Apparent heat capacity

Ferrari, M. E., and Lohman, T. M. (1994). Apparent heat capacity change accompanying a nonspecific protein-DNA interaction. Eschericia coli SSB tetramer binding to oligodeox-yadenylates. Biochemistry 33, 12896—12910. 

Low-temperature calorimetry (S83,B112) has been used to study coarse porosity. The method is based on the fact that water in pores freezes at a lower temperature than water in bulk. The ice forms through the advance of a front, analogous to the intrusion of mercury or the desorption of water. Hysteresis effects indicated the existence of necks in the pores, and the occurrence of up to three distinct peaks on curves of apparent heat capacity against temperature was interpreted as indicating maxima in the pore size distribution. Coarsening of the pore structure on drying was confirmed. 

Concentration in fluid phase in emulsion Concentration at L Concentration in inlet gas Concentration in outlet gas Apparent heat capacity of emulsion... 

FIGURE 4.9 Apparent heat capacity and optical microscopy measurement (% light transmission) of a 75/25 poly(oxyethylene)/poly(ether sulfone) blend. (From Dreezen, G., Groen-inckx, G., Swier, S., and Van Mele, B., Polymer, 42, 1449, 2001. With permission.)... 

Sturm (115) has described a systematic error in quantitative DTA that is caused by the change in the apparent heat transfer coefficient and the apparent heat capacity of the sample and sample holder. The logarithm of the peak area furnished an approximate measure of these changes the ratio of the logarithms of the areas of the standard and sample provided a correction factor for K. 

The fraction melted, F , at temperature, T , is equal to area ADE area ABC. The maximum value of the apparent heat capacity of the sample is zs. 

This equation gives the variation of the apparent heat capacity of the sample during melting, as a function of T. The upper limit of the melting process is T =7 (when F = l). The lower limit of the melting process is T < T0, when... 

In general, differences in heat energy uptake between the sample and reference cells required to maintain equal temperature correspond to differences in apparent heat capacity, and it is these differences in heat capacity that give direct information about the energetics of thermally induced processes in the sample. 

From Equations (2) and (3) it is obvious that the reversing heat capacity. Equation (4), makes use only ofthe middle term on the right-hand side of Equation (7). Thefirstterm is constant with time and contributes only to the last is a second harmonic and contributes only to a2 and b2 of Equation (2). The phase shift y is linked to the relaxation time X at v/a tan y = o)x, and the apparent heat capacity, which is measured as the reversing Cp, is equal to ... 

Finally, the left curves of Fig. 2.45 show that above about 260 K, melting of small, metastable crystals causes abnormal, nonlinear deviations in the heat capacity versus crystallinity plots. The measured data are indicated by the heavy lines in the figure. The thin lines indicate the continued additivity. The points for the amorphous polyethylene at the left ordinate represent the extrapolation of the measured heat capacities from the melt. All heat capacity contributions above the thin lines must thus be assigned to latent heats. Details of these apparent heat capacities yield information on the defect structure of semicrystalline polymers as is discussed in Chaps. 4-7. 

A more detailed analysis of the kinetics of the glass transition was carried out by quasi-isothermal TMDSC [66,67]. Figure 6.132 is a representation of plots of the reversing, apparent heat capacities of some of these samples after extrapolation to zero modulation amplitude. All traces of hysteresis are absent. The same methods as described in Sects. 6.3.1 and 6.3.2 were used for the analyses of the glass transitions. For the amorphous PET, the analysis is shown in Figs. 4.129-133 and 6.119-121. 

The value of apparent heat capacity, C, (not calibrated) may be written as follows [31]. 

Cp i f and Cp ef are the initial and final values of the apparent heat capacity in the glass transition region. It is assumed that the integration constant is independent of temperature. The above equation to calculate ACp only needs a one-point calibration for heat capacity selected in the transition region. The reason for this is that if it is assumed that the calibration constant of heat capacity is at the onset point of the glass transition and is K2 at the final point, ACp is given as follows. 

Figure 4.12. Line width of proton NMR signal and apparent heat capacity from DSC of...

There are six different thermodynamic contributions to the apparent heat capacity in the melting and crystallisation region of the analysed polymer [24]. The first three can be truly reversible, and the second three are increasingly irreversible. 

Figure 4.23. Evaluation of the heat of fusion for a sample melting over a broad temperature interval. A summary is given of the method of estimating a proper baseline and of the computation of crystallinity based on the measured apparent heat capacity and the baseline of...

Figure 4.47. Apparent heat capacity measured by DSC and MTDSC for POE5000 crystallised...

Figure 4.49 shows the results of adiabatic calorimetry, standard DSC and quasi-isothermal MTDSC for poly-/ -dioxanone (—CH2—CH2— O—CH2—COO—)x, (PPDX). The ordinate is labelled as apparent heat capacity since in the transition region, latent heat contributions may increase the heat capacity. Up to 250 K, the heat capacity is practically fiilly vibrational as is typical for glassy and crystalline solids. The skeletal and group vibrational contributions are then extrapolated to higher temperature, as is discussed with Figure 4.1 for polyethylene. The sample analysed with... 

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