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

Phys Rev E Stat Nonlin Soft Matter Phys

DNRF centre Glass and Time, IMFUFA, Department of Sciences, Roskilde University, Postbox 260, DK-4000 Roskilde, Denmark.

Published: April 2007

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 c{p}(omega) . This method rather measures a "longitudinal" frequency-dependent specific heat, a quantity defined and detailed here that is in between c{p}(omega) and c{V}(omega) . This result means that no reliable wide-frequency measurements of c{p}(omega) on liquids approaching the calorimetric glass transition exist. We briefly discuss consequences for experiment.

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http://dx.doi.org/10.1103/PhysRevE.75.041502DOI Listing

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