Rheology is the study of flow and deformation of materials under stress. There are two types of fluids - Newtonian fluids which follow a linear stress-strain relationship and non-Newtonian fluids which do not follow this relationship. Various types of non-Newtonian fluids exist such as plastic, pseudoplastic, dilatant, thixotropic and rheopectic fluids. Flow properties of fluids can be determined using viscometers such as capillary, rotating cylinder and cone plate viscometers. Rheology has applications in various areas including pharmaceuticals, cosmetics, food and construction materials.

2. RHEOLOGY
SUBMITTED BY
Mrs. Uzma Ali

3. GROUP MEMBER
Swaira Shafique
Neelum Haleema
Zahra Abbas
Maham Ahmad
Hina Shafique
Memoona Nasir

4. OUTLINE
• Definition
• Viscosity
• Newtonin fluid
• Non-Newtonin fluid
• Determination of flow properties
• Application

5. Rheology
• “ Rheology is concerned with the flow and
deformation of materials experiencing an
applied force.”

6. VISCOSITY
• “The viscosity of the fluid is the internal resistance or
friction involved in the relative motion of one
layer of molecules with respect to the next.”
• Unit:
 Unit of viscosity is poise.

7. Coefficient of viscosity
• “ Ratio of applied stress and rate of shear”
• If viscosity increase then shear stress increase:
Shear stress
Rate of shear

8. Classification of Materials According to
Flow and Deformation
• When classifying materials according to the types of
flow and deformation, it is customary to place them
in two categories.
• (i) Newtonian system
• (ii) Non-Newtonian system

9. Newtonian fluid
• Fluids which obey Newtonian equation is called
Newtonian fluid.

10. Shear stress
• “ Force per unit area ”
• S= F/A
• S= ᶯ du/dx
• =ᶯ S/du/dx
• =ᶯ F/A/du/dx
• This is Newtonian equation

11. Non-Newtonian fluid
• Fluids which not follow the Newtonian equation
• Because value of ᶯ varies with rate of shear
• Consider apparent viscosity of these system at
particular rates of shear
• Apparent viscosity is ratio of shear stress to shear rate
• Apparent viscosity is time dependent

12. Types of Non-Newtonian fuid

13. Plastic flow
• “ The material, which fails to flow until
a certain shearing stress has been applied.”
• Bingham Bodies:
 “The bodies, which follow the plastic flow,
are called as Bingham Bodies.”
• Yield Value:
 “The point at which curve intercept the
axis of shearing stress is called yield value.”

14. Plastic flow
• A Bingham body does not begin to flow until a
shearing stress, corresponding to the yield value
exceeded.
• ᶯpl= S-fb
• du/dx

15. Pseudoplastic flow
• “ Flow show by the materials having polymers in solutions.”
• Example are given as
• · Cellulose ether,· Tragacanth.· Alginates etc.
• There is no yield value so no part of the curve is linear.
• Viscosity:
 The viscosity of the pseudoplastic materials
deceases with the increase in the rate of shear
S =K du/dx n=1n

16. Dilatant flow
• A type of flow characterized by an increase in
viscosity as shear stress is increased
• Example is given as
• · Starch in cold water,· Deflocculated particles
• Apparent viscosity must increase with increase in
shear rate up to a maximum level
• S = K du/dx n=‹1n

17. Thixotropy
• To change by touch
• It is defined as a reversible transition from a gel to a
sol
• Bentonite gel is good example
Thixotrophy

18. Rheopexy
• Rheopexy is the rare property of some non-
Newtonian fluids to show a time-dependent increase
in viscosity; the longer the fluid undergoes shearing
force, the higher its viscosity.
• Time lag that
can be reduced
by a slow shaking
or rolling motion.
Rheopexy

19. Negative thixotropy
• Transformation of dilute concentration into viscous
concentration
• Occur due to gradual growth in molecular structures
over the time

20. Determination of flow properties
1) Capillary viscometer:
 Ostwald U-tube viscometer
 Suspended level viscometer
2) Rational viscometer
 Concentric cylinder viscometer
 Cone plate viscometer

21. Ostwald viscometer
• Work under influence of gravity
• Liquid is introduced through arm V
until G
• Pipette is used to avoid wetting of tube
above G
• Liquid is suck into arm W above E
• Time taken for falling E to F is noted
C
E
F
W
A
V
G

22. Suspended level viscometer
• Liquid is fill to bulb C through tube V
• Ventilating tube Z is then closed; liquid is
drawn into C by applying suction at W until
liquid is above mark E
• Liquid is held by closing W & Z is opened
• W is finally opened & time taken for falling
of liquid from E to F
• Associated with readjustment of volume when
measurement taken as series of temperature
V W Z
E
C
F
B
A

23. Poiseuille’s equation
 V/t = ᴫPr / 8ᶯ l
 V/t ∝ P/ᶯ
 P= hρg
 V/t ∝ hρg / ᶯ
 1/ t ∝ ρ / ᶯ
 V=ᶯ/ρ
 1/t ∝ 1/V
 t V∝
 V= ct
4
 Kinematic
viscosity
“The absolute viscosity
divided by the
density
of a liquid at definite
temperature.”

24. Concentric cylinder viscometer
• In which liquid whose viscosity is measured fills the
space between 2 coaxial cylinder, the inner one
suspended by torsion wire
• Outer cylinder is rotated at constant
rate & resulting torque on inner
cylinder is measured
• Inner cylinder is rotated at constant
rate & resulting torque on outer
cylinder is measured

25. Concentric cylinder viscometer
• C =4ᴫ hὠᶯ
• 1/ r1 – 1/r2
• C= Torsion constant
• h= height of inner cylinder
• = angular velocityὠ
• r1 & r2 = radius of outer and inner cylinder
2 2
θ

26. Disadvantages
• Shear rate not uniform throughout the process
• Frictional drags increase in temperature
• Cleaning difficult

27. Cone plate viscometer
• Plate is rotated at a fixed speed
• Torque transmitted through sample
to cone is measured
• Viscosity calculated from equation
• ᶯ = 3G/2ᴫR
Ω/Ψ
• G= torque on cone
• R= radius of cone
• Ω= radial velocity of plate
• Ψ = angle between cone and plate
2

28. Falling sphere viscometer
• 3ᴫᶯdu=ᴫ/6d g( ρ – ρ )
• Left side of equation shows
viscous drag
• Right side of equation shows
force of gravity
• Use for Newtonin fluid
• Temperature of falling sphere
and liquid is same
3
s 1

29. Falling sphere viscometer
• η= d g(ρ – ρ )
18 u V= η/ρ
• η/ρ= d g ( ρ – ρ )
18uρ1
• V= d g ( ρ – ρ ) F
18uρ
2
S 1
2
S 1
S 1
2
1

30. Red wood viscometer
• Involve determining the time taken for given volume of liquid
to flow through narrow orifice
• Redwood viscometer is an empirical instrument
• Efflux times are arbitrary measurement
of viscosities usually expressed
as Redwood seconds.

31. Application in Pharmacy
• It is involved in formulation and analysis of pharmaceutical
products as emulsions, paste, suppositories and tablet coatings.
• It is involved in manufacture of pastes medicines cream ointments.
• It is also involved in mixing and flow of materials and there
packing in containers.
• The poloxamers are block polymers and are used in dermatologic
bases or topical ophthalmic preparations because of their low
toxicity & ability to form clear water based gels.
• Also used in study of paints, inks, doughs, road building materials,
cosmetics, dairy products & other materials.