9: Thermomechanical, Dynamic Mechanical and Dielectric Methods

Thermomechanical analysis (TMA) is the study of the relationship between a sample's dimensions and its temperature whilst it is subject to a constant (or negligible) mechanical stress. Thus the thermal expansion of a specimen may be measured and softening temperatures determined. In a similar way, dynamic mechanical analysis (DMA) monitors the stiffness and mechanical damping properties of a material, both as a function of temperature but also as a function of rate of change of deformation. These properties are sensitive to molecular mobility and permit the study of physical processes such as melting, crystallisation or the glass transition as well as chemical processes such as the curing of thermosets. In an analogous fashion, the thermal response of a material exposed to a static or alternating electric field may be examined by measuring thermally stimulated currents or its dielectric properties respectively.