Chapter 15: Viscoelastic and Rheological Properties

15.1.1 Theory

Dynamic mechanical analysis (DMA) provides putative information on the viscoelastic properties - modulus and damping - of materials. Viscoelasticity is the characteristic behaviour of most materials in which a combination of elastic properties (stress proportional to strain rate) are observed. A DMA simultaneously measures both elastic properties (modulus) and viscous properties (damping) of a material.

DMA measures changes in mechanical behaviour such as modulus and damping as a function of temperature, time, frequency, stress, or combinations of these parameters.

The technique also measures the modulus (stiffness) and damping (energy dissipation) properties of materials as they are deformed under periodic stress. Such measurements provide quantitative and qualitative information about the performance of the materials. The technique can be used to evaluate elastomers, viscous thermoset liquids, composite coatings, and adhesives, and materials that exhibit time, frequency, and temperature effects or mechanical properties because of their viscoelastic behaviour.

Some of the viscoelastic and rheological properties of polymers that can be measured by DMA are [1, 2]:

• Modulus and strength (elastic properties)

• Viscosity (stress strain rate)

• Damping characteristics

• Low- and high-temperature behaviour (stress strain)

• Viscoelastic behaviour

• Compliance

• Stress relaxation and stress relaxation modulus

• Creep

• Gelation

• Projection of material behaviour

• Polymer lifetime prediction

Basically this technique involves the measurement of the mechanical response of a polymer as it is deformed under periodic stress and is used to characterise the viscoelastic and rheological properties of polymers.

DMA is the measurement of the mechanical response of a material as it is deformed under...