Differential Scanning Calorimetry

Literature Review and result analysis

Basic Principle: Differential scanning calorimetry is to study the change of the physical quantity of the substance with the temperature change under the temperature program control, that is to measure the relationship between the power difference input to the sample and the reference material and the temperature under the program temperature control. ^[1]

Figure 1 shows the schematic diagram of the differential scanning calorimeter, which includes a sample placement area and a standard placement area. The two were heated under the same program control to compare the relationship between the power difference and the temperature of the input sample and standard material.

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Figure 1: Diagram of a heat flux DSC ^[2]

Figure 2 shows the peaks of the curve that may appear when performing a differential scanning calorimetry analysis. The upward peak occurs when the sample undergoes an exothermic reaction, and the downward peak occurs when the sample undergoes an endothermic reaction. Figure 3 shows the microstructure changes of polymer materials when they undergo temperature changes. When analyzed by differential scanning calorimetry, the two most obvious peaks of the curve appear at the glass transition and melting, respectively.

Figure 2: Image for DSC analysis^[2]

Figure 3: Change curve of the modulus of polymer materials with temperature ^[2]

Figure 4: DSC curves of PBD (polybutadiene), EPBD (epoxidized polybutadiene), OTPB (oxime-terminated polybutadiene) and AmTPB (amine-terminated cis-polybutadiene).^[4]

The thermal properties such as glass transition temperature (Tg) and melting point (Tm) were analyzed by differential scanning calorimetry (DSC) (Figure 4). PBD, OTPB and AmTPB with higher cis-1,4 content have relatively lower Tg at −105℃ due to their polybutadiene chains. At −5°C and −10°C, there are obvious melting peaks due to their regular chain structure. For EPBD, however, the rigid epoxy bond reduces the flexibility of the polymer chain, destroys the regularity of the chain structure, and its Tg increases to −92°C. Also, the melting peak disappears. The DSC curves of OTPB and AmTPB show cold crystallization peaks at −40℃~−60℃. This may be caused by polar groups (oxime group and amino group) at the ends of the non-polar polymer chains which can block the movement of these polymer chains and impair the crystallization ability of polybutadiene^[4]. On the other hand, OTPB and AmTPB may undergo a slight crystal form transition during heating, resulting in a small exothermic peak at −25℃.

Figure 5: Temperature rise curve and heat flow curve with time

Differential scanning calorimetry analysis was performed on a 1.8 mg sample at a temperature range of 25°C to 160°C. The melting interval of the sample can be determined by the DSC method.

Figure 6: DSC peak and two possible baseline constructions (a and b).^[2]

This diagram shows the effect of impurity (curve c) which reduces the melting point and broadens the melting profile.^[2] It shows that impurities or additives can change the size, position and width of the endothermic or exothermic peaks of the sample.

Figure 7: Specific heat capacity of cis-PBD(Left)^[3] and experiment result (Right)

According to the comparison between the position and size of the absorption peak and the sample, it can be judged that the sample contains some additives that prevent melting, which makes the absorption peak smaller and wider.

Reference:

[1] Höhne, G., McNaughton, J. L., Hemminger, W., Flammersheim, H. J., & Flammersheim, H. J. (2003). Differential scanning calorimetry. Springer Science & Business Media.

[2] Gabbott, P. (2008). A practical introduction to differential scanning calorimetry. Principles and applications of thermal analysis, 1-50.

[3] Di Lorenzo, M. L. (2009). The melting process and the rigid amorphous fraction of cis-1, 4-polybutadiene. Polymer, 50(2), 578-584.

[4] Xu, L., Jie, S., Bu, Z., & Li, B. G. (2021). Preparation of primary amine-terminated polybutadiene from cis-polybutadiene. European Polymer Journal, 152, 110484.

Characterisation data

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