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Difference Between Shear & Extensional Viscosity

2019-03-13 10:00 AM

As you know by now, viscosity is NOT just one number.

Viscosity is a defined property based on the type of continuous deformation applied. Although a steady shear flow is the most common characterization, extensional flow fields can also be used to analyze extensional viscosity. 

Shear rates are the foundation of performing viscosity experiments. Viscometers determine viscosity by dividing shear stress experienced by the fluid by the shear rate. When developing novel fluids, their viscosity must be measured to characterize the fluid behavior for multiple environments.

Shear viscosity, also known as apparent viscosity, is the shear stress applied to a fluid divided by the shear rate, or the relationship viscosity versus shear rate. For Newtonian fluids this relationship is constant and is known as Newton's Law of Viscosity. Most fluids however are non-Newtonian, meaning their viscosity is directly dependent on their shear rate (Shear Thinning or Thickening) or the deformation history (Thixotropic fluids).


Extensional viscosity is the resistance of a fluid to extensional flow. Any flow field involving a change in cross-sectional area will be affected by this material property. Therefore, extensional viscosity is a fundamental parameter in many industrial processes. Extensional deformation and extensional shearing have a significant impact on certain industrial processes, such as fiber spinning, paint rolling, roll coating, inkjet printing, spraying, electrospinning, enhanced oil recovery, drag reduction, and food processing.

Download our webinar to learn more about:

  • Clarify the difference between the steady shear and extensional viscosity
  • Discuss how the RheoSense product line is capable of measuring both types
  • Emphasize important points to consider when interpreting data

In this webinar, we will be introducing the e-VROC Chip: Shear Viscosity's Distant Cousin. 

e-VROC ChipThe e-VROC™ chip is engineered with a microfluidic channel of uniform width and depth. It has hyperbolic contraction/expansion zone in the middle of the channel and four monolithically integrated MEMS pressure sensors (two in the upstream and two in the downstream of the contraction/expansion zone). 

Register for our upcoming webinar "Extensional Viscosity with e-VROC: Theory & Practice" to learn more about extensional viscosity and the e-VROC viscometer. In this webinar we will review the theory behind our flow channel designed to measure extensional viscosity. We will also discuss practical aspects of testing with the e-VROC® including flow channel selection and the potential onset of secondary flows or turbulence.




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Before attending the webinar, we recommend checking out the application note on extensional viscosity. Access it for free by clicking the button to the right!   

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