Dynamic Mechanical Analysis (DMA) is a thermal analysis technique used to measure changes in the viscoelastic response of a material as a function of temperature, time, or deformation frequency. DMA is commonly used to determine quantitative flexural storage and loss moduli, shear storage and loss moduli, tan delta, and the dynamic and complex viscosity of materials. DMA is also particularly useful for qualitatively characterizing the glass transition temperature and other sub-Tg transitions of polymer and composite materials. A simplified explanation of the DMA technique may be described as follows. Typically, a sample is clamped into the DMA apparatus and subjected to an oscillatory deformation while being heated or cooled at some controlled rate. The resonant frequency of the sample and mechanical clamp assembly is continuously monitored as a function of temperature. As the viscoelastic response of the material changes over some temperature range, the electrical energy required to maintain a constant level of sample deformation also changes and is continuously monitored. Quantitative analysis routines are used to calculate the modulus (stiffness) and viscoelastic loss characteristics of a specimen as a function of temperature or time. Transition temperatures are readily obtained by determining the peak temperatures of the loss moduli or tan delta profiles.

Examples

• Block copolymer samples generally exhibit at least two distinct material phases. Since the mechanical loss characteristics of a material are directly related to molecular level motions, the DMA damping signal is particularly sensitive to a material's glass transition process. DMA loss profiles obtained on block copolymers generally show two distinct Tgs, which are related to the Tgs of the respective homopolymer components in the block copolymer, provided the inherent component material transitions are sufficiently well separated.
• Determining the glass transition temperature and the flexural storage and loss moduli of composite materials is a common DMA application. Composite samples exhibit dramatic changes in their damping (loss) profiles and display characteristic peaks as they pass through the glass transition temperature range. Modulus data for composite materials are obtained by subjecting test specimens to low strain displacements and then recording the corresponding sample response to such deformations.