Anomalous melting behavior of cyclohexane and cyclooctane in poly(dimethyl siloxane) precursors and model networks

Jinrong Wu, Gregory B. McKenna

Research output: Contribution to journalArticlepeer-review

7 Scopus citations

Abstract

Building on previous observations of anomalous melting behavior of solvents in polyisoprene, we have expanded our insight into the melting behavior of organic solvents in polymers and polymer networks through a calorimetric investigation of cylcohexane and cyclooctane in poly(dimethyl siloxane) (PDMS) precursors and model networks. The results are contrary to general expectations. Besides deviations between the predictions of the Flory-Huggins model and observed melting point depression of the small molecule organics, it is found that the melting point depression of cyclohexane in model networks is lower than that in the uncrosslinked precursors and unaffected by the molecular weight between crosslinks, which is not consistent with the general observation that higher crosslinking density leads to greater melting point depression. We interpret the observed phenomenon in terms of phase separation. In the case of cyclooctane, it exhibits a double melting peak in the model networks with high molecular weight between crosslinks. Furthermore, the heats of fusion of both cyclohexane and cyclooctane decrease with increasing polymer volume fraction which violates the underlying assumption that the heat of fusion of solvent in the polymer is the same as that in the bulk for both the Flory-Huggins model and the Gibbs-Thomson equation.

Original languageEnglish
Pages (from-to)2779-2791
Number of pages13
JournalJournal of Polymer Science, Part B: Polymer Physics
Volume46
Issue number24
DOIs
StatePublished - Dec 15 2008

Keywords

  • Confinement effects
  • Flory-Huggins theory
  • Gibbs-Thomson equation
  • Melting point
  • Melting point depression
  • Phase behavior
  • Polymer network
  • Polysiloxanes

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