Reversing heat flow component

Cp X heating rate) is termed the reversing heat flow component. The non-reversing part is obtained by subtracting this value from the total heat flow curve. It is important to note that all... 

FIGURE 31-14 Deconvoluted thermogram from an MDSC apparatus showing nonreversing and reversing heat flow components. (Courtesy of TA instruments. New Castle. DE.)... 

Temperature modulated DSC Variation of DSC (or quantitative DTA) where a sinusoidal perturbation is applied to the temperature programme resulting in a non-linear modulation of the heat flow and temperature signals, which permits decomposition of the total heat flow signal into its reversing and non-reversing heat flow components. 

MDSC can be useful in resolving polymer glass transitions, which are otherwise difficult to analyze owing to concomitant solvent (or other volatile component) evaporation. The polymer glass transition is resolved in the reversing heat flow signal, while the contribution from the volatile component is observed in the non-reversing heat flow. 

An MTDSC experiment can not only generate the total heat flow similar to the heat flow obtained in conventional DSC but also separate the total heat flow into its reversing and nonreversing components. The total heat flow is the sum of the thermal events and is generally equivalent to the heat flow seen in conventional DSC. The reversing heat flow is the heat capacity component (plus other terms in some cases see text below) of the total heat flow Cp dT/dt as noted in Eq. (2.91)]. 

Figure 2.119. Separation of a scan of PET into the nonreversing component or IsoK baseline and the reversing or Thermodynamic heat capacity from an SSDSC experiment from the raw data labeled above. Upper curve shows the reversing heat capacity component bottom curve, is the IsoK baseline. An insert of the cold crystallization process demonstrates the temperature steps with the resultant modulated effect on the heat flow with its associated IsoK baseline. [From Ye (2006) courtesy of Perkin-Elmer.l...

Fig. 9 Modulated temperature DSC scans for (a) 74/26% PEEK/HAp with Tg 142°C, Tc 160°C and 347°C and (b) 37/63% PEEK/HAp with Tg 141°C, Tc 160°C, Tm 347°C. In both plots the total heat flow signal (solid line) has been split into (i) the non-reversing (kinetic) and (ii) reversing (heat capacity) components. Reprinted from [110] with permission from Springer...

Cp is the sample heat capacity. The first term on the right hand side of liquation 10.8 represents the heat flow of reversing thermal events and the second term represents the heat flow of nonreversing thermal events. XT , t) is also referred as to the kinetic component of heat flow. 

Hence, in the simplest terms, tmDSC is a description of the heat flow into the sample resulting from the sinusoidal modulation of the temperature program. Two properties of the sample can be investigated by tmDSC, the heat capacity which is directly related to the reversing component and a kinetically hindered thermal event which is related to the nonreversing component. Conventional DSC provides only a measure of the total heat flux into a sample as a function of temperature whereas tmDSC allows the heat capacity and kinetic components to be separated. However,... 

A variation of DSC is the MDSC (modulated DSC), wherein heat is applied sinusoidally, such that any thermal events are resolved into reversing and nonreversing components to allow complex and even overlapping processes to be deconvoluted. The heat flow signal in conventional DSC is a combination of... 

---