Dynamic Mechanical Analysis (DMA)
| Instrument | Discovery 850, TA Instruments |
| Force range | 0.1 mN – 18 N ± 0.01 mN |
| Modulus | 1e3 – 3e12 Pa ± 1% |
| Deformation range | 0.005 µm – 10 mm |
| Temperature range | -160 – 600 °C |
| Temperature rate | 0.1 – 20 °C/min (heating) 0.1 – 10 °C/min (cooling) |
| Humidity range | 5 – 95% relative humidity |
Viscoelastic stresses and deformation
Measures the thermomechanical properties of a viscoelastic materials. A form of rheology, DMA, provides the storage (E’) and loss (E”) modulus. See below for some terms related to rheological measurements:
- Elastic (Young’s) modulus (E) – material stiffness, resistance to deformation; modulus = Stress / Strain
- Storage modulus (E’) – material’s ability to store deformation energy elastically
- Loss modulus (E”) – deformation energy losses from internal friction when flowing
- Loss tangent (tanδ) – damping or index of viscoelasticity
- Stress (σ) – measure of force as applied to an area (Force / Area)
- Strain (γ) – deformation of the material (change in material dimensions / original dimensions)
Mainly used on thin films, the storage and loss moduli can be measured as the temperature is ramped, resulting in the measurement of both thermal and mechanical effects on the material’s physical properties. DMA applies an oscillatory force to the sample which can be strain or stress controlled, normally at a constant frequency of 1 Hz. The DMA utilizes liquid nitrogen to reach cryogenic temperatures allowing for the analysis of nearly all polymers below their glass transition temperatures (Tg) before being able to ramp to a more elevated temperature**.
Rheology is a complex subject as is its measurements. Prior to running samples, understanding some of the principals of the methodology is highly recommended:
**Thermogravimetric analysis (TGA) may be beneficial prior to DMA measurements to get information about the material’s thermal stability. DMA experiments should only be performed at temperatures below the sample’s 5% decomposition temperature.