If the sample contains solvent and parallel-plate, cone-plate or double-gap systems are used, the sample may dry out around the edge. The resulting measured viscosity is too high.
If possible, a cylinder measuring system should be used. Even if the sample surface dries out, this does not affect the results when using cylinder measuring systems.
When using cone-plate and parallel-plate measuring systems there are several ways of stopping the sample drying out:
- Coating the sample around the edge with low-viscosity silicon oil.
- Using a solvent trap which results in a saturated solvent atmosphere.
- If a Peltier-controlled hood is used, adding an Evaporation Blocker which optimally seals and reduces the sample area.
If the sample tends to sediment, the viscosity values may be too low as only the liquid phase is measured. For such samples using cylinder measuring systems is recommended.