The rheology of different fluids is explained in details with graph

1. RHEOLOGY
OF FLUIDS
BY: VVIIDDHHII DDOOSSHHII

2. RHEOLOGY
rheo – to flow
logos – science
ology – the study of
Thus, rheology is the science that
concerns with the flow of liquids
and deformation of solids.

3. The study of viscosity is of true liquids,
solutions, dilute and concentrated colloidal
systems.
It is involved in the mixing and flow of
materials, their packaging into containers, the
pouring from the bottle, extrusion from a tube or
a passage of the liquid to a syringe needle.
It can affect the patient’s acceptability of the
product, physical stability, biologic availability,
absorption rate of drugs in the gastrointestinal
tract.
It influence the choice of processing
equipments in the pharmaceutical system

4. TWO CATEGORIES OF FLOW
& DEFORMATION
Newtonian ((NNeewwttoonniiaann LLaaww ooff FFllooww))
“the higher the viscosity of a liquid, the greater is
the force per unit area (shearing stress) required
to produce a certain rate of shear”
Shear – is a stress which is applied parallel or
tangential to a face of a material, as opposed to a
normal stress which is applied perpendicularly.
Shear stress
Measured in (SI unit): pascal
Commonly used symbols: τ
Expressed in other quantities: τ = F / A

5. A shear stress, is
applied to the top of
the square while the
bottom is held in
place. This stress
results in a strain, or
deformation,
changing the square
into a parallelogram.

6. A Newtonian fluid (named for Isaac Newton) is a fluid
whose stress versus rate of strain curve is linear and
passes through the origin. The constant of
proportionality is known as the viscosity.

7. In common terms, this means the fluid continues
to flow, regardless of the forces acting on it. For
example, water is Newtonian, because it continues
to exemplify fluid properties no matter how fast it is
stirred or mixed.
For a Newtonian fluid, the viscosity, by
definition, depends only on temperature and
pressure (and also the chemical composition of the
fluid if the fluid is not a pure substance), not on the
forces acting upon it.

8. NNoonn--NNeewwttoonniiaann
AA nnoonn--NNeewwttoonniiaann fflluuiidd iiss aa fflluuiidd wwhhoossee ffllooww
pprrooppeerrttiieess aarree nnoott ddeessccrriibbeedd bbyy aa ssiinnggllee ccoonnssttaanntt
vvaalluuee ooff vviissccoossiittyy..
Many polymer solutions and molten polymers are
non-Newtonian fluids, as are many commonly found
substances such as ketchup, starch suspensions,
paint, blood and shampoo.
IInn aa nnoonn--NNeewwttoonniiaann fflluuiidd,, tthhee rreellaattiioonn bbeettwweeeenn tthhee
sshheeaarr ssttrreessss aanndd tthhee ssttrraaiinn rraattee iiss nnoonnlliinneeaarr,, aanndd
ccaann eevveenn bbee ttiimmee--ddeeppeennddeenntt.. TThheerreeffoorree aa ccoonnssttaanntt
ccooeeffffiicciieenntt ooff vviissccoossiittyy ccaannnnoott bbee ddeeffiinneedd..

9. TYPES OF NON
NEWTONIAN FLUIDS
1. Bingham plastics.
They have linear shear stress and strain relationship which
require a finite yield stress before they begin to flow, i.e., the
shear stress-strain curve doesn’t pass through origin.
Eg- clay suspensions, drilling mud, toothpaste, mayonnaise,
chocolate, and mustard. The classic case is ketchup which will
not come out of the bottle until you stress it by shaking.

10. 2. Pseudoplastic Flow
Polymers in solutions such as tragacant, sodium
alginate, methylcellulose
Viscosity decreases with an increase in shear
thinning
Caused by the re-alignment of polymer and/or the
release of solvents associated with the polymers
3. Dilatant Flow
Volume increases when sheared
Shear thickening
Suspension containing high-concentration of small
deflocculated particles

11. THE RELATIONSHIP OF
SHEAR STRESS-STAIN FOR
ALL FLUIDS:

12. There are also fluids whose strain rate is a function of
time. Fluids that require a gradually increasing shear
stress to maintain a constant strain rate are referred to
as rheopectic.
An opposite case of this, is a fluid that thins out with
time and requires a decreasing stress to maintain a
constant strain rate (thixotropic).

13. THIXOTROPY
is the property of some non-Newtonian
pseudoplastic fluids to show a time-dependent
change in viscosity; the longer the fluid
undergoes shear stress, the lower its viscosity.
A thixotropic fluid is a fluid which takes a
finite time to attain equilibrium viscosity when
introduced to a step change in shear rate.
the term is sometimes applied to pseudoplastic
fluids without a viscosity/time component.
Many gels and colloids are thixotropic
materials, exhibiting a stable form at rest but
becoming fluid when agitated.

14. THANK
YOU!