2022 article
Composition-dependent glass transition temperature in mixtures: Evaluation of configurational entropy models
Lopez, E., Koh, Y. P., Zapata-Hincapie, J. A., & Simon, S. L. (2022, May 20). POLYMER ENGINEERING AND SCIENCE, Vol. 5.
open access via onlinelibrary.wiley.com (publisher PDF)Abstract The composition dependence of the glass transition temperature ( T g ) in mixtures remains an important unsolved problem. Here, it is revisited using three model systems: a series of oligomeric and polymeric cyanurates, blends of oligomeric and polymeric α‐methyl styrene, and molecular mixtures of itraconazole and posaconazole. We evaluate several entropy‐based models to determine the theoretical T g as a function of molecular composition and compare the results against the experimental data. The assumption that the configurational entropy is invariant at the T g is tested, where the change in configurational entropy is assumed to be given by the integral of ΔC p dlnT, where ΔC p is the temperature‐dependent change in the heat capacity at T g . We find that, although the temperature‐dependent heat capacities in both liquid and glassy states are nearly independent of composition for several of the systems studied (i.e., they are nearly ideal mixtures), the composition dependence of T g is not well described by simply adding the changes in the mass‐weighted configurational entropy of the components on going from the T g in the pure state to that of the blend. The implication is that either configurational entropy is not invariant at T g or that it cannot be obtained from the integral of ΔC p dlnT.