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Nanoclay and polymer-based nanocomposites: Materials for energy efficiency 79

3.2.3.1 Differential scanning calorimetry (DSC)

Differential scanning calorimetry (DSC) is an instrument that measures the heat
capacity of small material samples called thermoanalytical technique. For PCMs,
the DSC gives the freezing and melting curves with the associated heats. In this tech-
nique, the sample and the reference are maintained roughly at constant rate temper-
ature during the measurement process. As a parallel recording, the excess heat
absorbed or emitted by the sample by integrating the temperature difference between
them that is proportional to the difference in heat flow between the two materials is
represented as the DSC curve. The latter is used to measure latent heat of fusion using
the area under the peak and melting/solidification temperature, generally determined
by the tangent at the point of highest slope on the face part of the peak [11]. The draw-
backs of this technique are the accentuated supercooling effects attributed to small
sample sizes and the poor nucleation effects [13].

3.2.3.2 Differential thermal analysis (DTA)
In this technique, the same principle of differential scanning calorimetry (DSC) is
applied, although it maintains the heat flux as constant and monitors the temperature
difference between the sample and the reference associated with material changes as a
function of time and temperature in a controlled atmosphere [7]. Thermal conductivity
is measured from DTA graphs that present the heat transfer rate at a variety of tem-
peratures. The mean disadvantage of such method can be quite the difficulty to cal-
ibrate to get quantitative heats of reaction and the incapability to measure multiple
samples simultaneously.

3.2.3.3 T-history method
This method is developed by Zhang et al. [14] to correct some problems in both
DSC and DTA techniques. It’s mostly used in the determination of the overall
PCM properties such as melting point, heat of fusion, and thermal conductivity to
measure the thermophysical properties of PCMs. Thus, the specimens are heated
and cooled in water baths for a specified period; the results are collected as temper-
ature versus time curves. This technique is simple and useful for a reliable character-
ization of PCM materials [14] and allows to observe the phase-change process of each
PCM sample (Fig. 3.2), giving a more realistic illustration of applied performance to
better found a desirable agreement between their test results and with those reported in
literature [16-18].

3.2.3.4 Thermal stability analysis of PCMs

The thermal gravimetric analyzer (TGA) is a much-used technique for characterizing
PCM thermal stability by analyzing the products of decomposition from the initial
samples. In this method, the material weight change is observed as a function of tem-
perature or time, while the thermograms were obtained in a controlled atmosphere