UNIT II RHEOLOGY PPT Physical Pharmaceutics II

Physical Pharmaceutics II

1. Presentation
on
RHEOLOGY
Presented By: Ms. SarikaS. Suryawanshi
M. Pharm Pharmaceutics
Associate Professor
AshokraoMane College of Pharmacy, Peth
Vadgaon

2. Introduction:
Rheo–toflow
logos–science
Resistancetoflowofliquid&deformationof
solid
Usedinsimpleliquids,ointments,cream,
pastes
Changeinflowbehaviorunderstress
condition
1.Manufacturingofdosageforms:mixing,
flowingthroughpipes,fillingintocontainers
II.HandlingofDrugsforadministration:pouring
fromthebottle,extrusionfromatubeora
passageoftheliquidtoasyringeneedle

3. Conceptofviscosity
Shearstress:Forceperunitareawhich
appliedtobringtheflow.
ShearStressF=F’/A
Rateofshear:changeinvelocity,dv
withinfinitechangeindistance,dr
RateofshearG=dv/dr
Higherviscosity,greaterforceperunit
arearequiredtoproducerateofshear.
F=nG
n=coefficientofviscosity
Centipoise,cp=0.01P
CGS:dy.sec/cm2

4. Factors:
IntrinsicFactors
1.Molecularweight:Highermolecular
weight,higherviscosity
2.Large&irregularshapeparticles
moreviscousthanregularshape
3.Intermolecularinteraction:stronger,
particlessticktoeachother
enhancesviscosity

5. ExtrinsicFactors
Pressure:enhancescohesiveforces
Additionofnonelectrolytes:increases
Polymers
Strongelectrolytes:Decreases,alkali
metal
Temperature:breakingofcohesive
forcesleadstodecreaseviscosity

6. Determinationofflowproperties
CapillaryViscometer
Fallingsphereviscometer
AtaSinglerateofshearonepointonthe
curve
Newtonianfluids
Cup&Bob
Cone&Plate
Rateofshearmanypointsonthecurve
Both

7. Ostwald Viscometer
n1 = ρ1t1/ρ2t2 X n2
ρ1-density ofunknown 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,
dextran40 injection

9. BasedonHoepplervicometer
Glasstubeplacedvertically
Constanttemperaturejacketforwater
circulationisarrangedaroundglasstube
Steel/glassballdropped&allowedtoreach
equilibriumwithtempofouterjacket
Inverttubewithjacket
Notetimetakenfortheballtofallbetweentwo
marks
Newtonianliquids
n1=t(Sb-Sf)B
Sb&Sf-specificgravityofball&fluid
0.5-200000poise
NLT30sec

11. Rotationalviscometer
Bobrotatory
No.ofrpm&torquerepresentsrateof
shear&shearingstressrsp.
Pseudoplasticsystem-
n=KvW/v
W-shearingstress
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(NewtonianLawofFlow)
LiquidobeysNewton’slaw
F=nG
Shearstress&rateofshearintheform
curvecalledrheogramorconsistencycurve
Rheogrampassesthroughorigin&slope
givesthecoefficientofviscosity
InaNewtonianfluid,therelationbetweenthe
shearstressandthestrainrateislinear
Eg:water,glycerin,solutionofsyrup

17. Non-Newtonian
DoesnotfallowsNewton'slaw
Manypolymersolutionsandketchup,
starchsuspensions,paint,bloodand
shampoo.
Plastic
Pseudoplastic
Dilatant

18. Plastic
Curvedoesn'tpassthroughtheorigin.
Substanceinitiallybehaveslikeanelasticbody&
failstoflowwhenlessamountofstressisapplied.
Furtherincreaseinshearstressleadstononlinear
portiongetlinear
LinearportionextrapolatedintersectstheXaxisat
thepointcalledyieldpoint
flocculatedparticlesinsuspensions,butter,pastes,
gel
Yieldvaluerepresentsstressrequiredtobreakthe
interparticlecontactsoparticlebehaveindividually.
Oncestressisincreaseswithrateofshear

19. MaterialshowsplasticflowcalledBingham
bodies
Slope=mobility&reciprocaliscalled
plasticflow
U=F-f/G
F=hearstress
F=yieldvalue
G=rateofshear

21. PseudoplasticFlow
Curvebeginsatorigin(nearlyzeroatlowershear
stress)
Stressincreasewithrateofshearbutitisnonlinear
Polymersinwatersuchastragacanth,sodium
alginate,methylcellulose

23. DilatantFlow
Enhancesresistanceofflowwithincreasingrateof
shear
Volumeincreases,socalleddilatant
Shearthickening
Stressisremovedsystemreturnstoinitialstate
Suspensioncontaininghigh-concentrationofsmall
deflocculatedparticles
Suspensionofstarch
Zincoxide30%inwater

24. Atrest,moleculesarecloselypacked,
minimumvoidspace,amountofvehicleis
sufficienttofillvoidspace.
Whenshearstressisappliedparticlesare
openorexpands/dilatants
Increasesvoidspace,insufficientfluid,
particlenotwetted,slowspastelike
consistancy
FN=nG
Nishigherthan1

26. THIXOTROPY

27. Hysteresisloop
Up&downcurvesofthixotropicsystem
Regionbetweencurvesfortheincreasing&
decreasingshearrateramps
TheareaofHysteresisisameasurementof
thixotropicbreakdown.
Shearingrateofplasticthixotropicmaterialis
increasedatconstantratefrompointa–bthen
decreasedatsamerateatpointe.
ConnectivitygivesformationofHysteresisloopabe
Staringfrompointaifsampleonapplicationof
sheartakentopointb&ifatthispointshearrateis
heldconstantforsometime,t1secthendepending
uponextentoftimeofshear

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
Highlystructuredmaterialsuchas
parenteralsolution(Procainepenicillin
gelforinjectionin2%cmcsolution),
buldgedcurvedevelopslikespur
Duetosharpstructuralbreakdown
whentakenintosyringeneedle
Complexstrexhibitshighyieldvalue
calledspurvalueinupcurve
Thisvaluerepresentssharppointof
structuralbreakdownatlowshearrate

32. Negativethixotropy
NegativethixotropyKnownasanti
thixotropywhichrepresentstime
dependantincreasingapparentviscosity
ratherthandecreaseonapplicationof
shearingstress.
Thisiscalledsoltogel
Atrestingconsistsoflargenumberof
individualparticlesandsmallsize
floccules
Whenthesystemisshearedthe
moleculesofdispersedphasecolloids
Increaseincollisionfrequencyofthese
moleculescauseIncreaseininterpartical

33. Atequilibriumstateverysmallnumberof
largeflocculesexiststhereforesystem
exhibitssolform.
Againwhensystemisatrestlargesize
flocculesbreakupandgraduallyreturns
tooriginalstateofsmallsizefloccules
andindividualparticles.
Itcontains1-10%ofsolid,dilatant
systemaredeflocculatedcontaining
morethan50%byvolumeofsolid.

34. Observedinmagnesiummagma
Itwasobservedthatwhenmagnesium
magmawasshearedwithalternatively
firstbyincreasingthendecreasing
shearrates,itcontinuouslyget
thickened.
Withcontinuationofcycletheextent
ofthickeningreducesgraduallythen
reachestoequilibriumState.

35. Rheopexy
Soltransformstoagelmorereadily
afterithasbeendeformedbygentle
shakingandregularrollingandrocking
movements.
Rheopexyisanalogoustorheopexyand
fluidsbehaviorcalledrheopectic
Itprovidesamildturbulencewhichhelps
thedispersedparticlestoget
themselvesinrandomalignmenttore-
establishgelstructure.
Usedinplasticandpseudoplastic
system
Magnesium magma

36. Measurementsofthixotropy
Thixotropicmeasurementsofplastic
andpseudoplasticsystemcanbe
achievedbyuseofhysteresisloop
formedduringthixotropicbreakdown
ofthesystem.
Degreeofthixotropyobtainedby..
1.Structuralbreakdownwithtimeat
constantrateofshear
2.Structuralbreakdownwithtimeat
twodifferentratesofshear

37. Importance
Desirablepropertyinemulsion,
suspension,cream,ointment,pastes,
parenteralsuspensionfordepottherapy.
Onstoragegelonshakingsol.sopoured
outeasily.
Helpfulinimprovingstabilityof
thixotropicpharmaceuticalsystem.
Greaterthixotropyhigherphysical
stability.
Speardabilityofcreamandointmentcan
becorrectedwiththixotropicproperty


38. Pouringoflotionsfromcontainer,shape
ofcreamincontainer,extrusionofpaste
fromtubeshowshighthixotropic
property.
T agents: bentonite,kaolin
microcrystallinecelluloseforviscosity
whichobstructsedimentationand
creaming.
Degreeofthixotropymaychangeover
periodtime.Soplasticviscosity,spur
valueyieldvalueareimportant
parameters.

39. Deformation of solid
Deformation change in size and shape of
object changing dimensions
Stress
Force per unit area that applies on 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.Compressivestress
Compressiveforceactingperunitareaofthe
body
Forcesappliedisoppositetoeachother
Compressthedimensions
3.Shearstress
Shearforceactingperunitareaofthebody
Duetothisbodydevelopssomeresistive
forcewhichisparalleltoeachsurfacebut
oppositetodirectionofforceapplied
2.Indirectstress
Duetotorqueproducedinthebody
3.combinedstress
Combinationofabovetwotypesofstress

41. Strain
Measure the amount of deformation
If bar has original length L and load is
applied on bar length of barwill 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
3. Shear strain: Produced by shear force

42. Elasticmodulus
Ratioofstress/strain
Theconstantofproportionalitydependson
theMaterialbeingdeformedandnatureof
thedeformation.
Determineamountofforcerequiredperunit
deformation.

43. Hooke'sLaw
Inanelasticmemberstressisdirectly
proportionaltostrainwithinelasticlimit
N/m2
Young'smodulususedtoidentifyhowmuch
theMaterialiselastic
ElasticlimitmaximumstressthatNanbe
appliedtothesubstancebeforeitdeforms
permanently.
Initialstrainstraincurveisstraightline.
Stressincreases,curveisnolongerstraight.

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 equationFrom 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
Linear relationship observed with plots remaining parellel
at the applied pressure increases

46. TypeB
Initialcurveregionfollowedbyastraightline.
Hardermaterialhavinghigheryieldpressure
Lactose
TypesC
Initialsteeplinearregionwhichbecome
superimposedandflattenedoutasappliedpressure
isincreased
Significance
Usedtocharacterizesinglematerialandalsofor
powder
TworegionsofplotItypeBmaterialrepresentsthe
initialrepackingstageandsubsequentdeformation
process
Crushingstrengthoftabletsiscorrelatedwithvalues
ofKofplot