Elements of Thermodynamics in DSC

Today DSC is a routine technique a DSC instrument can be found virtually in every chemical characterization laboratory, since the instruments are relatively inexpensive. Unfortunately, this has its drawback. It is a popular misconception that if you recorded a DSC peak, you did your job. In this chapter we would like to prove, from one side, that this is not true, but from the other side that despite this, DSC is still a simple and easily applied technique. Our goal is to present a simple but consistent picture of the present state of this measuring technique. 

Thermodynamics studies two forms of energy transfer heat and work. Heat can be defined as transfer of energy caused by the difference in temperatures of two systems. Heat is transferred spontaneously from hot to cold systems. It is an extensive thermodynamic quantity, meaning that its value is proportional to the mass of the system. The SI (Systeme International de Unites) unit of the heat is the joule (J). The earlier unit of calorie is not in use any more. 

The goal of thermodynamics is to establish basic functions of state, the most important of which (for differential scanning calorimetry) are U, internal energy H, enthalpy p, pressure V, volume S, entropy and Cp, heat capacity at constant pressure. 

As mentioned above, equilibrium thermodynamics deals with reversible processes, and is based on the following four laws of thermodynamics, which are empiric laws rather than theoretically deduced laws  

The first law of thermodynamics, also known as the principle of energy conservation, states that the change of internal energy of a thermody- 

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While a temperature-dependent IR spectrum allows one to examine specific elements of a transition, a DSC thermogram enables the visualization of transitions in their entirety and the calculation of associated thermodynamic parameters. The IR and DSC thermal profiles for identically treated samples of hydrated porcine SC are shown in Fig. 3. The results of a series of thermograms for intact, delipidized, fractionated, and reheated SC as well as extracted lipids suggest that these three major transitions near 60,70, and 95°C in intact SC are due to intercellular lipid, a lipid-protein complex associated with the comeocyte membrane, and intracellular keratin, respectively. Evidence supporting these deductions is elegantly presented by Golden et al. [33]. More recently, the presence of a subzero lipid transition at -9°C has also been reported [34]. 

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