1. Introduction
2. Principle of DMA
It is most useful for studying the viscoelastic behavior of polymers. A sinusoidal stress is applied and the strain in the material is measured, allowing one to determine the complex modulus. The temperature of the sample or the frequency of the stress are often varied, leading to variations in the complex modulus; this approach can be used to locate the glass transition temperature of the material, as well as to identify transitions corresponding to other molecular motions.
The instrumentation of a DMA consists of a displacement sensor such as a linear variable differential transformer, which measures a change in voltage as a result of the instrument probe moving through a magnetic core, a temperature control system or furnace, a drive motor (a linear motor for probe loading which provides load for the applied force), a drive shaft support and guidance system to act as a guide for the force from the motor to the sample, and sample clamps in order to hold the sample being tested. Depending on what is being measured, samples will be prepared and handled differently.
3. Uses of DMA
Viscoelastic properties such as:
-Storage modulus: E’, G’ (purely elastic component)
-Loss modulus: E”, G” (purely viscous component)
-Loss tangent: tanδ (=E”/E’),
can be measured by DMA, and their dependence on temperature and frequency can be analyzed.
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