WHAT ARE NEWTONIAN AND NON-NEWTONIAN FLUIDS?

Newtonian fluid, non Newtonian fluid, rheopectic, thixotropic, dilatant... what's the difference between these liquid properties? More importantly, what does it matter?

One thing is clear and easy to understand.

Newton the great is behind Newtonian fluid, non Newtonian fluid.

NEWTONIAN FLUIDS

A Newtonian fluid's viscosity remains constant, no matter the amount of shear applied for a constant temperature. These fluids have a linear relationship between viscosity and shear stress.

Examples:

• Water
• Mineral oil
• Gasoline
• Alcohol

NON-NEWTONIAN FLUIDS

You can probably guess that non-Newtonian fluids are the opposite of Newtonian fluids. 

When shear is applied, the viscosity of non-Newtonian fluids decreases or increases, depending on the fluid. The behavior of the fluid can be described in one of four ways:

• Dilatant - Viscosity of the fluid increases when shear is applied. 
• 
  
• For example:
  • Quicksand
  • Cornflour and water
  • Silly putty
  • 
    
• Pseudoplastic - Pseudoplastic is the opposite of dilatant; the more shear applied, the less viscous it becomes. For example:
  • Ketchup

• Rheopectic - Rheopectic is very similar to dilatant in that when shear is applied, viscosity increases. The difference here is that viscosity increase is time-dependent. For example:
  • Gypsum paste
  • Cream
  • 
    
• Thixotropic - Fluids with thixotropic properties decrease in viscosity when shear is applied. This is a time-dependent property as well. For example:
  
  • Paint
  • Cosmetics
  • Asphalt
  • Glue