Entropy−Enthalpy Compensations in Solutions of Dual Character Molecules with Polymeric Chromatographic Liquid Phases

Abstract

Careful gas chromatographic studies provide thermodynamic data for insights into solution processes in nonvolatile solvents. Using 24 solutes and five stationary phases, several entropy-enthalpy compensation effects in the thermodynamics of solution were identified. Despite solute structure differences, when excess enthalpy and entropy of solutions were examined, entropy-enthalpy compensation effects were found in solvents dominated by single types of interaction: squalane and, to some extent, methoxy poly(ethylene oxide) (PEO). The main reason for the absence of linearity in other solvents is pure solute state interactions in the reference state and the multicharacter nature of solvents. In this study, consideration of solute state interactions was removed through examination of the thermodynamics of transfer between solvent pairs. It was found that solute transfers from squalane to poly[methyl(trifluoropropyl)siloxane] (QF-1) and to poly(methylphenyl) (DC-550) also gave linear relationships. The former system contains a second correlation for ester type solutes. The transfer data for squalane to poly(methylsiloxane) (DC-200) had smaller ranges and were more scattered. The effects of derivatizing groups on the transfer enthalpy and entropy were treated as a summation of hydrocarbon cores with the derivative groups. The group properties of transfer then also show entropy-enthalpy compensation effects. Many solution effects could be explained on the basis of solvent composition and local interactions with solutes.

Multiparameter solubility model of fullerene C60

“…In this study, it is proposed to avoid the difficulty associated with the solid reference state by studying the difference of thermodynamic properties of the solute between two solvents; that is, the transfer thermodynamic functions between the two solvents. In a recent study Huang et al [16] proposed that the effects of liquid-state interaction of a liquid solute could be removed by comparing solution properties of the solute between two solvents. The solid-state interaction of a solute will also be cancelled in the calculation of transfer properties between two solvents.…”

“…In examining the solubility of a solute in solvents the combination of Hildebrand solubility parameter model [14,15] and Flory-Huggins theory [16] is commonly used. In this method the activity coefficient is considered to be the product of two components: the athermal or Flory-Huggins part, γ F-H , and thermal part, γ T :…”

Linear solvation energy relationship and evaluation of mutual miscibility of polymers using inverse gas chromatography data

“…This quantity is proportional to the transfer free energy for solutes to move from one polymer to another polymer. It was pointed out by Huang et al 14 that in calculating transfer properties of a solute between two solvents the solute liquid state interaction of all probes can be eliminated. Therefore, the large contribution of hydrogen bonding interaction in the solute liquid state in alcohols is removed when transfer properties are used.…”

Entropy–enthalpy compensation in solution properties of solutes at infinite dilution in nonpolar polymers

“…[3][4][5][6][7][8] From sorption data of low molecular weight solutes in polymers at several temperatures one can obtain the enthalpy and entropy of the solution process. In a recent study Huang et al 9 showed that linear entropy-enthalpy relationship was observed in IGC study of solutes in a nonpolar hydrocarbon solvent and a polar polyethylene oxide solvent. For some moderately polar solvents the correlation was less noticeable.…”

“…Furthermore, the variation in solution properties among solutes reflects the difference in interaction within pure solute liquids. 9 Thus, one might see a good correlation between heat of vaporization and enthalpy of solution for solutes in nonpolar solvents. This is explored in the present study.…”