Isochoric and isobaric glass formation: Similarities and differences

Dina M. Colucci, Gregory B. Mckenna, James J. Filliben, Andre Lee, David B. Curliss, Keith B. Bowman, John D. Russell

Research output: Contribution to journalArticlepeer-review

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Pressure-volume-temperature (PVT) studies were performed on a glass-forming polymer, poly (carbonate) (PC), under both isobaric and isochoric (constant volume) conditions. An isochoric glass transition was observed and the formation points were found to be consistent with those obtained isobarically. Although the isobaric and isochoric responses were, as expected, the same in the rubbery state, the glassy state values were found to be different and dependent upon the glass formation history. The isobaric data exhibited larger changes in going from the rubber to the glass, hence a "stronger" glass transition, than did the isochoric data. Inserting the experimental values for the thermal expansion coefficient a and isothermal compressibility β, into appropriate thermodynamic relations, measures of the strength of each transition are defined. Strength estimates based on literature values of α and β are compared to the experimental measures of the isochoric and isobaric transitions. In addition, both the isobaric and isochoric PVT results were analyzed in terms of the Fox and Flory free volume theory which assumes that the glass transition is an iso-free volume state. While the isobaric results were consistent with the Fox and Flory theory, the isochoric results were not consistent with the idea of an iso-free volume glass transition.

Original languageEnglish
Pages (from-to)1561-1573
Number of pages13
JournalJournal of Polymer Science, Part B: Polymer Physics
Issue number10
StatePublished - 1997


  • Free volume theory
  • Glass transition
  • Isobaric
  • Isochoric
  • PVT behavior
  • Poly(carbonate)
  • Polymer


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