Dynamic Mechanical Analysis Flashcards
What is DMA used to study?
- The viscoelastic behavior of polymers
- Used to find the glass transition temperature range
How does a DMA determine the modulus?
A sinusoidal stress is applied and the strain in the material is measured
What leads to variations in the modulus in a DMA?
Temperature of the sample or the frequency of the stress being varied
What components make up a DMA tester?
Grips and an environmental chamber
What does a DMA measure?
- Stiffness (modulus)
- Storage modulus (E’)
- Loss modulus (E”)
- Damping (Tan delta)
What is the storage modulus (E’)?
- In phase component
- Measure of elastic response of a material (solid)
What is the loss modulus (E’’)?
- Out of phase component
- Measure of viscous response of a material (liquid)
- Measures the energy dissipated as heat
What is damping (Tan delta)?
Ratio of loss to the storage
What does damping measure?
- Energy dissipation of a material
- How good a material will be at absorbing a material
What range should delta be at, and what does it mean at each end point?
0 degrees
- as delta approaches 0 it also approaches a purely elastic behavior
90 degrees
- as delta approaches 90 the material approaches a purely viscous behavior
What does an increasing tan delta indicate?
- Material has more energy dissipation potential
- Greater tan delta means more dissipative your material is
What does a decreasing tan delta mean?
- That you material acts more elastic now
- By applying a load it has more potential to store the load rather than dissipating it
How do you get good data with a DMA?
- Specimen with good aspect ratio
- Correct geometry
- Deformation ~ 50 um
- Heating rate typically at 2~3 degrees C
What is the deflection temperature under load?
The temperature at which a polymer deforms under at a set load
What is DTUL used for?
To project long term, high temperature performance
Where is the DTUL in relation to the Tg for an amorphous PES?
Close to the Tg
What is DMA sensitive to?
Temperature
What transitions are clear with DMA that aren’t with DSC or DTA?
Secondary transitions
What sort of transition in polymers will generate a peak for tan Delta, E”, G”?
Any thermal transition
Do the peak maxima for G”, E” and tan Delta occur at the same temperature?
No
What does scanning across frequencies allow detection for?
Tg range
What is Tg shown as for storage modulus (E’) curve on a graph?
Drop
What is Tg shown as for tan delta curve on a graph?
The peak
What does a DMA detect in a polymer?
Relaxation and thermal changes
