This document provides an overview of rheology, which is the study of flow and deformation of materials. It discusses different types of fluid flow including Newtonian, plastic, pseudoplastic and dilatant flow. Key concepts covered include viscosity, shear stress, rate of shear, and factors affecting viscosity. Various rheological measurement techniques are described such as capillary viscometry, falling sphere viscometry, and rotational viscometry. The document also discusses non-Newtonian flow properties including thixotropy, hysteresis, and the Heckel equation.

1. Presentation
on
RHEOLOGY
Presented By: Ms. Sarika S. Suryawanshi
M. Pharm Pharmaceutics
Associate Professor
Ashokrao Mane College of Pharmacy, Peth
Vadgaon

2.  Introduction:
 Rheo – to flow
 logos – science
 Resistance to flow of liquid & deformation of
solid
 Used in simple liquids, ointments, cream,
pastes
 Change in flow behavior under stress
condition
1. Manufacturing of dosage forms: mixing,
flowing through pipes, filling into containers
II. Handling of Drugs for administration: pouring
from the bottle, extrusion from a tube or a
passage of the liquid to a syringe needle

3.  Concept of viscosity
 Shear stress: Force per unit area which
applied to bring the flow.
 Shear Stress F= F’/A
 Rate of shear: change in velocity, dv
with infinite change in distance, dr
 Rate of shear G = dv/dr
 Higher viscosity, greater force per unit
area required to produce rate of shear.
 F=nG
 n= coefficient of viscosity
 Centipoise, cp= 0.01 P
 CGS:dy.sec/cm2

4.  Factors:
 Intrinsic Factors
1. Molecular weight: Higher molecular
weight , higher viscosity
2. Large & irregular shape particles
more viscous than regular shape
3. Intermolecular interaction: stronger,
particles stick to each other
enhances viscosity

5.  Extrinsic Factors
 Pressure: enhances cohesive forces
 Addition of nonelectrolytes: increases
 Polymers
 Strong electrolytes: Decreases, alkali
metal
 Temperature: breaking of cohesive
forces leads to decrease viscosity

6.  Determination of flow properties
 Capillary Viscometer
 Falling sphere viscometer
At a Single rate of shear one point on the
curve
 Newtonian fluids
 Cup & Bob
 Cone & Plate
 Rate of shear many points on the curve
 Both

7. Ostwald Viscometer
n1 = ρ1t1/ ρ2t2 X n2
ρ1- density of unknown liquid
t1- time of flow of unknown
liquid
n2- viscosity of known liquid
Applications
1. Quality control purpose in
formulation & evaluation of
dispersed system
2. Evolution of liquid paraffin,
dextran 40 injection

9.  Based on Hoeppler vicometer
 Glass tube placed vertically
 Constant temperature jacket for water
circulation is arranged around glass tube
 Steel / glass ball dropped & allowed to reach
equilibrium with temp of outer jacket
 Invert tube with jacket
 Note time taken for the ball to fall between two
marks
 Newtonian liquids
 n1= t(Sb - Sf) B
 Sb & Sf- specific gravity of ball & fluid
 0.5-200000 poise
 NLT 30 sec

11.  Rotational viscometer
 Bob rotatory
 No. of rpm & torque represents rate of
shear & shearing stress rsp.
 Pseudoplastic system-
 n= Kv W/v
 W- shearing stress
 V- rpm
 n- viscosity
 Kv- contant

12.  Plug flow
 Bob exert pressure on inner wall of cup
 Use largest bob to reduce gap
 Increase speed of bob
Cone & Plate
 Plug flow can not be observed
 0.1- 0.2 ml sample
 Cleaning & filling easy
 Less time required

13. Newtonian flow
n= C T/v
T= torque
V= speed
Plastic flow
U= Cf T- Tf/v

14. Brookfield viscometer

15. Types of Flow
Newtonian (Newtonian Law of Flow)
 Liquid obeys Newton’s law
 F= nG
 Shear stress & rate of shear in the form
curve called rheogram or consistancy curve
 Rheogram passes through origin & slope
gives the coefficient of viscosity
 In a Newtonian fluid, the relation between the
shear stress and the strain rate is linear
 Eg: water, glycerin, solution of syrup

17.  Non-Newtonian
 Does not fallows Newton's law
 Many polymer solutions and ketchup,
starch suspensions, paint, blood and
shampoo.
 Plastic
 Pseudoplastic
 Dilatant

18. Plastic
 Curve doesn't pass through the origin.
 Substance initially behaves like an elastic body &
fails to flow when less amount of stress is applied.
 Further increase in shear stress leads to nonlinear
portion get linear
 Linear portion extrapolated intersects the X axis at
the point called yield point
 flocculated particles in suspensions, butter, pastes,
gel
 Yield value represents stress required to break the
inter particle contact so particle behave individually.
 Once stress is increases with rate of shear

19.  Material shows plastic flow called Bingham
bodies
 Slope = mobility & reciprocal is called
plastic flow
 U= F-f/ G
 F= hear stress
 F= yield value
 G= rate of shear

21. Pseudoplastic Flow
 Curve begins at origin (nearly zero at lower shear
stress)
 Stress increase with rate of shear but it is nonlinear
 Polymers in water such as tragacanth, sodium
alginate, methylcellulose

23. Dilatant Flow
 Enhances resistance of flow with increasing rate of
shear
 Volume increases , so called dilatant
 Shear thickening
 Stress is removed system returns to initial state
 Suspension containing high-concentration of small
deflocculated particles
 Suspension of starch
 Zinc oxide 30% in water

24.  At rest, molecules are closely packed,
minimum void space, amount of vehicle is
sufficient to fill void space.
 When shear stress is applied particles are
open or expands / dilatants
 Increases void space, insufficient fluid,
particle not wetted, slows paste like
consistancy
 F N = nG
 N is higher than 1

26. THIXOTROPY

27.  Hysteresis loop
 Up & down curves of thixotropic system
 Region between curves for the increasing &
decreasing shear rate ramps
 The area of Hysteresis is a measurement of
thixotropic breakdown.
 Shearing rate of plastic thixotropic material is
increased at constant rate from point a –b then
decreased at same rate at point e.
 Connectivity gives formation of Hysteresis loop abe
 Staring from point a if sample on application of
shear taken to point b & if at this point shear rate is
held constant for some time , t1 sec then depending
upon extent of time of shear

28.  Rate of shear & degree of sample structure it
shows reduction in shearing stress & hence
consistency of material.
 Further decrease in shear rate results in
formation of Hysteresis loop abce
 If sample held at constant rate of shear at
point (b) for some extended time t2 sec, loop
abcde is observered
 So, rheogram of thixotropic material is not
unique but it depends upon sample &
material

29.  Rheological property depends on rate at
which shear is increased or decreased &
length of time for which material is subjected
to any rate of shear.
 Procaine penicillin suspension in water

30.  Bulges
 Swell in presence of water gives bulges
 Conc aq solution of bentonite gel
(magma) 10-15 % gives hysteresis loop
with bulge in up curve
 Due to formation of some specific str of
crystalline plates of bentonite which
leads to swelling of magma.
 Swelled 3D str responsible for bulge in
up curve

31.  Spurs
 Highly structured material such as
parenteral solution (Procaine penicillin
gel for injection in 2% cmc solution) ,
buldged curve develops like spur
 Due to sharp structural breakdown
when taken into syringe needle
 Complex str exhibits high yield value
called spur value in up curve
 This value represents sharp point of
structural breakdown at low shear rate

32.  Negative thixotropy
 Negative thixotropy Known as anti
thixotropy which represents time
dependant increasing apparent viscosity
rather than decrease on application of
shearing stress.
 This is called sol to gel
 At resting consists of large number of
individual particles and small size
floccules
 When the system is sheared the
molecules of dispersed phase colloids
 Increase in collision frequency of these

33.  At equilibrium state very small number of
large floccules exists therefore system
exhibits sol form.
 Again when system is at rest large size
floccules breakup and gradually returns
to original state of small size floccules
and individual particles.
 It contains 1-10% of solid, dilatant
system are deflocculated containing
more than 50%by volume of solid.

34.  Observed in magnesium magma
 It was observed that when magnesium
magma was sheared with alternatively
first by increasing then decreasing
shear rates, it continuously get
thickened.
 With continuation of cycle the extent
of thickening reduces gradually then
reaches to equilibrium State.

35.  Rheopexy
 Sol transforms to a gel more readily
after it has been deformed by gentle
shaking and regular rolling and rocking
movements.
 Rheopexy is analogous to rheopexy and
fluids behavior called rheopectic
 It provides a mild turbulence which helps
the dispersed particles to get
themselves in random alignment to re-
establish gel structure.
 Used in plastic and pseudo plastic
system

36.  Measurements of thixotropy
 Thixotropic measurements of plastic
and pseudo plastic system can be
achieved by use of hysteresis loop
formed during thixotropic breakdown
of the system.
 Degree of thixotropy obtained by..
 1. Structural breakdown with time at
constant rate of shear
 2. Structural breakdown with time at
two different rates of shear

37.  Importance
 Desirable property in emulsion,
suspension, cream, ointment, pastes,
parenteral suspension for depot therapy.
 On storage gel on shaking sol.so poured
out easily.
 Helpful in improving stability of
thixotropic pharmaceutical system.
 Greater thixotropy higher physical
stability.
 Speardability of cream and ointment can
be corrected with thixotropic property


38.  Pouring of lotions from container , shape
of cream in container, extrusion of paste
from tube shows high thixotropic
property.
 T agents: bentonite, kaolin
microcrystalline cellulose for viscosity
which obstruct sedimentation and
creaming.
 Degree of thixotropy may change over
period time. So plastic viscosity, spur
value yield value are important
parameters.

39.  Deformation of solid
 Deformation change in size and shape of
object changing dimensions
 Stress
 Force per unit area that applies to object to
deform it unit Nm-2 or Pa
 Types
 1. Direct stress
 It is produced under direct loading conditions
 1Tensile stress
 Tensile force acting per unit area of the body
 Extension or elongate dimensions of the body
 Ratio of change in length to original length

40.  2. Compressive stress
 Compressive force acting per unit area of the
body
 Forces applied is opposite to each other
 Compress the dimensions
 3. Shear stress
 Shear force acting per unit area of the body
 Due to this body develops some resistive
force which is parallel to each surface but
opposite to direction of force applied
 2. Indirect stress
 Due to torque produced in the body
 3.combined stress
 Combination of above two types of stress

41.  Strain
 Measure the amount of deformation
 If bar has original length L and load is
applied on bar length of bar will change
∆L
Strain =∆L/L
 Types
 1. Tensile strain
 Ratio of increase in length to original
length of bar
 2. Compressive strain: Ratio. Of
decrease in length to original length of
bar

42.  Elastic modulus
 Ratio of stress/strain
 The constant of proportionality depends on
the Material being deformed and nature of
the deformation.
 Determine amount of force required per unit
deformation.

43.  Hooke's Law
 In an elastic member stress is directly
proportional to strain within elastic limit
 N/m2
 Young's modulus used to identify how much
the Material is elastic
 Elastic limit maximum stress that Nan be
applied to the substance before it deforms
permanently.
 Initial strain strain curve is straight line.
 Stress increases, curve is no longer straight.

44.  Stress exceeds the elastic limit, object
is permanently distorted and does not
return to its original shape after stress
is removed.
 Hence shape of the object is
permanently changed.
 As stress increases even further
material ultimately breaks

45.  Heckel equation
 From tablet dosage form we can understand
deformation behaviour of individual components
 Useful method for estimating the volume reduction
under the compression pressure in pharmacy.
 Plot can be affected by time of compression, degree
of lubrication and size of die.
 In [1/1D]=KP +A
 Kuentz and Leuenberger modified Rule which explain
transition between state of powder to state of tablet
 Hersey and Rees , York and Pilpel differentiate
powders into 3 types
 Types A
 Material comparatively soft, readily undergoes plastic
deformation.
 Sodium chloride

46.  Type B
 Initial curve region followed by a straight line.
 Harder material having higher yield pressure
 Lactose
 Types C
 Initial steep linear region which become
superimposed and flattened out as applied pressure
is increased
 Significance
 Used to characterize single material and also for
powder
 Two regions of plot I type B material represents the
initial repacking stage and subsequent deformation
process
 Crushing strength of tablets is correlated with values
of K of plot