Rheometer
| Instrument | Discovery HR-2, TA Instruments |
| Frequency range | 1e-7 – 100 Hz |
| Angular velocity range | 0 – 300 rad/s |
| Torque range | 2 – 200 nN.m (oscillation) 10 – 200 nN.m (steady shear) |
| Normal force | 50 N (maximum) |
| Strain step | 15 ms |
| Rate step | 5 ms |
Hydrogel stresses and deformation
Measures the flow and deformation of a material or the relationship between a material’s stress and deformation. Specially, it can provide information on the mechanical properties of a viscoelastic polymer or liquid sample. Experiments can determine the storage (G’) and loss (G”) modulus as well as viscosity, creep, and stress relaxation data. See below for some terms related to rheological measurements:
- Shear modulus (G) – material stiffness; modulus = Stress / Strain
- Storage modulus (G’) – material’s ability to store deformation energy elastically
- Loss modulus (G”) – 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)
- Viscosity (η) – deformation resistance as a function of shear rate or stress
- Creep – deformation under a constant force
- Stress relaxation – force necessary to maintain a constant strain
The rheometer is able to perform viscosity measurements that extend far beyond the limits of a traditional viscometer, characterizing non-Newtonian behaviors like shear thinning, thixotropy, and yield stress of complex fluids (emulsions, suspensions, paints, inks, coatings, slurries). Heating can also be used in order to generate time-temperature superposition plots that allow for the comparison of materials almost regardless of their flow behavior at a given shear rate.
Rheology is a complex subject as is its measurements. Prior to running samples, understanding some of the principals of the methodology is highly recommended: