Newtonian and non-Newtonian fluids can be classified based on their viscosity properties. Newtonian fluids have constant viscosity regardless of shear rate or stress. Non-Newtonian fluids have variable viscosity depending on factors like shear rate, stress over time, or prior deformation history. There are several types of non-Newtonian fluids including shear thinning, dilatant, Bingham plastic, thixotropic, and rheopectic fluids. Examples of non-Newtonian behaviors include ketchup becoming thinner with shaking and whipped cream increasing in viscosity over time. The document provides definitions and examples of different fluid types based on their viscosity characteristics.

1. Newtonian And Non- Newtonian
Fluids
Prepared by
PREETI MAURYA

2. What is fluid
• A fluid is a state of matter in which its molecules move freely.
• A fluid is a substance that continually flows under an applied shear stress.
Fluids can be classified as
Types of Fluid
Ideal Fluid
Real Fluid
Newtonian Fluid
Non-Newtonian Fluid
Compressible Fluid
Incompressible Fluid
Ideal Plastics fluid

3. Continued….
• Ideal fluid: A fluid, which is incompressible and having no viscosity, is known as an ideal fluid.
Ideal fluid is only an imaginary fluid as all the fluids, which exist, have some viscosity.
• Real fluid: Real fluid can be defined as the fluid which deforms continuously for certain amount
of shear stress and it consists of viscosity. Example : Water, Air etc.
• Ideal plastic fluid: A fluid, in which shear stress is more than the yield value and shear stress
is proportional to the rate of shear strain or velocity gradient, is known as ideal plastic fluid.
• Incompressible fluid: A fluid, in which the density of fluid does not change which change in
external force or pressure, is known as incompressible fluid. All liquid are considered in this
category.
• Compressible fluid: A fluid, in which the density of fluid changes while change in external
force or pressure, is known as compressible fluid. All gases are considered in this category.

4. Introduction
• Viscosity of a polymer solution depends on concentration and size (i.e., molecular weight) of the
dissolved polymer.
• By measuring the solution viscosity we should be able to get an idea about molecular weight.
Viscosity techniques are very popular because they are experimentally simple.
• They are, however less accurate and the determined molecular weight, the viscosity average
molecular weight, is less precise.
• For example, Mv depends on a parameter which depends on the solvent used to measure the
viscosity.

5. What is Viscosity
• Viscosity is a measure of a fluid's resistance to flow. OR
• The viscosity of a fluid is a measure of its resistance to deformation at a given rate.
• Viscosity is a measure of the internal friction of a fluid.
i. Molasses is highly viscous
ii. Water is low viscous
Low Viscous
High Viscous
Fig. 1

6. Continued….
Formula of Viscosity :-
Units – Pa.s , mPa.s, Poise (P), kg·m−1·s−1
Shear Stress(τ) :- Shear stress is define as force per unit area OR Shear stress, force tending to cause
deformation of a material by slippage along a plane or planes parallel to the imposed stress.
Unit - N/m² or Pa
Fig. 2
Viscosity (η) = Shear Stress(τ) Shear Rate(ϒ)

7. Continued….
Shear Rate( ϒ) :- Shear rate is the measure of the speed at which the intermediate layers moves
with respect to each other.
Unit - Sec⁻¹.
Where, v = velocity and dx = relative distance of layers.
Types of Viscosity
a) Dynamic Viscosity
b) Kinematic Viscosity.
Factor affecting Polymer Viscosity
I. Temperature
II. Concentration
III. Molecular weight
IV. And shear rate.
ϒ = dv/dx

8. Newtonian Fluid
• A fluid, whose viscosity does not change with the rate of deformation of shear stain. OR
• A fluid which obeys Newson's law of viscosity is termed as Newtonian fluid. OR
• Fluid flow which the shear stress is linearly proportional to the shear rate. OR
• Fluid have a constant viscosity at a given temperature. For these fluid , the viscosity is
independent of the shear stress rate change.
• A shear diagram for Newtonian fluid is shown below. Note that the slope is constant.
Fig. - 3 Fig. - 4
Shearstress
Shear rate
Newtonian Fluid
Viscosity
Shear rate
Newtonian Fluid

9. Continued….
Newton’s law viscosity
Where,
μ = Viscosity
τ = Shear stress (F/A)
du/dy = rate of shear deformation.
Examples – Water, Mineral oil, Gasoline, Alcohol, Ethyl alcohol, Hexane
Fig.- 5 Fig.- 6
τ = μ du/dy

10. Non – Newtonian Fluid
• When the ratio of shear stress to shear strain is variable or not constant. Other words, the
variation in shear rate and shear stress is not proportional. OR
• A fluid which does not obeys Newton's law of viscosity is termed as Non - Newtonian fluid.
• In reality most fluids are non-Newtonian, which means that their viscosity is dependent on shear
rate (Shear Thinning or Thickening) or the deformation history (Thixotropic fluids).
Examples – Plastics, Ketchup, Blood, Toothpaste, Yogurt.
Fig.- 7 Fig.- 8 Fig.- 9

11. Classification Non-Newtonian fluid
Non- Newtonian Fluid
Time Independent
• Pseudo plastics
• Dilatant
• Bingham plastics
Time Dependent
• Thixotropic
• Rheopectic

12. Time Independent Non-Newtonian fluid
Pseudo plastics(Shear Thinning) : Fluid displays a decreasing viscosity with an increasing
shear rate. This type of behaviour is called shear-thinning. OR
• A fluid whose apparent viscosity or consistency decreases instantaneously with an increase in
shear rate
• Examples : Plastics melts, Polymer solution, Printing ink blood etc.
Fig.- 10 Fig.- 11
Shear Rate
ShearStress
Viscosity
Shear Rate

13. Continued….
• Most polymer solution and melts exhibit shear thinning (Pseudoplastic), Whereas shear
thickening (Dilatant) behaviour is rarely observed.
• The observed shear thinning polymer melts and solutions is caused by disentanglement of
polymer chains during flow.
• Polymers with a sufficiently high molecular weight are always entangled and randomly oriented
when at rest.
• When sheared, however, they begin to disentangle and to align which causes the viscosity to
drop.
• The degree of disentanglement will depend on the shear rate.
• At sufficiently high shear rates the polymers will be completely disentangled and fully aligned.
• In this regime, the viscosity of the polymer melt or solution will be independent of the shear rate,
i.e. the polymer will behave like a Newtonian liquid again.
• The same is true for very low shear rates; the polymer chains move so slowly that entanglement
does not impede the shear flow. The viscosity at infinite slow shear is called zero shear rate
viscosity (η0).

14. Dilatant ( Shear Thickening)
• The rheological behaviour of dilatant (Shear thickening) fluid is exactly opposite to that of
pseudoplastic fluid, their viscosity increases with the rate of shear.
• Some liquids with dilatant behaviour are slurries, candy compounds, and corn-starch & water
mixtures.
Fig.- 12 Fig.- 13
Shear Rate
ShearStress
Viscosity
Shear Rate

15. Continued….
Fig.- 14 Fig.- 15
Pseudoplastic & Dilatant
Viscosity
Shear Rate
Newtonian Fluid
ShearStress
Shear Rate

16. Current and Future Applications of Dilatants
• Materials and Fluids that exhibit Non-Newtonian behaviour such as Dilatants offer a diverse range
of potential opportunities and future applications.
• Potential Applications of Dilatants:
• Shock absorption Systems
• Automotive Suspension - Magnetic particles suspended
• Impact Stress Cushioning - Sport / Athletics
• Accident damage and injury mitigation - Transport
• Impulse Distribution Systems
• Smart Body Armour

17. Bingham Plastic Fluid
• These fluids do not flow unless the stress applied exceeds a certain minimum value. Beyond a
minimum value of shear stress, a Bingham body shows a linear relationship between stress and
strain.
• Bingham plastic is a material that behaves as rigid body at low stresses but flows as a viscous fluid
at high stress.
• This behaviour is exhibited by slurries, suspensions of solids in liquids, paints, emulsions, foams,
blood, ketchup, tooth paste,etc.
Low shear High shear
Fig.- 16 Fig.-17
ShearStress
Shear Rate

18. Shear stress and deformation rate relationship of different fluids
Fig.- 18
ShearStress
Shear Rate

19. Time Dependent Fluid
• The time dependant fluid are those fluids, which show either a decrease or increase in the
viscosity with time at a particular shear rate.
• If these fluid are subjected to a constant shear rate, the shear stress will either decrease or
increase.
• These fluids are classified as thixotropic ( if viscosity decreases with time ) and rheopectic ( if
viscosity increases with time ) respectively.

20. Thixotropic Fluid
• The apparent viscosity decrease with time .Result break down in the microstructure of the
material as shearing continues.
• When at a constant shear rate, the stress decreases over a period of time due to structure
breakdown until eventually it reaches a steady value, the product is said to be thixotropic.
Examples : Aged condensed milk, cream and ice cream mix, egg white, paint, iron oxide gels etc.
Rheopectic Fluid
• Rheopectic liquids increase in viscosity as stress over time increases OR .
• This essentially the opposite of thixotropic behaviour, in which the fluid viscosity increases with
time as it is sheared at a constant rate.
• Rheopectic fluid are rarely encountered. Both thixotropic and rheopectic may occur in
combination with any of the previously discussed flow behaviour, or only at certain shear rates.
Examples : Printer ink, gypsum paste.

21. Continued….
Fig.- 19 Fig.- 20
Viscosity
Stress Over time
Rheopectic
Thixotropic
Thixotropic
Rheopectic
Shear Rate
ShearStress

22. The table below summaries four types of non-Newtonian fluids
Type of behaviour Description Example
Thixotropic Viscosity decreases with stress
over time
Honey – keep stirring, and solid
honey becomes liquid
Rheopectic Viscosity increases with stress
over time
Cream – the longer you whip it
the thicker it gets
Shear thinning Viscosity decreases with
increased stress Tomato sauce
Dilatant or shear thickening Viscosity increases with
increased stress
Corn-starch

23. Thank You