<img height="1" width="1" style="display:none;" alt="" src="https://dc.ads.linkedin.com/collect/?pid=510762&amp;fmt=gif">

Importance of Viscosity: How to Measure it

Posted by Eden Reid on Jul 28, 2020 11:38:08 AM

In Viscosity Measurements, VROC Technology, shear rate, non-Newtonian, dynamic viscosity, kinematic viscosity, microfluidic, rectangular slit viscometer

In simplest terms, viscosity is defined as “the resistance to flow” and is often referred to as the thickness of a fluid. The concept of a fluid having a “thickness” has existed for thousands of years, however the term “viscosity” was not introduced until 1929. Even Newton referred to viscosity as “the lack of slipperiness of the parts of the liquid” (Sir Isaac Newton, Principia, 1687).

When you think of a viscometer, what primarily comes to mind is an instrument capable of measuring viscosity. However, we know viscosity can be calculated, but cannot be measured directly. Viscosity can be calculated using various methods and there are numerous viscometers on the market today, but not all viscometers are made alike.

 

Falling Ball 

Spindle Type

Rotational 

Rectangular Slit Method

Funnel Type 

Glass Capillary

Oscillating Piston

Stabinger

Bubble

Sample Size

mL (some require 40 mL!) 

mL (6.7 - 16 mL)

2 - 20mL

µl (26-100)

Large

mL

mL (1.5 mL - 6 mL)

mL (1.5 - 6 mL)

mL

Primary Measurement

Time (Terminal Viscosity)

Torque

Stress Control or Shear Control

Pressure Drop

Time

Time

Shear Stress

Shear Stress

Time

Viscosity Measured

Dynamic

Dynamic

Dynamic

Fluid Viscosity

Kinematic

Kinematic

Kinematic

Kinematic

Kinematic

Shear Rate Variation

Yes (Must change the angle)

Yes

Yes

Yes

No

No

Yes

No

No

Laws/ Principle applied

Stoke’s Law, Hoeppler Principle

Couette/Searle 

Couette/Searle 

Hagen-Poiseuille Flow

Time

Gravimetric Flow

Electromagnetic 

Couette

Time

Benefits

"Repeatable"

Wide variety of sample capability

ASTM standards

Accurate characterization of shear rates


Flexible to all types of geometry


Characterizes viscoelastic behavior (G',G'')
Thixotropy

 Small sample volumes

Accurate measurements

Easy to use

Low reynolds numbers

Quick quality control

Simple design

ASTM Standards

Measures kinematic and dynamic viscosity also density

Quick quality control

Limitations

Rely on Gravity-driven flow

Shear rates not controlled or changed


Difficult to use and clean


No Viscoelastic characterization

Hard to reproduce measurements

Evaporation

Irreversible adsorption of protein molecules at the interface


Calibration before every experiment is key

Careful attention to cleaning and fibers


No Viscoelastic characterization

Rely on Gravity-driven flow

Shear rates not controlled or changed


No Viscoelastic characterization

End user variation

easy to break and lose track of measurement

No Viscoelastic characterization

Variation from end users

No Viscoelastic characterization

No Viscoelastic characterization

No Viscoelastic characterization

End user dependent

When measuring viscosity, it is important to know if the fluid you are working with is Newtonian or non-Newtonian. Viscosity of Newtonian fluids is constant and therefore independent of shear rate whereas the viscosity of non-Newtonian fluids is not constant and therefore dependent on shear rate. (1) Many viscometers on the market today are only capable of accurately measuring viscosity of Newtonian fluids, when in reality most fluids are non-Newtonian. And, often only approximate the apparent properties of fluids, failing to quantify the absolute or true viscosity, which is one of the most important parameters in the development and modeling of applications that involve fluid flow. Behavior of Non-Newtonian fluids affects both production and how they are applied (ex: injectability, lubrication, spreading, jetting or drinking). Viscometers that don’t allow you to control shear stress or shear rate cannot adequately characterize Non-Newtonian liquids, and it is difficult to understand your sample’s behavior under production or application conditions without the ability to test under these same conditions.

Learn More About  Viscosity Measurements


Common Newtonian fluids:
(linear relationship between shear stress and shear rate)
Common non-Newtonian fluids:
(viscosity is not independent of shear rate)

  • Water
  • Mineral oils
  • Low concentration protein
  • Benzene
  • Ethanol
  • Shear Thinning
    • Polymer solutions
    • mAb solutions
    • Paints
  • Shear Thickening
    • Corn starch solution
    • wet sand
    • Silica suspension in PEG
  • Thixotropic
    • Yogurt
    • Gel
    • Clay
    • Colloids
  • Bingham Pseudoplastic
    • Ketchup
    • Mayonnaise
    • Lotion

 

shear rates

RheoSense viscometers are powered by our patented VROC® (Viscometer-Rheometer-on-a-Chip) technology. VROC combines microfluidic and MEMS (Micro-Electro-Mechanical Systems) technologies to measure dynamic viscosity over a wide dynamic range of operation, delivering data with the highest accuracy and repeatability. Compared to conventional viscometers and rheometers, RheoSense’s rectangular slit method viscometers (USP chapter 914) offer several advantages:

  • Small sample size requirement (26µL – 100µL)
  • Cost-effective
  • Characterization of both Newtonian & non-Newtonian fluids
  • Enable high shear rates without flow instabilities
  • Prevent evaporation and contamination of samples
  • Render high throughput due to a simple flow-through design

Learn more about how RheoSense’s VROC technology works here! If you’re ready to see our technology in action, contact us to schedule a free demo of any of our VROC powered viscometers!
Schedule a Free demoWritten by: Eden Reid, RheoSense Senior Marketing Associate