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

Abstract

The knowledge of the Flory-Huggins interaction parameter, w, between organic liquids and polymers is very important in the study of their miscibility. From the temperature dependency of w the enthalpy and residual entropy of solution can be determined. In this study literature data of thirty-two solutes, ranging from alkanes to alcohols, at infinite dilution in isotatic polypropylene, poly(ethyl ethylene), and poly(dimethylsiloxane), were tested and linear entropy-enthalpy compensation was observed. The plot of residual free energy versus enthalpy of solution was also linear, with a lower correlation coefficient than the entropyenthalpy plot. The range of enthalpy of solution was wider than those of the size corrected free energy of solution. In nonpolar solvents the enthalpy of solution reflected largely the interaction within the solute liquid state, and showed a linear trend with respect to solute cohesive energy density for n-alcohols. The wide range of enthalpy of solution suggests the use of a two-dimensional solubility parameter model to correlate the enthalpy of solution.

Estimation of solubility parameter components of solutes and polymers using heat of vaporization and heat of sorption of solutes

“…Therefore, for polar solutes, an increase in Δ U vap is accompanied by a more positive Δ U s . This was demonstrated in a recent study by Huang 8. A proportional trend between cohesive energy density and specific enthalpy of solution was observed for solutes ranging from n ‐alkanes to alcohols when poly (ethyl ethylene) (PEE), polypropylene (PP), and poly(dimethylsiloxane) (PDMS) were used as the solvents.…”

“…The resulting parameters of PDMS are listed in Table II. In a previous study, PEE had a small polar component 8. In this study, λ 2 of PEE was assigned to be zero because a plot similar to Figure 3 did not yield a trend.…”

“…However, eq. (8) was shown to be able to correlate the heat of solution of a range of solutes in PP, PEE, and PDMS 8. But, the correlation had some scattering for solutes with low values of Δ U s / V of solution.…”

“…(8) was used in the free energy of solution with the Flory‐Huggins expression, a negative correction term proportional to the polar term was necessary 13–16. In the previous study, it was suggested that the correction might be related to the entropy‐enthalpy compensation effect, which reduced a portion of the polar component term in the free energy of solution 8. However, eq.…”

“…This was demonstrated in a recent study by Huang. 8 A proportional trend between cohesive energy density and specific enthalpy of solution was observed for solutes ranging from n-alkanes to alcohols when poly (ethyl ethylene) (PEE), polypropylene (PP), and poly(dimethylsiloxane) (PDMS) were used as the solvents. However, the data of nonpolar and slightly polar solutes were scattered.…”