Ozlem Cankurtaran

Comparison of the intrinsic viscosity and inverse gas chromatography techniques in determination of the exchange enthalpy and entropy parameters

Abstract The χ 1 -interaction parameters of poly(dimethyl siloxane) with methyl ethyl ketone at very low polymer concentration were determined by means of intrinsic viscosity (IV) measurements at several temperatures. The χ t ∞ -total interaction parameters of the same system at infinitely high polymer concentration were also determined using inverse gas chromatography (i.g.c.) technique around the same temperature range. Then, exchange enthalpy, X 12 , and entropy, Q 12 , parameters in the Florys equation of state theory were determined from the obtained interaction parameters. Both X 12 and Q 12 parameters obtained by IV are lower than those found by i.g.c..

Determination of exchange enthalpy and entropy parameters of poly(dimethyl siloxane) with some n‐alkanes by inverse gas chromatography

The total interaction parameter at infinitely high polymer concentration, χ t ∞, and the effective exchange energy parameter, X 12 , of poly(dimethyl siloxane) with n-pentane, n-hexane, n-heptane and n-nonane were determined around room temperature using the inverse gas chromatography technique. The values of χ t ∞ are in agreement with corresponding literature values. The exchange enthalpy X 12 and entropy, Q 12 , parameters were determined at the same temperature. The X 12 parameters increase with the carbon number of the n-alkanes, while their temperature dependence is almost negligible. The Q 12 parameters are approximately independent of temperature and carbon number of the n-alkanes.

Determination of the exchange enthalpy and entropy parameters of the equation-of-state theory for poly(dimethyl siloxane) in various solvents

Abstract The interaction parameter χt∝ and the effective exchange energy parameter X 12 at infinite dilution of cyclohexane, benzene and chlorobenzene with poly(dimethyl siloxane) were determined around room temperature, according to relations given in the Flory formulation of the equation-of-state theory using the inverse gas chromatography technique. Then, the exchange enthalpy X12 and entropy Q12 parameters were determined by using a relation for the enthalpy interaction parameter χh of the equation-of-state theory, which is arranged for the inverse gas chromatography conditions. The values of the above-mentioned parameters are comparable with the values obtained earlier with other methods. The X12 and Q12 parameters of cyclohexane increase slightly with temperature, while those of benzene and chlorobenzene are almost independent of temperature.

Investigation of thermodynamic and surface characterisation of 4-[4-(2-ethylhexyloxy)benzoyloxy]benzoic acid thermotropic liquid crystal by inverse gas chromatography

The inverse gas chromatography method was used to obtain thermodynamic and surface properties of the thermotropic liquid crystalline material, 4-[4-(2-ethylhexyloxy)benzoyloxy]benzoic acid (EBBA). The retention diagrams of undecane, dodecane, tridecane, ethyl acetate, n-butyl acetate, iso-butyl acetate, toluene, ethylbenzene, iso-propylbenzene, n-propylbenzene and chlorobenzene on EBBA were plotted at temperatures between 443.2 and 468.2 K. The specific retention volume, , Flory–Huggins interaction parameter, , equation-of-state interaction parameter, , and effective exchange energy parameter, , were determined. The dispersive component of the surface free energy, , of the studied adsorbent surface was estimated using retention times of different nonpolar organic solvents in the infinite dilution region. The specific free energy of adsorption, the enthalpy of adsorption, , and the entropy of adsorption, , of solvents on liquid crystal were determined. The values of were correlated with the donor and the acceptor numbers of the probes to quantify the acidic and the basic parameters of the liquid crystal surface. The values obtained for and parameters indicated an acidic character for the surface of EBBA.

Use of inverse gas chromatography for the physicochemical characterisation of a new synthesised liquid crystal: (S)‐5‐(2‐methylbutoxy)‐2‐{[(4‐dodecyloxyphenyl)imino]methyl}phenol

A new liquid crystalline compound, i.e. (S)‐5‐(2‐methylbutoxy)‐2‐{[(4‐dodecyloxyphenyl)imino]methyl}phenol (MBDOPIMP), was prepared and characterised. Phase transition temperatures of MBDOPIMP were determined by polarising optical microscopy and differential scanning calorimetry. Trace amounts of ethyl acetate, butyl acetate, isobutyl acetate, hexane, heptane, octane, nonane and decane were passed through a chromatographic column loaded with MBDOPIMP coated on Chromosorb W. The retention diagrams of the solvents on MBDOPIMP were plotted using specific retention volumes at temperatures between 105 and 125°C. Thermodynamic parameters, such as Flory–Huggins liquid–solvent interaction, , equation‐of‐state liquid–solvent interaction, , effective exchange energy, X eff, the exchange enthalpy, X 12 and exchange entropy, Q 12, were determined for the liquid crystal–solvent systems. Subsequently, the partial molar heats of sorption, ΔH¯1,sorp and mixing, , were determined from the slopes of the plots of the logarithm of the specific retention volume, ln , versus 1/T and logarithm of the weight fraction activity coefficients, ln , versus 1/T, respectively.

Determination of exchange enthalpy and entropy parameters of the equation-of-state theory for poly(dimethyl siloxane) and some aromatic solvents by inverse gas chromatography

The specific retention volumes, V g o of toluene, ethyl benzene, n-propyl benzene and isopropyl benzene on poly(dimethyl siloxane)(PDMS) were measured at temperatures between 333 and 403K by inverse gas chromatography. The parameters of hard-core interaction, X t ∞, effective exchange energy, X 12 , exchange enthalpy, X 12 , and exchange entropy, Q 12 in the equation-of-state theory were determined. The parameters X t ∞ of the isopropyl benzene-PDMS pair decreased from 0.65 to 0.60 while those of others decreased from around 0.77 to 0.69 with increasing temperature. The values of the parameters X 12 also decreased as molecular weight of the substituted aliphatic group on the benzene ring of the solvent increased, ie 15J cm -3 in toluene and 5J cm -3 in isopropyl benzene. Both X 12 and Q 12 show negligible dependence on temperature.

Investigation of acid–base and surface characteristics of a thermotropic semifluorinated salicylaldimine liquid crystal by inverse gas chromatography

The surface energy of a semifluorinated salicylaldimine liquid crystal has been characterised by inverse gas chromatography over the temperature range 303 to 323 K using n-alkanes, tetrahydrofurane, dichloromethane, chloroform, acetone and ethyl acetate molecular probes. The dispersive component of the surface free energy of the adsorbent surface studied was calculated according to the approaches of Fowkes and Dorris–Gray in the infinite dilution region. The specific free energy, enthalpy and entropy of adsorption of polar probes on the liquid crystal were determined. The values of the specific enthalpy of adsorption were correlated with both the donor and the acceptor numbers of the probes to quantify the acidic and the basic parameters of the liquid crystal surface. The surface of the semifluorinated salicylaldimine liquid crystal was found to show a basic nature, which determined the nature of its interaction with the polar probes.

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

Abstract 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.

A new liquid crystal of considerable value for the separation of closely related solvents by gas chromatography

The synthesis, characterisation and mesomorphic properties of a new chiral liquid crystal, (S)-5-(10-undecenyloxy)-2-[[[4-(2-methylbutoxy)phenyl]imino]methyl]phenol (UMBPIMP) are described. The phase transition temperatures of this mesogenic compound have been investigated by optical polarising microscopy, differential scanning calorimetry and inverse gas chromatography. The thermodynamics of UMBPIMP were investigated in order to understand its selectivity as a stationary phase in gas chromatography. Its liquid crystal selectivity was tested using the isomers n-butyl acetate, tert-butyl acetate and iso-butyl acetate, and the isomers n-butyl alcohol, tert-butyl alcohol and iso-butyl alcohol, as model chromatographic probes. The retention diagrams of the isomers were plotted between 30°C and 110°C using inverse gas chromatography. Using the specific retention volume, , parameters such as the Flory–Huggins polymer–solvent interaction, , and hard-core polymer–solvent interaction, , and exchange parameters such as effective energy, X eff, enthalpy, X 12 and entropy, Q 12, were determined for the solvents chosen.

A study on the parameters of exchange enthalpy, X12, and entropy, Q12, in the equation-of-state theory for some polymer-solvent pairs

Abstract The parameters of exchange enthalpy, X 12 , and entropy, Q 12 have been determined for cyclopentane, tetrahydrofurane and 1,4-dioxane with poly(dimethyl siloxane) around room temperature using inverse gas chromatography technique. The parameters X 12 were compared to the parameters calculated by means of the Berthelot relationship from characteristic pressures of the pure components in the mixtures. The parameters Q 12 were compared to differences of thermal pressure coefficients of the pure components in the mixtures.