Glass transition temperature measurement method
Vitrification is the process of converting a substance into a glassy amorphous body (glassy state), which is a state between a liquid state and a solid state, in which no crystal structure exists. The measurement of the glass transition temperature Tg by a differential scanning calorimeter is based on the fact that the heat capacity increases when the polymer transitions at the glass transition temperature.
On the DSC curve, it appears that the baseline moves toward the endothermic direction as it passes through the glass transition temperature. As shown in Figure 1. Point A in the figure is the point at which starting from the baseline. Extending the baseline before and after the transition, the vertical distance ΔJ between the two lines is called the step difference, and the point C can be found at ΔJ/2. The tangent from point C intersects the front baseline extension line at point B. ICTA recommends using point B as the glass transition temperature Tg. The glass transition temperature, which does not have a very fixed value, varies depending on the method and conditions of the assay. Therefore, when the glass transition temperature of a polymer is marked, the method and conditions of the measurement should be noted.
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