Dynamic Mechanical Analysis

Abstract

Dynamic mechanical analysis ( DMA ) is applying a stress or strain to a sample at controlled frequencies and analyzing the response to obtain phase angle and deformation data. These data allow the calculation of the damping or tan delta (δ) as well as complex modulus and viscosity data. Two approaches are used: (i) forced frequency, where the signal is applied at a set frequency, and (ii) free resonance, where the material is perturbed and allowed to exhibit free resonance decay. Most DMAs are of the former type, while the torsional braid analyzer ( TBA ) is of the latter type. In both approaches, the technique is very sensitive to the motions of the polymer chains, and it is a powerful tool for measuring transitions in polymers. More specialized techniques, such as the use of ultrasonics and laser pulses, do exist in specialized markets. It is estimated to be 100 times more sensitive to the glass transition than differential scanning calorimetry ( DSC ), and it resolves other more localized transitions, such as side chain movements that are not detected in the DSC. In addition, the technique allows the rapid scanning of a material's modulus and viscosity as a function of temperature, strain, or frequency. DMA may also be referred to as dynamic mechanical, thermal analysis ( DMTA ), dynamic mechanical spectroscopy ( DMS ), or dynamic thermomechanical analysis ( DTMA ).