Temperature TMDSC

Pyda and co-workers [49, 60] measured the reversible and irreversible PTT heat capacity, Cp, using adiabatic calorimetry, DSC and temperature-modulated DSC (TMDSC), and compared the experimental Cp values to those calculated from the Tarasov equation by using polymer chain skeletal vibration contributions (Figure 11.7). The measured and calculated heat capacities agreed with each other to within < 3 % standard deviation. The A Cp values for fully crystalline and amorphous PTT are 88.8 and 94J/Kmol, respectively. 

Kett et al. [1.162] studied Tg in freeze-dried formulations containing sucrose as a function of relative humidity and temperature during storage by TMDSC and ther-mogravimetric analysis. Craig et al. [1.163] found it helpful to asses the relaxation behavior of freeze-dried amorphous lactose by MTDSC. Relaxation times were calculated from measurements of Tg, and the magnitude of the relaxation endotherm. Scannnig was performed at 2°C/min with a modulation amplitude of 0.3 °C and a period of 60 s. 

TABLE 18.4. Select NOM Characterization Studies by Differential Scanning Calorimetry (DSC) and Temperature-Modulated Differential Scanning Calorimetry (TMDSC)... 

Dielectric relaxation, temperature-modulated differential scanning calorimetry (TMDSC), and H NMR spectroscopy (see Section 4.05.3.2.1) have been used to perform the dynamic characterization of fananserine 35. The use of these three different techniques gives a coherent set of information and allowed the authors to describe the dynamic properties over a wide range of frequencies and temperatures <2006MI798>. 

Temperature modulated DSC (TMDSC) is an advanced DSC technique in which the heating rate is modulated by superimposing a cyclic heating rate on the constant rate for example, a sinusoidal temperature modulation is superimposed on the temperature profile. 

Figure 10.6 Schematic temperature modulated DSC (TMDSC) curves for a polymeric sample. (Reproduced with permission from T. Hatakeyama and F.X. Quinn, Thermal Analysis Fundamentals and Applications to Polymer Science, 2nd ed., John Wiley Sons Ltd, Chichester. 1999 John Wiley Sons Ltd.)...

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,... 

It is generally acknowledged that DSC is the pre-eminent thermal analysis technique and that it has progressively become the established technique for the study of the thermal behavior of polymeric materials. Conventional DSC correlates thermal power with heat capacity and the integral thereof to energy and entropy. Thus, DSC has been applied to determine heat capacities of a wide range of materials. Conventional DSC is able to determine heat capacity to an uncertainty of 1-2% tmDSC is able to measure this parameter to an uncertainty of less than 1% with reproducible reliability. It is the temperature modulation feature of tmDSC which has confirmed this technique as the most versatile and most reliable of the thermal analysis techniques. Its versatility is further qualified by its ability to characterize the thermal behavior of materials without the need to have a detailed knowledge of the fundamental theoretical principles which underscore the basis of the technique. 

Thermal analysis techniques have had only limited use in the study of the various dental materials used for restorative, prosthetic and implant applications. The innovative research by Brantley s group, using conventional and temperature-modulated DSC (TMDSC) to examine the thermal behaviour of several metallic and polymeric dental materials, is described in Chapter 17 and numerous matters requiring additional research are identified. 

In 2001, Simon reviewed the theory of temperature-modulated DSC (TMDSC) with several examples of its applications, including many inorganic and coordination compounds [8]. Starink [9] provided a comprehensive review of the application of calorimetry in the analysis of a large variety of processes in aluminum-based alloys. 

A wide variety of dental materials is used in the oral environment for restorative, prosthetic and implant applications, and these materials are described at length in textbooks [1-3]. While their physical and mechanical properties have been studied extensively, there has been relatively little use of thermal analysis techniques to gain insight into dental materials. Our group has performed extensive research on several metallic and polymeric dental materials, principally utilizing conventional DSC and temperature-modulated DSC (TMDSC). These studies and thermal analysis studies of dental materials by other research groups are reviewed in this chapter. Although much novel information has been provided, numerous matters are discussed that require additional research. 

The placement of permanent bends of 135 in the nickel-titanium archwires failed to yield definitive increases (Afl" values) for the low-temperature martensite peaks on the TMDSC plots, compared to those for the as-received wires [35,37], It was assumed that bends with acute angles would be needed to increase the amount of work-hardened martensite sufficiently to cause significant increases in the enthalpy changes associated with these low-temperature peaks. 

Additional TMDSC study of other vinyl polysiloxane, polyether and polysulfide impression materials is important to verify if the polymer transitions shown in Figures 16 to 19 generally exist in different products and to investigate the effects of other temperature modulation conditions. Complementary research on correlations with clinically relevant mechanical properties of the elastomeric impression materials is needed to verify if these thermal analyses have useful predictive power. Interestingly, when compared at apparently similar viscosities, the reported values of the elastic modulus [3] are highest for the vinyl polysiloxane silicone impression materials, intermediate for the polyether impression materials, and lowest for the polysulfide impression materials, in reverse order to the relative values of Tg fovind in our thermal analyses [45]. Our X-ray diffraction and scanning electron microscopic study [47] of these impression materials has shown that they contain substantial amounts of crystalline filler particles in the micron size range, which are incorporated by manufacturers to achieve the clinically desired viscosity levels. Tliese filler particles should have considerable influence on the mechanical properties of the impression materials. 

---