Composition‐dependentglass transition temperature in mixtures: Evaluation of configurational entropy models*

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 massweighted 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.

Competing Effects of Cohesive Energy and Cross-Link Density on the Segmental Dynamics and Mechanical Properties of Cross-Linked Polymers

“…It is just this competing effect between cross-link density and cohesive interaction “strength” on fragility that complicates the prediction of the segmental relaxation of thermoset materials and, thus, their material design . In addition, the fragility is also found to be modified by the compositions without changing the cohesive energy or cross-link density of polymers, where the addition of oligomers, , plasticizers, and anti-plasticizers ,, would decrease the fragility compared to the pure polymer melts. For example, the work of Dalle-Ferrier et al found that the addition of an oligomer could modify the fragility of polystyrene/oligomer blends.…”

Editorial: In honor of Gregory B. McKenna's contributions to the field of polymer science

“…While there is evidence of a clear answer for the first question and there is significant progress concerning the second, for the last topic, many unanswered questions remain. In another article by Lopez et al, [ 2 ] mixing rules for the glass transition temperatures are scrutinized. As well as having an immediate relevance for the estimation of T g of blends, this study allows an insight on the origin of T g from the theoretical concept of configurational entropy.…”

Glass Transition Temperatures of Organic Mixtures from Isoprene Epoxydiol-Derived Secondary Organic Aerosol

“…Studies have used the Kwei equation to fit and explain the T g -composition relation of hydrogen bonding polymer mixtures. 55 − 57 In addition, the Kwei equation can also provide a good fit to the measured T g of binary mixtures of molecular liquids. 57 − 59 For example, the quadratic term of the Kwei equation used to fit the T g of binary blends of trehalose and choline dihydrogen phosphate was attributed to hydrogen bonding.…”

“… 55 − 57 In addition, the Kwei equation can also provide a good fit to the measured T g of binary mixtures of molecular liquids. 57 − 59 For example, the quadratic term of the Kwei equation used to fit the T g of binary blends of trehalose and choline dihydrogen phosphate was attributed to hydrogen bonding. 58 The Kwei equation has the potential to predict the T g of SOA mixtures when the Gordon–Taylor equation fails, particularly in the cases of substantial intermolecular interactions.…”

“…Kwei attributed the quadratic term q normalK normalw normale normali x normala ( 1 − x a ) to the effect of hydrogen bonding forming cross linkages in the polymer mixtures. Studies have used the Kwei equation to fit and explain the T g -composition relation of hydrogen bonding polymer mixtures. − In addition, the Kwei equation can also provide a good fit to the measured T g of binary mixtures of molecular liquids. − For example, the quadratic term of the Kwei equation used to fit the T g of binary blends of trehalose and choline dihydrogen phosphate was attributed to hydrogen bonding . The Kwei equation has the potential to predict the T g of SOA mixtures when the Gordon–Taylor equation fails, particularly in the cases of substantial intermolecular interactions.…”