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Webinar: Back to Basics 

Why are some fluids non-Newtonian?
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Back to Basics: Viscosity Fundamentals

Whether you are a expert Rheologist or just getting into fluid characterization, you may be familiar with the terms Newtonian vs. non-Newtonian behavior. 

Never heard of it? No problem! Newtonian fluids are essentially fluids that have a linear relation between shear stress (mPa-s) and shear rate (1/s). This means that when shear rates vary, the viscosity remains consistent and the same value. A good example would be water.

Non-Newtonian fluids are fluids where their viscosity is dependent on shear rates. Here, we can go into further details where samples can be even more complex such as shear thinning or thickening (read more here). Essentially viscosity changes as shear rates change. A good example would be mayonnaise.

So whether you have ever noticed Newtonian behavior or non-Newtonian behavior, this is quite interesting insight into your sample characteristics. 

Download our webinar where we discuss the origins of non-Newtonian behavior and what viscosity data on these systems are telling you. 

1. What is Viscosity?

Viscosity of often referred to as the thickness of a fluid. You can think of water (low viscosity) and honey (high viscosity). However, this definition can be confusing when we are looking at fluids with different densities.

At a molecular level, viscosity is a result the interaction between the different molecules in a fluid.This can be also understood as friction between the molecules in the fluid. Just like in the case of friction between moving solids, viscosity will determine the energy required to make a fluid flow.  



2. How many shear rates do you recommend to analyze whether or not your sample is Newtonian or non-Newtonian?

We recommend a minimum of three different shear rates when analyzing your samples to determine whether they are Newtonian or non-Newtonian. Separately, the shear rates should have a wide range. The reason for the wide range is because many are complex. Sometimes, your sample will not show shear thinning or shear thickening behavior at low shear rates but will at high shear rates. 

Overall, there is just a lot to your sample that you may not know about until you actually test it. As a result, we recommend testing as much of a range as possible to ensure full knowledge of how your sample behaves. 

When it comes to your injections, the best way to design your experiments is by focusing on the injection rate that your sample will be exposed to when going from the syringe into a patient. Testing with those numbers in mind will help give you confidence and know what is the unknown.


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