Molar Free Energy Of Sorption Research Articles

Determination of thermodynamic properties of poly (cyclohexyl methacrylate) by inverse gas chromatography.

In this work, some thermodynamic properties of poly (cyclohexyl methacrylate) were studied by inverse gas chromatography (IGC). For this purpose, the polymeric substance was coated on Chromosorb W and which was filled into a glass column. The retention times (t(r)) of the probes were determined from the interactions of poly (cyclohexyl methacrylate) with n-pentane, n-hexane, n-heptane, n-octane, n-decane, methanol, ethanol, 2-propanol, butanol, acetone, ethyl methyl ketone, benzene, toluene and o-xylene by IGC technique. Then, the specific volume (Vg(0)) was determined for each probe molecule. By using (1/T; lnVg(0)) graphics, the glass transition temperature of poly (cyclohexyl methacrylate) was found to be 373 K. The adsorption heat under the glass transition temperature (deltaH(a)), and partial molar heat of sorption above the glass transition (deltaH1(S)), partial molar free energy of sorption (deltaG1(S)) and partial molar entropy of sorption (deltaS1(S)) belonging to sorption for every probe were calculated. The partial molar heat of mixing at infinite dilution (deltaH1(infinity)), partial molar free energy of mixing at infinite dilution (deltaG1(infinity)), Flory-Huggins interaction parameter (chi12(infinity)) and weight fraction activity coefficient (a1/w1)(infinity) values of polymer-solute systems were calculated at different column temperatures. The solubility parameters (delta2) of the polymer were obtained by IGC technique.

Determination of Thermodynamic Properties of Poly(4-tert-Butylstyrene) by Inverse Gas Chromatography

Abstract Some thermodynamic quantities were obtained for the interactions of poly (4-tert-butylstyrene) with alcohols, ketones, acetates, aromatics and alkanes by the inverse gas chromatography method in the temperature range of 343-463 K. The specific retention volumes (Vg°), the adsorption enthalpy of probes (ΔH2), the partial molar free energy of sorption (ΔG1 S), the enthalpy of sorption (ΔH1 S), the entropy of sorption (ΔS1 S), the weight fraction activity coefficients of solute probes at infinite dilution (Ω1 ∞), and the Flory- Huggins thermodynamic interaction parameters (χ∞ 12) between polymer and solvents are given. The partial molar free energy (ΔG1 ∞, the partial molar heat of mixing (ΔH1 ∞ at infinite dilution and the solubility parameters of the polymer (δ2) were calculated. The solubility parameter of poly (4-tert-butyl- styrene) was determined from either the slope or intercept as 7.25 (cal/cm3)0,5 and 7.00 (cal/cm3)0,5 at 180°C, respectively.

Temperature changes of sorption parameters of di-n-alkylketones and methylcyclohexanones in capillary gas chromatography

The gas chromatographic behavior of di-n-alkylketones and isomeric methylcyclohexanones at variable temperatures in the isothermal runs has been studied using three capillary columns coated with SE-30, OV-225, and PEG-40M/KF stationary phases. The retention indices and their temperature increments were determined, and the partial molar free energies of the compounds under study were calculated. A linear dependence of the values of the partial molar free energy of sorption on the homologue number in di-n-alkylketones is not observed for the first member on the nonpolar SE-30 phase and for the third member on the polar OV-225 and PEG-40M/KF phases.

Sorption characteristics of polyfluorocarboxamides

The dependence of the variations in the differential molar free energy of sorption of polyfluorocarboxamides RFC(O)NR2 (RF = CF3(CF2)i,i=0 to 5, R=H or Me) on capillary columns on the molecular structure of the amides, the temperature of analysis, and the nature of the stationary phases (OV-101, XE-60, and PEG-40M) were investigated by GLC. The peculiarities of the variation of the sorption characteristics of amides in XE-60 and PEG-40M polar phases, which cause the inversion of the order of retention of the members of pseudohomologous series, were found.

The regularities of the gas-chromatographic behavior of methyl-substitutedN-alkylpiperidines

The gas-chromatographic behavior of 2-, 3-, 4-methyl- and 2,6-dimethylpiperidine bases on glass capillary columns with OV-101/KF and PEG-40M/KF at 110 °C has been studied. The contribution of a methyl group to the total molar free energy of Sorption of nonalkylated piperidine bases depends on its position in the piperidine cycle and is the least for positions 2 and 6. The variation in the retention indices of homologousN-alkylpiperidines (C1-C7) is given by a universal type of equation.

Retentions of alkylloxazoles and alkylthiazoles and their prediction based on non-linear additivity concepts in gas chromatography

The gas chromatographic (GC) behaviour of 39 alkyloxazoles and alkylthiazoles was studied on three capillary columns with OV-101-KF, Triton X-305-KF and PEG-40M-KF. The regularities in the thermodynamic characteristics of sorption of azoles having O or S atoms were established. Energy contributions of methyl, ethyl and propyl groups to the partial molar free energy of sorption of alkyloxazoles and alkylthiazoles were determined. It was found that the contributions of the same alkyl group are different and dependent on the nature of the heterocycle and the position of the alkyl group with respect to the heteroatoms in the azole ring. Two methods for the prediction of retention indices on the basis of the analogy of the GC behaviour of azoles and inconstancy of the contributions of the same alkyl groups are given. The predicted retention indices are in good agreement with the experimental values.

Comparison of methods for the determination of the polarity and selectivity of stationary phases in gas chromatography from a thermodynamic point of view

Different scales proposed for the evaluation of polarity and selectivity in gas chromatography as relative and absolute values were compared. It is shown that the scale including six parameters, Δ G( X), Δ G( Y), Δ G( Z), Δ G( U), Δ G( S), and Δ G(CH 2), is more suitable and allows a unified system to be obtained for the polarity and selectivity of conventional stationary phases, organic and inorganic salts and polymer sorbents. The main equation for the calculation of the partial molar free energy of sorption, Δ G, is simplified for capillary gas chromatography.

Calculation of the thermondynamic values of alkylthiazoles from the Kovats retention indices on the basis of the non-linear additivity principle

Retention indices and their energy equivalents were determined for ten alkylthiazoles analysed on the stationary phases Apiezon L, Triton X-305 and Carbowax 1000. It was found that the energy contributions of identical alkyl groups to the partial molar free energy of sorption of a molecule are not equivalent. Smaller energy contribututions are due to the α-position of alkyl groups with respect to the heteroatoms in the thiazole ring (α-effect). This effect was most pronounced for 2-alkylthiazoles. Higher sorption energies were found for dimethylthiazoles with two methylgroups in a vicinal position. The retention indices were predicted for ten other di- and tri-substituted methyl, ethyl and propyl thiazoles on the basis of the so-called α- and ortho-effects. The predicted values are in good agreement with the experimentally determined values.

Thermodynamic distinction in donor-acceptor interactions of organic bases with KF and Na 3PO 4 on hydrogenated apiezon columns

The retention indices, I, and the partial molar free energies of sorption, Δ G, have been determined for n-alkanes, aromatic hydrocarbons, aliphatic and aromatic amines and pyridine on three columns with hydrogenated Apiezon L containing equimolar quantities of KOH, KF and Na 3PO 4. It is shown that neither I nor ΔG of n-alkanes and aromatic hydrocarbons depends on the support treatment. The differences in the abilities of organic bases to undergo donor—acceptor interactions with KOH, KF and Na 3PO 4 under the conditions prevalent in gas chromatography have been estimated thermodynamically. It is shown that the contribution of the donor—acceptor interaction energy to the total partial molar free energy of sorption is the same for KOH and KF, but is higher for Na 3PO 4 and dependent on the type of organic base.

Change in the differential molar free energy of sorption of a methylene group as a function of the length of the chain of an n-alkane under the conditions of GC analysis

1. A law of the change in the differential molar free energy of sorption of n-alkanes as a function of the length of the chain, the polarity of the stationary phase (SP), and the temperature of analysis has been found. 2. The energy contribution of a methylene unit of an n-alkane changes hyperbolically with the chain length, rising to the first members of the series. The greatest contribution to the free energy of sorption of an n-alkane is made by the α-methylene unit, and then by the β- and γ-methylene units. 3. An equation has been proposed which permits the calculation of\(\Delta G_{n,av}^{CH_2 }\), the coefficients of which depend on the SP and the temperature of analysis. The energy contribution of each methylene unit in the interval studied depends linearly on the temperature.

Analysis of polar compounds on polyethylene glycol glass capillary columns : The influence of KF and Na 3PO 4 on the change in partial molar free energy

The effect of treating the glass column surface in capillary chromatography with KF and Na 3PO 4 on the retention of polar and non-polar compounds has been investigated. Aliphatic hydrocarbons, benzene, toluene, nitrobenzene, pyridine and polar derivatives of octaine with such functional groups as -NH 2, -OH, -SH, -Br and = C = O have been analyzed using PEG-40M, PEG-40M + KF and PEG-40M + Na 3PO 4 glass capillary columns. The energy contributions of functional groups to partial molar free energy of sorption of octane derivatives on these three columns were calculated. The increase of the energy contributions of proton donor functional groups -NH 2, =NH, -OH for the PEG +KF system was observed and explained by hydrogen bonding with KF taking part as a base in the chromatographic separation.

Effect of KF and NA3PO4 on the change in differential molar free energy of sorption of polar substances during analysis in glass capillary columns with polyethylene glycol

1. The change in the energy contribution of the functional groups OH, NH2, NH, SH, Br, and C =O in a series of octane derivatives was studied by chromatography in glass capillary columns with polyethylene gly-col-40M after treatment with KF and Na3PO4. 2. The increase which we observed in the energy contributions of the functional groups which are hydrogen donors when analyzed on PEG in the presence of KF is attributed to their ability to form a hydrogen bond with the salt, the anion acting as a base. 3. We studied the effect of KF and Na3PO4 on the change in the energy contributions of the aromatic compounds toluene, nitrobenzene, and pyridine, compared to that of benzene. In the energy of sorption of pyridine, as well as a tertiary amine, it is probable that electrostatic interaction with the salts' metal ions makes a contribution. 4. In the analysis of n-alkanes on PEG, the differential molar free energy of solution due to the methylene group (ΔGCH2) in unchanged in the presence of KF and Na3PO4.