Modulated DSC

Modulated DSC (MDSC ) is a patented technique from TA Instruments, New Castle, DE. In MDSC, a controlled, single-frequency sinusoidal temperature oscillation is overlaid on the linear temperature ramp. This produces a corresponding oscillatory heat flow (i.e., rate of heat transfer) proportional to physical properties of the sample. Deconvolution of the oscillatory temperature and heat flow lead to the separation of the overall heat flow into heat capacity and kinetic components. 

A disadvantage to the method is that calibration is required for temperature, enthalpy, and the heat capacity, as opposed to temperature and enthalpy only for standard DSC. 

Other advantages that have been claimed for the use of modulated DSC in the analysis of plastics and rubbers include the following  

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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. 

Androsch, R., Moon, I., Kreitmeier, S., and Wunderlich, B. (2000). Determination of heat capacity with a sawtooth-t rpe, power compensated temperature-modulated DSC. Thermochimica acta. 357-358,267-278. 

It is also possible to measure conductivity with DSC apparatus50 52. Khanna et al51 describe different procedures, whilst Simon and McKenna52 used temperature modulated DSC. A procedure using modulated DSC has been standardized in ASTM E195253. 

Differential scanning calorimetry (DSC) compares the two different heat flows one to or from the sample to be studied, and the other to or from a substance with no phase transitions in the range to be measured, e.g. glassmaking sand. Figures 1.45.1 and 1.45.2 show artist s views of parts of a modulated DSC system, and Figure 1.46 shows a commercial apparatus for DSC measurements. 

Fig. 1.45.1. Artist s view of a DSC cell in Tzero technology as used in modulated DSC (MDSC) processes. 1, Sample and reference table made from one piece of constantan 2, chromel thermocouples directly connected to the constantan tables 3, Tzero sensor from chromel-constantan in the middle between sample and reference table (TA Instruments, New Castle, DE, USA...

Fig. 1.46. Modulated DSC apparatus, Model Q 1000, using the details of Figs.l. 45.1 and 1.45.2 (TA Instruments, Newcastle, DE, USA)...

FIGURE 19.3 Measured specific heats of PA6 materials in the modulated DSC apparatus. 

The same techniques cannot be applied to the case of sPS/aPS blends, as the two components have similar Tg values (less than 10 °C difference). A higher resolution of close Tg values can be derived from the isothermal heat capacity curves, measured in the vicinity of Tg by modulated DSC [20]. Furthermore, sPS and aPS, when annealed separately below Tg, exhibit in both DSC and modulated DSC distinct endothermic transitions owing to the enthalpy recovery [20,21]. Both methods, when applied to the sPS/aPS blends, give a single temperature for all compositions in agreement with the presence of a miscibility between the components. 

This new technique introduced in 1993 has been thoroughly examined and discussed. Main advantages are the separation of overlapping events in the DSC scans. In conventional DSC, a constant linear heating or cooling rate is applied. In modulated DSC (MDSC), the normally linear heating ramp is overlaid... 

Royall PG. Craig DQM, Doherty C. Characterisation of the glass transition of an amorphous drug using modulated DSC. Pharm Res 1998 15 1117-21,... 

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.)...

Temperature modulated DSC (MDSC)2°2-204 jg another technique that has proved useful in the study of the glass transition " - where, it has been claimed, the approach is capable of providing better resolution and sensitivity than conventional DSC.2° In this, a modulated temperature programme is superimposed upon the conventional heating ramp and the resulting heat flows are interpreted in terms of two heat capacities an in-phase storage heat capacity and an out-of-phase kinetic heat capacity. Various theoretical procedures have been proposed for this and there is little doubt that the approach can provide information that is complementary to conventional DSC.2 ° However, the technique does involve slow temperature scans (cf. high-speed DSC above) and the authors feel that there are areas where the additional data are not, at present, easy to interpret. 

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... 

Lammert, A.M., Lammert, R.M., and Schmidt, S.J. Physical aging of maltose glasses as measured by standard and modulated DSC, /. Therm. Anal. Calorim., 55,949, 1999. 

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