Why ASC?

Adiabatic scanning calorimetry (ASC) is a proven technique for the high-resolution determination of the enthalpy and heat capacity of materials. It keeps the sample in thermodynamic equilibrium and excels at measuring phase transitions, both very small and subtle ones as well as large melting transitions.

Key advantages for the measurements:

  • The sample remains in thermodynamic equilibrium.
  • The sample evolves freely through a phase transition.
  • High resolution in temperature: sub-millikelvin.
  • Absolute values always within 2 %.
  • True shape of heat capacity curves: no instrument influences.

Key advantages for operation:

  • Suitable for all types of liquid and solid samples.
  • No need for temperature calibration.
  • No need for caloric calibration.

Key advantages for data analysis:

  • Enthalpy available independent of heat capacity.
  • No baseline correction needed.

How does it differ from DSC?

An inverse concept

In a DSC, a fixed temperature rate is imposed on the sample. This means that the behaviour of the sample is enforced: the calorimeter controls the sample.

In an ASC, the sample is given a fixed amount of power, and is free to do with that energy what it wants to do. The ASC then follows the evolution of the sample. In other words, the sample controls the calorimeter!

The basic premise that the sample in an ASC is free, while it is forced in a DSC, also has a number of other consequences, most importantly these.

  • The sample remains in thermodynamic equilibrium.
  • Phase transitions are not deformed by the instrument.
  • High-resolution separation of small and close phase transitions is possible.

Enthalpy as a primary result

Another effect of the constant power operation is that the enthalpy is a primary ASC measurement result: it is obtained independently of the heat capacity. This contrasts the situation in DSC results, where the enthalpy is obtained as the integral of the heat capacity, and a lot of care needs to be given to these calculations.

The availability of the enthalpy independently from the heat capacity leads to new possibilities for data analysis and interpretation.

The absence of the baseline

An ASC also does not have a variable baseline. As an absolute technique, the calorimeter and addenda background is factory-provided and does not change with the experimental circumstances.

Multimode calorimeter

Apart from its primary mode of operation, the adiabatic scanning mode, an ASC can also run in several other modes of operation. These alternative modes correspond to other calorimetric techniques such as DSC.

Heat-flux constant rate mode
This mode of operation is equivalent to the working of a heat-flux DSC, the most common type of DSC. The calorimeter is heated up at constant rate, while the heat flux between the sample and the environment is measured.
Power-compensated constant rate mode
This mode of operation is equivalent to the working of a power-compensated DSC. The calorimeter is heated up at constant rate, while the power needed to keep the sample at the same rate is provided by an electrical heater at the sample holder.
Heat-step calorimeter mode
This mode of operation is equivalent to the working of a classical heat-step or adiabatic calorimeter. A large amount of heat is provided to the sample in a short time. From the consequent temperature increase, the heat capacity is calculated.

Fields of application

ASC can be used to study any type of liquid and solid. However, there are a number of applications where it excels.

Small and close transitions
The high temperature resolution and operation in thermodynamic equilibrium lead to a large separating power. It is for an ASC no challenge to detect several small transitions within a single degree.
Correct curve shapes.
Since the sample controls the instrument, the true behaviour of the sample is measured. Thus, the results reflect the sample, free of any instrument parameters.

The use of ASC has been proven in a number of fields.

  • Liquid crystals
  • Phase change materials (PCM)
  • Reference materials
  • Lipid solutions