Vibrational and configurational heat capacity of poly(vinyl acetate) from dynamic measurements

Tombari, E.; Ziparo, C.; Salvetti, G.; Johari, G. P.
July 2007
Journal of Chemical Physics;7/7/2007, Vol. 127 Issue 1, p014905
Academic Journal
The complex heat capacity Cp* of poly(vinyl acetate) has been measured at 20.95 mrad/s modulation frequency during the cooling as well as on heating at 24, 8, and 2 K/h and during cooling at 0.5 K/h. The study is complemented with (the rate-dependent) Cp,app measured during cooling and heating at 60, 24, and 8 K/h. At low temperatures, the real component of Cp* yields the unrelaxed Cp or Cp,vib, the vibrational part of Cp. It is found to be indistinguishable from Cp,glass and lies on a line extrapolated to its equilibrium melt’s temperature. At T near Tg,ΔCp(=Cp,melt-Cp,glass) shows no detectable contribution from Cp,vib. The finding conflicts with a modified entropy theory calculation [E. A. DiMarzio and F. Dowell, J. Appl. Phys. 50, 6061 (1979)], which had predicted that ∼27% of ΔCp of poly(vinyl acetate) at T near Tg is vibrational in origin and the remainder configurational. At T≤Tg, the real component of Cp* varies more slowly with T than Cp,app.


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