SUBMITTED BYMrs. Uzma Ali
• Definition• Viscosity• Newtonin fluid• Non-Newtonin fluid• Determination of flow properties• Application
• “ Rheology is concerned with the flow and deformation of materials experiencing an applied force.”
• “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 of viscosity is poise.
Coefficient of viscosity
• “ Ratio of applied stress and rate of shear”• If viscosity increase then shear stress increase:
Rate of shear
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
• Fluids which obey Newtonian equation is called Newtonian fluid.
• “ Force per unit area ”• S= F/A
• S= ᶯ du/dx
• ᶯ = S/du/dx
• ᶯ = F/A/du/dx
• This is Newtonian equation
• 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
Types of Non-Newtonian fuid
• “ 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.”
• A Bingham body does not begin to flow until a shearing stress, corresponding to the yield value exceeded.
• ᶯpl= S-fb
• “ 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.
The viscosity of the pseudoplastic materials
deceases with the increase in the rate of shear
S =K du/dx n=1n
• 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
• To change by touch• It is defined as a reversible transition from a gel to a
sol• Bentonite gel is good example
• 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.
• Transformation of dilute concentration into viscous concentration
• Occur due to gradual growth in molecular structures over the time
Determination of flow properties
1) Capillary viscometer: Ostwald U-tube viscometer Suspended level viscometer
2) Rational viscometer Concentric cylinder viscometer Cone plate 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
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
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
viscosity “The absolute viscosity
divided by the density
of a liquid at definite temperature.”
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
Concentric cylinder viscometer
• C =4ᴫ hὠᶯ • 1/ r1 – 1/r2
• C= Torsion constant• h= height of inner cylinder• ὠ = angular velocity• r1 & r2 = radius of outer and inner cylinder
• Shear rate not uniform throughout the process• Frictional drags increase in temperature• Cleaning difficult
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
• G= torque on cone
• R= radius of cone
• Ω= radial velocity of plate
• Ψ = angle between cone and plate
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
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
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.
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.