Molar Enthalpy Of Sorption Research Articles

Investigation of sorption and diffusion of hydrocarbons into polydimethylsiloxane in the headspace-solid phase microextraction sampling process via inverse gas chromatography

Inverse gas chromatography was employed to investigate the sorption and diffusion of hydrocarbons into polydimethylsiloxane (PDMS) in the headspace-solid phase microextraction (HS-SPME) sampling process. Six hydrocarbons as molecular probes and two types of non-cross-linked PDMS with different average molecular weights as stationary phases were used in this study. Experimental measurements with columns containing a PDMS stationary phase were carried out to obtain specific retention volumes, molar enthalpies of sorption, interaction parameters, diffusion coefficients, and activation energies of diffusion of hydrocarbon probes over temperatures ranging from 60 to 90°C. The primary driving force of the hydrocarbon sorption into the PDMS SPME fibers was found to be the molar enthalpy of sorption, which depended on the molecular size of the hydrocarbons. As the molecular size of the hydrocarbon increased, the molar enthalpies of sorption became more exothermic. Interaction parameters and diffusion coefficients indicated that both n-heptane and n-octane were diffused into the PDMS matrix and localized to form clusters or aggregates, which were responsible for more negative molar entropies of sorption. However, the diffusivities of n-nonane and aromatic probes were limited due to their large molecular size and lack in the structural flexibility, respectively. The molar enthalpies of hydrocarbon sorption were independent of the average molecular weight of PDMS. However, specific retention volumes, interaction parameters, diffusion coefficients, and activation energies of diffusion of the hydrocarbons depended on the molecular weight of PDMS as well as the molecular weights and structures of hydrocarbons, as shown by the results of the Wilcoxon signed-rank test.

Determination of the thermodynamic parameters of ionic liquid 1-hexyl-3-methylimidazolium chloride by inverse gas chromatography

Some thermodynamic properties for the ionic liquid 1-hexyl-3-methylimidazolium chloride ([HMIM]Cl) were investigated by inverse gas chromatography (IGC) method at temperatures from 343.15K to 373.15K. The thermodynamic parameters, including weight fraction activity coefficient, Flory–Huggins interaction parameter, partial molar enthalpy of mixing, molar enthalpy of sorption, activity coefficient at infinite dilution and solubility parameter, were obtained to judge the interactions between [HMIM]Cl and the selected solvents at the studied temperatures. The results showed that dichloromethane, chloroform, carbon tetrachloride, ethanol, and carbinol were the favorite solvents for [HMIM]Cl, while n-C6 to n-C9, cyclohexane, benzene, toluene, m-xylene, acetone, ethyl acetate, tetrahydrofuran, ether, methyl, and acetate were bad solvents for [HMIM]Cl.

Determination of the solubility parameter of organosolv lignin by inverse gas chromatography

An inverse gas chromatographic (IGC) method has been used to measure the solubility parameters (delta2) of organosolv lignin at the absolute temperatures from 333.15 K to 373.15 K. The test probe solvents were n-octane (n-C8), n-decane (n-C10), n-dodecane (n-C12), and n-tetradecane (n-C14). The specific retention volumes of the solvents (Vg0), the molar enthalpy of sorption (deltaH1S), the partial molar enthalpy of mixing at infinite dilution (deltaH1infinity), the molar enthalpy of vaporization (deltaHv), the activity coefficients at infinite dilution (Omega1- infinity), and Flory-Huggins inter action parameters (chi12infinity) between organosolv lignin and probe solvents were obtained. The results showed that the above four probes are poor solvents for organosolv lignin; at the same temperature, the chi12infinity reduced with the increase of the carbon number of probe solvents. The average solubility parameter of organosolv lignin was determined as 19.03 (J x cm(-3))1/2.

Determination of thermodynamic parameters for ionic liquid 1-hexyl-3-methylimidazolium trifluoromethansulfonate by inverse gas chromatography

The thermodynamic parameters of ionic liquid 1-hexyl-3-methylimidazolium trifluoromethansulfonate ([HMIM] OTF) were investigated by inverse gas chromatography in the temperature range of 343.15-373.15 K. Eighteen probe solvents were used to calculate the molar enthalpy of sorption, molar enthalpy of mixing at infinite dilution, molar enthalpy of vaporization and the mass fraction activity coefficients. Furthermore, Flory-Huggins interaction parameters, the solubility parameter of the ionic liquid were calculated to judge the interactions between [HMIM] OTF and the 18 probes solvents. The results showed that among the selected solvents, n-C6-9, tetrahydrofuran, diethyl ether, cyclohexane and benzene are the poor solvents for [HMIM] OTF, while dichloromethane, acetone, chloroform, ethyl acetate, carbon tetrachloride, methyl acetate, toluene and methanol are the favorite solvents for [HMIM] OTF. In addition, the solubility parameter of [HMIM] OTF at room temperature (298.15 K), which was obtained by linear extrapolation method, was 20.74 (J/cm3)0.5. This study could be used as a reference to the application and research of the ionic liquids.

Measurements of water sorption enthalpy on polymer surfaces and its effect on protein adsorption

The molar enthalpy of sorption ( ΔH m s` ) of water vapor onto three polymer surfaces and its effect on nonspecific protein adsorption were investigated by inverse gas chromatography (IGC). The values of ΔH m s measured by IGC were found to be −16.9 ± 1.2, −18.6 ± 1.3, and −29.9 ± 2.4 kJ/mole for polystyrene (PS), polymethylmethacrylate (PMMA), and poly(2-hydroxyethyl methacrylate) (PHEMA), respectively, over a temperature range of 333–423 K. Protein adsorption to three polymer-coated substrates was conducted as a function of the bulk protein concentration using lysozyme, fibrinogen, and bovine serum albumin (BSA), and the amount of adsorbed protein was measured by the solution depletion method. For a given bulk protein concentration, a larger amount of protein is adsorbed on PS and PMMA surfaces which have greater ΔH m s than that of PHEMA surfaces. Although ΔH m s for PS and PMMA are close to each other, PS surfaces were found to exhibit a higher adsorption affinity than PMMA surfaces over the proteins and concentrations investigated. Our results indicate that the strength of water–polymer interactions and the functional groups on the polymer surface are important factors for controlling the amount of nonspecifically adsorbed protein.

Thermodynamic Properties of Hyperbranched Polymer, Boltorn U3000, Using Inverse Gas Chromatography

Mass-fraction activity coefficients at infinite dilution (Omega13(infinity)) of alkanes (C5-C10), cycloalkanes (C5-C8), alkenes (C5-C8), alkynes (C5-C8), aromatic hydrocarbons (benzene, toluene, ethylbenzene, o-, m-, p-xylene, thiophene), alcohols (C1-C5), water, ethers (tetrahydrofuran (THF), methyl-tert-butylether (MTBE), diethyl-, di-n-propyl-, di-n-butyl ether), and ketones (propanone, 2-pentanone, 3-pentanone, 2-hexanone, 3-hexanone, cyclopentanone) in the hyperbranched polymer, Boltorn U3000 (B-U3000), have been determined by inverse gas chromatography (IGC) using the polymer as the stationary phase. The measurements were carried out at different temperatures between 308.15 and 348.15 K. The density and thermophysical properties of polymer were described. The specific retention volume (V(g)), the Flory-Huggins interaction parameter (chi13(infinity)), the molar enthalpy of sorption (the partial molar enthalpies of solute dissolution) (Delta(s)H), the partial molar excess enthalpy at infinite dilution of the solute and polymer (DeltaH1(E,infinity)), the partial molar Gibbs excess energy at infinite dilution (DeltaG1(E,infinity)), and the solubility parameter (delta3) were calculated.

Measurements of mass-fraction activity coefficient at infinite dilution of aliphatic and aromatic hydrocarbons, thiophene, alcohols, water, ethers, and ketones in hyperbranched polymer, Boltorn H2004, using inverse gas chromatography

Thermodynamic properties of the hyperbranched polymer, Boltorn H2004 (B-H2004), were investigated by inverse gas chromatography with 42 different solvents: n-alkanes (C 5–C 10), cycloalkanes (C 5–C 8), alkenes (C 5–C 8), alkynes (C 5–C 8), aromatic hydrocarbons (benzene, toluene, ethylbenzene, o-, m-, p-xylene, thiophene), alcohols (C 1–C 5), water, ethers (tetrahydrofuran (THF), methyl- tert-butylether (MTBE), diethyl-, di- n-propyl-, di- n-butyl ether), and ketones (acetone, 2-pentanone, 3-pentanone, 2-hexanone, 3-hexanone, cyclopentanone) at the temperatures from (308.15 to 348.15) K using the inverse gas chromatography (IGC). The density and thermophysical properties of polymer were described. The specific retention volume ( V g ), the mass-fraction activity coefficient at infinite dilution ( Ω 13 ∞ ) , the Flory–Huggins interaction parameter ( χ 13 ∞ ) , the molar enthalpy of sorption in the polymer ( Δ s H ) , the partial molar excess enthalpy at infinite dilution ( Δ H 1 E , ∞ ) , the molar enthalpy of vaporization to the ideal-gas state for the pure solutes ( Δ vap H 0 ) , the partial molar Gibbs excess energy at infinite dilution ( Δ G 1 E , ∞ ) , and the solubility parameter of the polymer ( δ 3), were calculated. The UNIFAC-FV model was used to predict the mass-fraction activity coefficient at infinite dilution for different solutes in the B-H2004 polymer.

Thermodynamics of Nafion™–vapor interactions. I. Water vapor

Interaction between water vapor and Nafion™ perfluorosulfonate ionomer has been investigated via combined flow microcalorimetry and isothermal sorption over a wide range of water relative pressure. The molar enthalpy of sorption was determined for the untreated polymer, the residual polymer after extraction by aqueous propanol, and the extracted fraction. The extract appears to be low molecular weight Nafion™ but with an equivalent weight more than double that of the unextracted polymer. The equivalent weight of the residual polymer is slightly lower than that of the original Nafion™, apparently due to partial alkylation. Molar enthalpy for formation of the sulfonic acid monohydrate is about the same for the residual and unextracted polymers, but much greater for the extracted fraction. For untreated Nafion™, the magnitude and concentration dependence of the molar enthalpy indicates that sorption of water exhibits a clear progression from hydronium ion formation (≤1 H 2O/SO 3H) through growth of isolated hydrated clusters (≤6 H 2O/SO 3H) to a continuous internal water phase. A more complicated process occurs for the extract and residual polymer fractions in that an endotherm associated with elastic compression of the polymer matrix surrounding isolated water clusters is superimposed on the hydration exotherm over the concentration range of cluster growth. There is only a minor indication of this endotherm for unextracted Nafion™ because of more facile relaxation of the polymer structure due to plasticization by the low molecular weight fraction.

Thermodynamic interactions and characterization of poly( p-chlorostyrene) with some aliphatic and aromatic probes by inverse gas chromatography

Some thermodynamic quantities were obtained for the interactions of poly( p-chlorostyrene) with n-pentane, n-hexane, n-heptane, benzene, toluene, isopropylbenzene and n-propylbenzene by the inverse gas chromatography method in the temperature range 150–170°C. The specific retention volumes ( V 0 g), weight fraction activity coefficients of solute probes at infinite dilution ( Ω ∞ 1 ), Flory-Huggins thermodynamic interaction parameters ( χ ∞ 12), interaction parameters based on hard-core volumes ( χ∗ 12 ), effective exchange interaction parameters ( X 12) of the equation of state theory, between polymer and solutes are given. The molar enthalpy of sorption ( Δ H ̄ s ), the partial molar heat of mixing at infinite dilution ( Δ H ̄ ∞ 1 ) and the solubility parameter of polymer ( γ 2) were also calculated.