Pharmaceutical Rheology

Unit II

By

Abhijit Debnath, Asst. Professor Faculty of

Pharmaceutical Sciences PDM University

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

- 1.
- Importance of Rheology Pharmacy Its

Applications

1. Importance of Rheology Pharmacy it

Applications

In pharmaceutical technology, rheological

measurements are involved in the following

- 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.

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.

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

- 2. Introduction

2.1 Rheology 2.2 Definition and

fundamentals. 2.3 Newton's laws

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

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.

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.

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

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

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. Types of Fluids

Newtonian

Non- Newtonian

Time dependent

Time Independent

Thixotropic

Plastic

Antithixotropic

Pseudoplastic

Rheopexy

Dilatant

Negative rheopexy

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.

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.

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

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

3.1 Non-Newtonian Fluid

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

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.

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

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

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

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.

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

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

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.

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

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 ).

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

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

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.

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

- 4. Viscosity

4. Viscosity

- Why Viscosity is Important?

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.

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

- 5. Measurements of viscosity

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

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

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

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

- 6. Instrumentation

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

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

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.

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

6. Instrumentation Extrusion rheometer

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

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.

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

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.

6. Instrumentation Cup Bob Viscometer

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

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.

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. Viscoelasticity

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.

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

Thank You

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