a new selective water sorbent based on expanded vermiculite as a host matrix and calcium chloride as a hygroscopic salt. Sorption isobars, isosters and isotherms at T = 30–150°C and vapor partial pressure 8.2–42.0 mbar clearly show that at low water contents crystalline hydrates with 0.33, 1 and 2 molecules of water per 1 molecule of CaCl₂ are formed in the pores. These hydrates are stable over a temperature change of 20–30°C and exhibit kinetically slow transformations. At higher water uptake, the vapor absorption leads to the formation of a CaCl₂ aqueous solution inside the pores, which properties are close to those in the bulk. Isosteric sorption heat was found to depend on water sorption and change from 76.3 kJ/mol for solid hydrates to 39.1–46.6 kJ/mol.     

Sorption and transport of water in nylon-6 films

Sorption and transport properties of water through films of Nylon-6 were obtained at 5, 23, and 40°C. Commercially available films were used and a Cahn electrobalance was employed for measuring the water uptake by the polymer samples. Values of the water sorption isotherms are accurately described by the Langmuir/Flory-Huggins dual-mode sorption model. At water activity values below 0.15, the volume fraction of water described by the Langmuir portion of the model was greater than the Flory-Huggins population. Solubility and diffusion coefficients of water, as well as the diffusion activation energy and enthalpy of dissolution of water for Nylon-6, were determined from the sorption experiments. Values obtained support the hypothesis of a bimodal water sorption mode, and the formation of water clusters. © 1994 John Wiley & Sons, Inc.     

Selective water sorbents for multiple applications, 1. CaCl2 confined in mesopores of silica gel: Sorption properties

This paper presents sorption properties of a selective water sorbent based on mesoporous KSKG silica gel as a host matrix and calcium chloride as a hygroscopic salt. Sorption isobars, isochores and isotherms at T=20–150°C and vapor partial pressures of 8–133 mbar clearly showed two types of water sorption: 1) the formation of solid crystal hydrates at low amounts N of sorbed water, and 2) vapor absorption mainly by the salt solution at higher N. Sorption properties of CaCl₂ crystal hydrates were found to change strongly due to their impregnation into mesoporous silica gel, whereas the solution confinement to the mesopores did not change its water sorption properties with respect to the bulk solution. Isosteric sorption heat was measured to depend on water sorption and to change from 62.5 kJ/mol for solid hydrates to 42.2–45.6 kJ/mol for solution.     

The solubility and diffusion of water in poly(aryl-ether-ether-ketone) (PEEK)

The transport properties of water in neat poly(aryl-ether-ether-ketone) (PEEK) coupons (2 to 6 mm thick) were investigated by gravimetric and mass spectrometric methods. The solubility of water increases from 0.44 wt.% at 35°C to 0.55 wt.% at 95°C; the temperature coefficient is 8 kJ/mol (1.9 kcal/mol). The diffusion processes for sorption, desorption, and resorption at 35°, 50°, 65°, 80°, and 95°C are, within experimental error, the same. The activation energy for diffusion is 42.7 kJ/mol (10.2 kcal/mol). The diffusion process is classical Case I Fickian in the temperature region investigated.     

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     

SORPTION OF PHENOL ONTO GEL-TYPE CROSSLINKED POLYSTYRENEISOCYANURIC ACID RESIN

I INTRODUCTIONIn our previous work, three series of macroporous hydrogen-bonding adsorbents have beenstudied, which were adsorbents with hydrogen donator, adsorbents with hydrogen acceptor, andadsorbents with both hydrogen donator and acceptor if-31. If a gel-type resin with hydrogendonator and/or acceptor contacts with a compound with hydrogen acceptor and/Or donatof, canthe gel-type resin sorb the compound based on of hydrogen bonding? Here we report the sorptionof phenol onto gel-type …     

Saturation of hydrogen sorption in Zn benzenedicarboxylate and Zn naphthalenedicarboxylate

We report excess hydrogen saturation values from high-pressure isotherms of metal organic framework structures taken at 77 K. Zn benzendicarboxylate (IRMOF-1) and Zn naphthalendicarboxylate (IRMOF-8) linker structures show identical saturation values of 137 hydrogen molecules on a per unit cell basis, despite the higher sorption potential of IRMOF-8 of 6.1 kJ/mol over that of IRMOF-1 of 4.1 kJ/mol. Charge transfer between linker and vertex, as well as surface area, appear to dominate the sorption behavior, over that of linker length in these two systems.     

Study of Water Adsorption on Activated Carbons with Different Degrees of Surface Oxidation

A carbon of wood origin was oxidized with different oxidizing agents (nitric acid, hydrogen peroxide, and ammonium persulfate). The microstructural properties of the starting material and the oxidized samples were characterized using sorption of nitrogen. The surface acidity was determined using Boehm titration and potentiometric titration. The changes in the surface chemistry were also studied by diffuse reflectance FTIR. Water adsorption isotherms were measured at three different temperatures close to ambient (relative pressure from 0.001 to 0.3). From the isotherms the heats of adsorption were calculated using a virial equation. The results indicated that the isosteric heats of water adsorption are affected by the surface heterogeneity only at low surface coverage. In all cases the limiting heat of adsorption was equal to the heat of water condensation (45 kJ/mol).     

Determining the effects of vapor sorption in polymers with the quartz crystal microbalance/heat conduction calorimeter

The quartz crystal microbalance/heat conduction calorimeter (QCM/HCC) is a versatile instrument coupling both gravimetric and calorimetric techniques. The QCM/HCC is used to probe vapor sorption in thin films. Three parameters are measured simultaneously as a thin film undergoes vapor sorption, namely: mass changes in the film (±10 ng), corresponding thermal effects upon vapor sorption (±100 nW), and motional resistance (±0.5Ω) changes within the film. A range of film thicknesses (0.75 to 8.5 μm) of the polymer, Tecoflex? are cast on QCMs and the interaction of each film with ethanol and water is determined. From the direct calorimetric measurements, sorption enthalpies (Δ_sorptionH kJ/mol) are determined for the film–vapor interactions. Sorption isotherms are then analyzed for each film. The isotherms shown here generally display a linear Henry's Law dissolution relationship between the vapor pressure and the amount of vapor sorbed into the film. Motional resistance data provides a window to view viscoelastic effects of the polymer films upon vapor sorption. Motional resistance data are compared for ethanol sorption in a relatively thin (0.75 μm) and thicker (8.5 μm) Tecoflex? film. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3893–3906, 2004     

Sorption of traces of silver ions onto polyurethane foam from acidic solution

The sorption of traces of silver ions onto polyurethane foam (PUF) has been investigated in detail. Maximum sorption of silver (K(d)=6109 cm(3) g(-1), %sorption>97.5%) has been achieved from 1 M nitric acid solution after equilibrating silver ions with approximately 29 mg PUF for 20 min. The kinetics and thermodynamics of the sorption of silver ions onto PUF have also been studied. The sorption of silver ions onto PUF follows a first-order rate equation, which results as 0.177 min(-1). The variation of sorption with temperature yields the values of DeltaH=-56.1+/-3.2 kJ mol(-1), DeltaS=-159.7+/-10.5 J mol(-1) K(-1) and DeltaG=-8.68+/-0.09 kJ mol(-1) at 298 K with a correlation factor gamma=0.9919. The sorption data were subjected to different sorption isotherms. The sorption follows Langmuir, Freundlich and Dubinin-Radushkevich (D-R) isotherms. The values of Langmuir isotherms Q=65.4+/-1.5 mumol g(-1) and b=(4.79+/-1.16)x10(4) dm(3) mol(-1) have been evaluated for Langmuir sorption constants, whereas the Freundlich sorption isotherm gives the value 1/n=0.12+/-0.02 and A=0.15+/-0.03 mmol g(-1). The D-R parameters computed were beta=-0.000817+/-0.000206 mol(2) kJ(-2), X(m)=76.8+/-8.7 mumol g(-1) and E=24.7+/-3.2 kJ mol(-1). The influence of common ions on the sorption was also examined. It is observed that Hg(II), thiourea, Al(III), thiocyanate and thiosulphate reduce the sorption, whereas Cu(II), citrate and acetate ions enhance the sorption significantly. It can be concluded that PUF may be used to remove traces of silver ions from its very dilute solutions or for its preconcentration from aqueous acidic solutions.     

Sorption of methanol/MTBE and diffusion of methanol in 6FDA–ODA polyimide

This article discusses the diffusion and solubility behavior of methanol/methyl tert‐butyl ether (MTBE) in glassy 6FDA–ODA polyimide prepared from hexafluoroisopropylidene 2,2‐bis(phthalic anhydride) (6FDA) and oxydianiline (ODA). The diffusion coefficients and sorption isotherm of methanol vapor in 6FDA–ODA polyimide at various pressures and film thicknesses were obtained with a McBain‐type vapor sorption apparatus. Methanol/MTBE mixed‐liquid sorption isotherms were obtained by head‐space chromatography and compared with a pure methanol sorption isotherm obtained with a quartz spring balance. Methanol sorption isotherms obtained with the two methods were almost identical. Both methanol sorption isotherms obeyed the dual‐mode model at a lower activity, which is typical for glassy polymer behavior. The MTBE was readily sorbed into the polymer in the presence of methanol, but the MTBE sorption isotherm exhibited a highly nonideal behavior. The MTBE sorption levels were a strong function of the methanol sorption level. Methanol diffusion in the polymer was analyzed in terms of the partial immobilization model with model parameters obtained from average diffusion coefficients and the dual‐mode sorption parameters. Simple average diffusion coefficients were obtained from sorption kinetics experiments, whereas the dual‐mode sorption parameters were obtained from equilibrium methanol sorption experiments. An analysis of the mobility and solubility data for methanol indicated that methanol tends to form clusters at higher sorption levels. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2254–2267, 2000