Dynamic mechanical analysis
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Dynamic mechanical analysis (DMA), dynamic mechanical thermal analysis (DMTA) or dynamic thermomechanical analysis is a technique used to study and characterize materials. It is most useful for observing the viscoelastic nature of polymers. An oscillating force is applied to a sample of material and the resulting displacement of the sample is measured. From this the stiffness of the sample can be determined, and the sample modulus can be calculated. By measuring the time lag in the displacement compared to the applied force it is possible to determine the damping properties of the material.
Viscoelastic materials such as polymers typically exist in two distinct states. They exhibit the properties of a glass (high modulus) at low temperatures and those of a rubber (low modulus) at higher temperatures. By scanning the temperature during a DMA experiment this change of state, the glass transition or alpha relaxation, can be observed. The glass transition temperature (Tg) is often measured by DSC (Differential Scanning Calorimetry), but the DMA technique can often yield better data and can also be used to investigate the frequency (and therefore time) dependent nature of the transition. DMA can also resolve beta transitions in many materials that the DSC technique is not sensitive enough to pick up.
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