Rheology (1)

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Pharmaceutical Rheology
Unit II
By
Abhijit Debnath, Asst. Professor Faculty of
Pharmaceutical Sciences PDM University
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Outline of the Talk
? 1. Importance of Rheology Pharmacy and it
Applications ? 2. Introduction Definition and
fundamentals. Newton's laws Flow of Fluids ?
3. Types of Fluids Newtonian and Non-Newtonian
Fluids ? 4. Viscosity ? 5. Measurements of
viscosity ? 6. Instrumentation ? 7.
Viscoelasticity
3

• 1.
• Importance of Rheology Pharmacy Its
  Applications

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1. Importance of Rheology Pharmacy it
Applications
In pharmaceutical technology, rheological
measurements are involved in the following

1. Manufacturing of dosage forms Materials undergo
   process such as mixing, flowing through pipes,
   filling into the containers etc. Flow related
   changes influence the selection of mixing
   equipment.

2. Handling of drugs for administration The
syringibility of the medicines, the pouring of
the liquids from containers, extrusion of
ointment from tubes, all depend on the changes
in flow behavior of dosage forms.
3. Topical application of product onto skin
4. Physical stability of suspensions, emulsions
and semisolids
5. Bioavailability, since viscosity has been
shown to affect the absorption rate of drugs.
6. Release of drug from dosage forms and delivery
systems.
7. Formulation of medicinal and cosmetic creams,
pastes and lotions.
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1. Importance of Rheology Pharmacy it
Applications
8. Formulation of emulsions, suspensions,
suppositories, and tablet coating.
9. Fluidity of solutions for injection.
10. In mixing and flow of materials, their
packaging into the containers, their removal
prior to use, the pouring from the bottle.
11. Extrusion of a paste from a tube .
12. Passage of the liquid to a syringe needle.
13. Influence the choice of processing equipments
in the pharmaceutical system.
14. Can affect the patients acceptability of the
product, physical stability, biologic
availability, absorption rate of drugs in the
gastrointestinal tract.
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Outline of the Talk
? 1. Importance of Rheology Pharmacy and it
Applications ? 2. Introduction Definition and
fundamentals. Newton's laws Flow of Fluids ?
3. Types of Fluids Newtonian and Non-Newtonian
Fluids ? 4. Viscosity ? 5. Measurements of
viscosity ? 6. Instrumentation ? 7.
Viscoelasticity
7

• 2. Introduction

2.1 Rheology 2.2 Definition and
fundamentals. 2.3 Newton's laws
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21-Feb-16
2.1 Rheology

• rheo to flow
• logos science
• Rheology is the study of the flow and deformation
  of matter under stress.

• Rheology is the science/physics that concerns
  with the flow of liquids and the deformation of
  solids.
• Study of flow properties of liquids is important
  for pharmacist working in the manufacture of
  several dosage forms, viz., simple liquids,
  gels, ointments, creams, and pastes.
• These systems change their flow behaviour when
  exposed to different stress conditions

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21-Feb-16
2.2 Definition and fundamentals
1) Shear stress (t) is the component of stress
coplanar with a material cross section. Shear
stress arises from shear forces, which are pairs
of equal and opposing forces acting on opposite
sides of an object
2) Rate of Shear or Shear rate Shear rate is the
rate at which a progressive shearing deformation
is applied to some material.
3) Rheogram Plot of rate of shear as a function
of shear stress.
4) Viscogram Plot of rate of shear as a function
of viscosity.
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21-Feb-16
2.2 Definition and fundamentals
The deformation of matter under influence of
force or stress can be described by two
components namely (1) Elasticity and (2)
Viscosity.
1) Elasticity Elasticity is achieved if the
shape of the body is restored once the force is
withdrawn.
2) Viscosity Viscosity or pure viscous flow
occurs if there is continuous movement during the
applied force, and no restorative motion occurs
once the force is withdrawn.
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2.3 Newton's law of viscous flow
21-Feb-16
To understand the fundamental components of
viscous flow, just consider,

• Two parallel planes are a distance dx apart the
  viscous body is confined between the planes.
• When force, F, is applied the top, plane A. moves
  horizontally with a velocity dv but the lower
  plane B remains motionless.
• As a consequence, there exists a velocity
  gradient dv/dx between the planes.
• This velocity gradient over a distance is known
  as the rate of shear, D (dvldx).

• The horizontal force per unit area (P/A) creating
  the deformation is known as the shear stress, S
  (F/A). According to Newton's law of viscous flow

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2.4 Temperature Dependence of Viscosity
21-Feb-16

• Viscosity of liquids falls with rise in
  temperature,
• Whereas that of gases rises with rise in
  temperature.
• In liquids, the fall in viscosity is due to
  decrease in the intramolecular forces of
  attraction.
• The variation of viscosity with temperature is
  expressed by an equation analogous to the
  Arrhenius equation of chemical kinetics

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Outline of the Talk
? 1. Importance of Rheology Pharmacy and it
Applications ? 2. Introduction Definition and
fundamentals. Newton's laws Flow of Fluids ?
3. Types of Fluids Newtonian and Non-Newtonian
Fluids ? 4. Viscosity ? 5. Measurements of
viscosity ? 6. Instrumentation ? 7.
Viscoelasticity
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• 3. Types of Fluids

Newtonian
Non- Newtonian
Time dependent
Time Independent
Thixotropic
Plastic
Antithixotropic
Pseudoplastic
Rheopexy
Dilatant
Negative rheopexy
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3. Types of Fluids

• Based on Newton's law of viscous flow, fluids are
  classified as Newtonian and non-Newtonian.

• Fluids that follow Newton's law of viscous flow
  are called Newtonian fluids, whereas
  non-Newtonian fluids do not follow it.

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21-Feb-16
3.1 Newtonian Fluid
1. Simple liquids, either pure chemicals or
solutions of lower-molecular-weight compounds,
are Newtonian fluids in which a direct
proportionality exists, for all values of shear,
between shear stress and shear rate.
2. Viscosity of such fluids is independent of the
rate of shear but depends on composition,
pressure and temperature.
3. It can be seen in liquids and in solid
heterogeneous dispersions such as emulsions,
suspensions, colloids and ointments.
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3.1 Non-Newtonian Fluid
1. A non newtonian flow is defined as one for
which the relation between Shear of Stress and
Rate of Shear are not linear.
2. In other words when the shear rate is varied,
the shear stress is not varied in the same
proportion. The viscosity of such a system thus
varies as the shearing stress varies.
Non-Newtonian Fluid
1. Time Independent
2. Time Dependent
2.1 Thixotropic
1.1 Plastic
2.2 Antithixotropic
1.2 Pseudoplastic
2.3 Rheopexy
1.3 Dilatant
2.4 Negative rheopexy
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3.1 Non-Newtonian Fluid
1. A non newtonian flow is defined as one for
which the relation between Shear of Stress and
Rate of Shear are not linear.
The viscosity of the fluid is dependent on
temperature, shear rate and time.
These fluids instantaneously adapt to changing
shear stress
2. In other words when the shear rate is varied,
the shear stress is not varied in the same
proportion. The viscosity of such a system thus
varies as the shearing stress varies.
Non-Newtonian Fluid
1. Time Independent
2. Time dependent
2.1 Thixotropic
1.1 Plastic
2.2 Antithixotropic
1.2 Pseudoplastic
2.3 Rheopexy
1.3 Dilatant
2.4 Negative rheopexy
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3.1 Non-Newtonian Fluid
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3.1 Non-Newtonian Fluid
Non-Newtonian Fluid
1. Time Independent
2. Time dependent
2.1 Thixotropic
1.1 Plastic
1.1 Plastic
2.2 Antithixotropic
1.2 Pseudoplastic
2.3 Rheopexy
1.3 Dilatant
2.4 Negative rheopexy
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3.1 Non-Newtonian Fluid Plastic
1. Plastic materials or Bingham plastics require
an initial finite force, called yield value,
before any rheological flow can start.
2. At shear stress values below the yield value,
such plastic materials substances behave as
elastic solids exhibiting reversible deformation,
and above the yield value, they behave as
Newtonian systems.
3. Concentrated flocculated suspensions (e.g.
concentrated zinc oxide suspension) and semisolid
dosage forms, such as gels, creams and ointments,
are examples of plastic materials.

• EXAMPLES ZnO in mineral oil, certain pastes ,
  paints and ointments.

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3.1 Non-Newtonian Fluid
Non-Newtonian Fluid
1. Time Independent
2. Time dependent
2.1 Thixotropic
1.1 Plastic
2.2 Antithixotropic
1.2 Pseudoplastic
1.2 Pseudoplastic
2.3 Rheopexy
1.3 Dilatant
2.4 Negative rheopexy
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3.1 Non-Newtonian Fluid Pseudoplastic
1. Shear-thinning behaviour is often referred to
as pseudoplasticity.
2. Pseudoplastic material tends to become more
fluid the faster they are stirred.
3. The curve for a pseudoplastic material begins
at the origin (or at least approaches it at low
rates of shear).
4. The curved rheogram for pseudoplastic
materials is due to shearing action on the long
chain molecules of materials such as linear
polymers.

• EXAMPLES
• Weakly flocculated suspensions,
• Polymeric solutions such as solution of
  tragacanth,
• Methyl cellulose in water

• Sodium CMC in water
• Sodium alginate and cellulose derivatives' and
• Semisolid systems containing polymer component
  are examples of pseudoplastic materials

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3.1 Non-Newtonian Fluid
Non-Newtonian Fluid
1. Time Independent
2. Time dependent
2.1 Thixotropic
1.1 Plastic
2.2 Antithixotropic
1.2 Pseudoplastic
2.3 Rheopexy
1.3 Dilatant
1.3 Dilatant
2.4 Negative rheopexy
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3.1 Non-Newtonian Fluid Dilatant
1. Shear-thickening behaviour is often referred
to as dilatancy.
2. Materials that increase in volume, i.e.
dilate, when sheared are known as dilatant.
3. Suspensions containing high concentrations
(gt50 w/w) of small, deflocculated particles
exhibit dilatant behaviour. Flow properties of
dilatants are opposite to that of pseudoplastics.
4. Certain suspensions with a high percentage of
dispersed solids exhibit an resistance to flow
with increasing rate of shear.
5. Such systems actually increase in volume when
sheared are called dilatant. Dilatant
materials "shear thickening systems."
6. When the stress is removed, a dilatant system
returns to its original state of fluidity.
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3.1 Non-Newtonian Fluid
Non-Newtonian Fluid
1. Time Independent
2. Time dependent
2.1 Thixotropic
1.1 Plastic
2.2 Antithixotropic
1.2 Pseudoplastic
2.3 Rheopexy
1.3 Dilatant
2.4 Negative rheopexy
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3.1 Non-Newtonian Fluid
Non-Newtonian Fluid
1. Time Independent
2. Time dependent
2.1 Thixotropic
2.1 Thixotropic
1.1 Plastic
2.2 Antithixotropic
1.2 Pseudoplastic
2.3 Rheopexy
1.3 Dilatant
2.4 Negative rheopexy
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3.1 Non-Newtonian Fluid Thixotropic

• MEASUREMENT OF THIXOTROPHY
• The most apparent characteristics of thixotropic
  system is the Hysteresis loop formed by up curve
  down curves of the rheograms.
• The area of Hysteresis loop has been used to
  measure the thixotropic breakdown and can be
  obtained by means of Planimeter.
• With plastic (Bingham ) bodies two approaches
  are used to estimate degree of thixotrophy.

• It is defined as, isothermal and comparatively
  slow recovery on standing of material of a
  consistency lost through shearing.

• It is shear thinning system, when agitated and
  kept aside it is expected to return its original
  state of fluidity, but takes longer time to
  recover compared to the time taken for agitation.

• Thixotropic behaviour can be shown by plastic and
  pseudo plastic system.

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3.1 Non-Newtonian Fluid
Non-Newtonian Fluid
1. Time Independent
2. Time dependent
2.1 Thixotropic
1.1 Plastic
2.2 Antithixotropic
2.2 Antithixotropic
1.2 Pseudoplastic
2.3 Rheopexy
1.3 Dilatant
2.4 Negative rheopexy
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3.1 Non-Newtonian Fluid Antithixotropic

• Anti-thixotrophy represents an increase in
  consistency (high viscosity) rather decrease in
  consistency in the down curve.

• The increase in thickness or resistance to flow
  with increase time of shear observed or
  (magnesia magma).

• Anti thixotrophy is flocculated system
  containing low solid content (110 ).

• Dilatancy system is deflocculated system
  containing solid content ( gt 50 ).

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3.1 Non-Newtonian Fluid
Non-Newtonian Fluid
1. Time Independent
2. Time dependent
2.1 Thixotropic
1.1 Plastic
2.2 Antithixotropic
1.2 Pseudoplastic
2.3 Rheopexy
2.3 Rheopexy
1.3 Dilatant
2.4 Negative rheopexy
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3.1 Non-Newtonian Fluid Rheopexy

• Rheopexy is phenomena in which a sol forms a gel
  more readily when shaken or sheared than when
  allow to form the gel while the material is kept
  at rest.

• In rheopectic system, the gel is the equilibrium
  state.

• In anti thixotropic system, the sol is the
  equilibrium state.

e.g. Magnesia magma, Clay suspension
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3.1 Non-Newtonian Fluid Negative rheopexy

• Negative rheopexy is observed in antithixotropic
  systems where gentle vibration, shaking and mild
  turbulence speed up the reformation of solution
  from the gel state.

• In this, an antithixotropic system, such as
  magnesia magma, becomes more mobile under the
  influence of mild turbulence.

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Outline of the Talk
? 1. Importance of Rheology Pharmacy and it
Applications ? 2. Introduction Definition and
fundamentals. Newton's laws Flow of Fluids ?
3. Types of Fluids Newtonian and Non-Newtonian
Fluids ? 4. Viscosity ? 5. Measurements of
viscosity ? 6. Instrumentation ? 7.
Viscoelasticity
35

• 4. Viscosity

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4. Viscosity

• Why Viscosity is Important?

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4.1 Why Viscosity is Important?

• Measuring viscosity is a good way to discover the
  properties of matter.
• Testing the viscosity of materials is practiced
  in many other industries before packaging
  products.

• Examples
• If toothpaste has the wrong viscosity, a great
  amount of toothpaste will not flow out of the
  tube.
• The same applies for ointments. If they do not
  have the right thickness, they cannot be easily
  applied.
• The viscosity of creams and lotions may affect
  the rate of absorption of the products by the
  skin.
• A greater release of active ingredients is
  generally possible from the softer, less viscous
  bases.

• The viscosity of semi-solid products may affect
  absorption of these topical products due to the
  effect of viscosity on the rate of diffusion of
  the active ingredients.
• The rate of absorption of an ordinary suspension
  differs from thixotropic suspension.
• Thixotropy is useful in the formulation of
  pharmaceutical suspensions and emulsions. 

38
Outline of the Talk
? 1. Importance of Rheology Pharmacy and it
Applications ? 2. Introduction Definition and
fundamentals. Newton's laws Flow of Fluids ?
3. Types of Fluids Newtonian and Non-Newtonian
Fluids ? 4. Viscosity ? 5. Measurements of
viscosity ? 6. Instrumentation ? 7.
Viscoelasticity
39

• 5. Measurements of viscosity

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5. Measurements of viscosity

• Based on the Material to be analysed and/or type
  of the Rheogram obtained

• Based on the Principle of measuring viscosity

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5. Measurements of viscosity

• Based on the Material to be analysed and/or type
  of the Rheogram obtained

• Based on the Material to be analysed and/or type
  of the Rheogram obtained

• Based on the Principle of measuring viscosity

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5. Measurements of viscosity

• Based on the Material to be analysed and/or type
  of the Rheogram obtained

• Based on the Principle of measuring viscosity

Capillary viscometers Density-dependent viscometers Rotational viscometers
They are based on the rate of flow of a liquid through a fine capillary or an orifice. They are based on the velocity of a falling object through a liquid under the influence of gravity. They are based on the resistance of a rotating element in contact with or immersed in the liquid.
Ostwald Viscometer Ubbelohed Suspended Level Viscometer Extrusion rheometer Falling Sphere Viscometer Bubble Viscometer Cup Bob Viscometer Cone Plate Viscometer
43
Outline of the Talk
? 1. Importance of Rheology Pharmacy and it
Applications ? 2. Introduction Definition and
fundamentals. Newton's laws Flow of Fluids ?
3. Types of Fluids Newtonian and Non-Newtonian
Fluids ? 4. Viscosity ? 5. Measurements of
viscosity ? 6. Instrumentation ? 7.
Viscoelasticity
44

• 6. Instrumentation

45
6. Instrumentation

• Based on the Principle of measuring viscosity

Capillary viscometers Density-dependent viscometers Rotational viscometers
Ostwald Viscometer Ubbelohed Suspended Level Viscometer Extrusion rheometer Falling Sphere Viscometer Bubble Viscometer Cup Bob Viscometer Cone Plate Viscometer
46
6. Instrumentation

• Based on the Principle of measuring viscosity

Capillary viscometers Density-dependent viscometers Rotational viscometers
Ostwald Viscometer Ubbelohed Suspended Level Viscometer Extrusion rheometer Falling Sphere Viscometer Bubble Viscometer Cup Bob Viscometer Cone Plate Viscometer
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6. Instrumentation Ostwald Viscometer
Ubbelohed Suspended Level Viscometer

• Ostwald viscometer is used to determine the
  viscosity of a Newtonian liquid. Both dynamic
  and kinematic viscosities can be obtained.
• When a liquid flows by gravity, the time required
  for the liquid to pass between two marks (A and
  B shown in Figure) through a vertical capillary
  tube is determined.

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6. Instrumentation

• Based on the Principle of measuring viscosity

Capillary viscometers Density-dependent viscometers Rotational viscometers
Ostwald Viscometer Ubbelohed Suspended Level Viscometer Extrusion rheometer Falling Sphere Viscometer Bubble Viscometer Cup Bob Viscometer Cone Plate Viscometer
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6. Instrumentation Extrusion rheometer
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6. Instrumentation

• Based on the Principle of measuring viscosity

Capillary viscometers Density-dependent viscometers Rotational viscometers
Ostwald Viscometer Ubbelohed Suspended Level Viscometer Extrusion rheometer Falling Sphere Viscometer Bubble Viscometer Cup Bob Viscometer Cone Plate Viscometer
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6. Instrumentation Falling Sphere Viscometer

• The sample ball are placed in the inner glass
  tube allowed to reach temperature equilibrium
  with the water in the surrounding constant
  temperature jacket.
• The tube jacket are then inverted, which
  effectively places the ball at the top of the
  inner glass tube.
• The time for the ball to fall between two marks
  is accurately measured repeated several times.

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6. Instrumentation

• Based on the Principle of measuring viscosity

Capillary viscometers Density-dependent viscometers Rotational viscometers
Ostwald Viscometer Ubbelohed Suspended Level Viscometer Extrusion rheometer Falling Sphere Viscometer Bubble Viscometer Cup Bob Viscometer Cone Plate Viscometer
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6. Instrumentation Cup Bob Viscometer

• This is a multipoint viscometer and belongs to
  the category of rotational viscometers.
• The sample is placed in the cup and the bob is
  placed in the cup up-to an appropriate height.

• The sample is accommodated between the gap of cup
  and bob.
• Cup or bob is made to rotate and the torque
  (shearing stress) from the viscous drag is
  measured by a spring or sensor in the drive of
  the bob.

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6. Instrumentation Cup Bob Viscometer
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6. Instrumentation

• Based on the Principle of measuring viscosity

Capillary viscometers Density-dependent viscometers Rotational viscometers
Ostwald Viscometer Ubbelohed Suspended Level Viscometer Extrusion rheometer Falling Sphere Viscometer Bubble Viscometer Cup Bob Viscometer Cone Plate Viscometer
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6. Instrumentation Cone Plate Viscometer

• The sample is placed at the center of the plate
  which is then raised into position under the
  cone.
• The cone is driven by a variable speed motor
  the sample is sheared in the narrow gap between
  the stationary plate and the rotating cone.
• The rate of shear in rev./min. is increased
  decreased by a selector dial the torque
  (shearing stress) produced on the cone is read
  on the indicator scale.

• A plot of rpm or rate of shear versus scale
  reading (shearing stress) may be plotted.

57
Outline of the Talk
? 1. Importance of Rheology Pharmacy and it
Applications ? 2. Introduction Definition and
fundamentals. Newton's laws Flow of Fluids ?
3. Types of Fluids Newtonian and Non-Newtonian
Fluids ? 4. Viscosity ? 5. Measurements of
viscosity ? 6. Instrumentation ? 7.
Viscoelasticity
58

• 7. Viscoelasticity

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7. Viscoelasticity
1. Viscoelastic materials exhibit both viscous
fluidity and elastic solidity when undergoing
deformation.
2. Viscoelastic property is exhibited by most
pharmaceutical semisolids such as creams,
lotions, ointments, colloidal dispersions and
suppositories.
2. Viscoelastic property is exhibited by most
pharmaceutical semisolids such as creams,
lotions, ointments, colloidal dispersions and
suppositories.

• Viscous materials resist shear flow and strain
  linearly with time when a stress is applied.
• Elastic materials strain instantaneously when
  stress is applied and quickly return to their
  original state on removal of stress.
• Viscoelastic materials exhibit both pure viscous
  flow and elastic deformation. Such behaviour is
  called viscoelastic flow.

3. Amorphous and semicrystalline polymers,
carbopol gel and aqueous solution of high
molecular weight poly(ethylene oxide) also
exhibit viscoelasticity.
4. Biological fluids such as blood, sputum and
cervical fluid also exhibit viscoelasticity.
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Outline of the Talk
? 1. Importance of Rheology Pharmacy and it
Applications ? 2. Introduction Definition and
fundamentals. Newton's laws Flow of Fluids ?
3. Types of Fluids Newtonian and Non-Newtonian
Fluids ? 4. Viscosity ? 5. Measurements of
viscosity ? 6. Instrumentation ? 7.
Viscoelasticity
61
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