Temperature Modulated DSC: Principles, Applications, and Measurement Examples

The conventional Differential Scanning Calorimetry (DSC) method measures heat flow and temperature variations, such as glass transition, crystallization, or melting, by detecting differences in heat flow between a sample and a reference material during heating or cooling at a constant rate. On the other hand, AC calorimetry measures the specific heat capacity of a sample by analyzing the oscillation in its temperature when periodically heated. This method has been widely used for specific heat capacity measurements.

Temperature Modulated DSC (TM-DSC) combines the periodic temperature control used in AC calorimetry with the constant rate temperature control of traditional DSC. This hybrid method allows simultaneous acquisition of specific heat capacity data (referred to as the Reversing Heat Flow) and conventional DSC data. While the Total Heat Flow represents the data from standard DSC measurements, subtracting the Heat Capacity Component from the Total Heat Flow yields the Kinetic Component (Non-Reversing Heat Flow).

This article introduces the principles of TM-DSC and explores its applications.

Temperature Modulated DSC

Principle In traditional DSC, heat flow differences (ΔQ\Delta Q) between the sample and reference material are measured during constant-rate heating. TM-DSC modifies this by introducing sinusoidal temperature modulation superimposed on linear heating, raising the sample temperature at an average constant rate through repeated short-term heating and cooling cycles (Figure 1).

By reversing the time variable, the equation separates the Heat Capacity and Kinetic Components. These components can be extracted through data analysis using Fourier Transform and contour integration, as illustrated in Figure 2.

Features

TM-DSC offers several advantages over conventional DSC, including:

• Improved resolution for overlapping or proximate transitions.
• Enhanced detection of small or secondary transitions.
• Simultaneous separation of Heat Capacity and Kinetic Components.
• Accurate measurement of specific heat capacity, especially at low heating rates.

This method is particularly beneficial for analyzing complex thermal behaviors, such as overlapping glass transitions, curing reactions, or phenomena influenced by thermal history.

Measurement Examples

Amorphous Polyethylene Terephthalate (PET) In amorphous PET, TM-DSC detects glass transition (75–82°C), cold crystallization (132°C), and melting (256°C) in the Total Heat Flow. The glass transition and melting appear in the Heat Capacity Component, while cold crystallization and melting are evident in the Kinetic Component.

Glass Transition with Enthalpy Relaxation For cured epoxy resin, enthalpy relaxation may overlap with the glass transition, appearing as a broad endothermic peak. TM-DSC effectively separates the glass transition (Heat Capacity Component) from the enthalpy relaxation (Kinetic Component), enabling accurate identification.

Curing Reaction of Thermoset Polymer For uncured epoxy resin, the glass transition (~70°C) and curing reaction (~180°C) overlap in the Total Heat Flow. TM-DSC isolates the curing reaction in the Kinetic Component, providing precise thermal behavior analysis.

Immiscible Polymer Blends In a PET-PC blend, overlapping cold crystallization (PET) and glass transition (PC) hinder conventional DSC analysis. TM-DSC separates these transitions, attributing the glass transition to the Heat Capacity Component and cold crystallization to the Kinetic Component.

Vaporization in Nylon Fibers Nylon, with its hydrophilic amide groups, absorbs moisture, leading to overlapping vaporization and glass transition signals. TM-DSC distinctly identifies the glass transition in the Heat Capacity Component while attributing vaporization to the Kinetic Component.

Crystal Polymorphism in Pharmaceuticals In pharmaceuticals, crystal polymorphism presents complex thermal behavior. TM-DSC identifies transitions like metastable crystal fusion and stable crystal melting by separating reversible and irreversible thermal phenomena, enabling detailed phase behavior analysis.

Conclusion

TM-DSC enhances traditional DSC by offering detailed separation of thermal transitions into Heat Capacity and Kinetic Components. This enables more precise analysis of complex materials, improving efficiency and accuracy in thermal characterization.