Conventional methods fail to measure cp(omega) of glass-forming liquids

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The specific heat is frequency dependent in highly viscous liquids. By solving the full one-dimensional thermoviscoelastic problem analytically it is shown that, because of thermal expansion and the fact that mechanical stresses relax on the same time scale as the enthalpy relaxes, the plane thermal-wave method does not measure the isobaric frequency-dependent specific heat cp(omega). This method rather measures a "longitudinal" frequency-dependent specific heat, a quantity defined and detailed here that is in between cp(omega) and cV(omega). This result means that no reliable wide-frequency measurements of cp(omega) on liquids approaching the calorimetric glass transition exist. We briefly discuss consequences for experiment.
TidsskriftPhysical Review E (Statistical, Nonlinear, and Soft Matter Physics)
Udgave nummer4
Antal sider11
StatusUdgivet - 2007

Bibliografisk note

Paper id:: 041502

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