rheology_handout.pdf
TRANSCRIPT
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1Pavan Muttil, Ph.D.PHRM 701 Pharmaceutics IFall 2014
From rheo(toflow)andlogos(science) StudyofdeformationandflowpropertiesofmatterCanbeappliedtoallformsofmatter Primarilyfocusedonliquidsandsemisolidsinpharmaceuticalsciences
Usedtodescribetheconsistencyofdifferentproducts Viscosity measureofresistancetofloworthickness Elasticity stickinessorstructure
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2Rheologyofsemisolids
Newtonian
NonNewtonian
Plastic
Pseudoplastic
DilitantThixotropy
ShearStress Velocity(v)ofamaterialspreadoverasmalldistance(x)thatittravels(rateofshear)isproportionaltosheerstress applicationofhorizontalforce(F)overaunitarea(A)
Coefficientofviscosity() Parameterthatdefinestheresistancetoflow
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3Shearstress Unitsofforce/unitarea=dynes/cm2
Rateofshear Unitsofvelocity/unitsofdistance=(cm/s)/cmor1/secorsec1
Viscosity() (dynes/cm2)s dynes=g(cm/s2)
[g(cm/s2)]s/cm2 =g/cms poise cps(usedforlowviscosityliquids)1cps=(1/100)poise
Reciprocalofviscosity =1/Rheogram
Graphicrepresentationofrateofshearversussheerstress
Rat
e of
She
ar (s
-1)
Shear Stress (dynes/cm2)
Slope = fluidity
units for fluidity- cm s/g (reciprocal of poise)
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4Rate of Shear (s-1) 200 400 600 800 1000
Shear Stress (dynes/cm2)
50 100 150 200 250
ThefollowingdatashowtherateofshearasafunctionofshearstressforaNewtonianfluidat25C.Determinethefluidityandviscosityofthefluid.
Rate of Shear (s-1) 200 400 600 800 1000
Shear Stress (dynes/cm2)
50 100 150 200 250
Viscosity= 50/200 = 0.25
Fluidity = 1/0.25 = 4
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5 Viscosityisindependentofshearstress AlsoknowasAbsoluteViscosity Slopeisconstant
Commonlyhavelowmolecularweightsandmolecularhomogeneity Acetone,water,ethanol,oliveoil,glycerin
Viscositydecreasessharplywithincreasingtemperature
Viscositydecreasessharplywithincreasingtemperature
A = Constant (same units as viscosity)
Ev = Activation energy (cal/mol or kcal/mol)
R = Universal Gas Constant (1.987 cal/mol K)
T = Absolute temperature (C + 273)
ln
1/T (K-1)
Y-int = ln A
Slope = Ev/R
Y= b + mx
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6Theviscosityofhumanplasmaat37Cis1.2cps.AssumingtheplasmabehaveslikeaNewtonianfluid,determinetheviscosityofplasmarequiredforaninfusionthatiskeptatroomtemperature(25C). Theactivationenergyofplasmais4.25x103 cal/mole
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73types
Plasticrheology Pseudoplasticrheology Dilatant rheology
Observedincomplexheterogeneoussystems(Relationshipbetweenshearstressandrateofshearisnonlinear)
Describesasituationinwhichnoflowoccursinresponsetoshearstressuntilatransitionpointisreached Yieldvalue() Minimumshearstressrequiredbythesystembeforeitdeformsandbeginstoflow
Onceyieldvalueisreached,therelationshipbetweenshearstressandrateofshearbecomeslinear
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8Rat
e of
She
ar (s
-1)
Shear Stress (dynes/cm2)
Slope = fluidity
= yield value
BinghambodiesSeeningels,ointments,andcreamsImportanttodetermine offinalproduct Magnitudeofstressiscriticalforpatientuseofproduct Measurementofforcerequiredtospreadtheproductontheskin Toohighavaluewillnotalloweasyrubbing Toolowavaluewillresultinaproductthatruns
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9Rate of Shear (s-1) 250 500 750 1000 1500
Shear Stress (dynes/cm2)
162.5 275 387.5 500 725
The following data show the rate of shear as a function of shear stress for a topical formulation that exhibits plastic rheology. Determine the yield value and viscosity of the fluid.
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Observedinsystemsthatdeformandflowinstantaneouslywithappliedstress Relationshipisnotlinear
Rat
e of
She
ar (s
-1)
Shear Stress (dynes/cm2)
A
B
Shearthinningsystem viscosityatpointAishigherthanatpointB
Tears
Ketchup
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Increase shear stress
Decrease shear stress
Globular Form(higher viscosity)
Uncoiled Form(lower viscosity)
Rat
e of
She
ar
(s-1
)
Shear Stress (dynes/cm2)
A
B
Observedinsystemsthatdeformandflowinstantaneouslywithappliedstress Relationshipisnotlinear
Rat
e of
She
ar (s
-1)
Shear Stress (dynes/cm2)
A
B Shearthickeningsystem viscosityatpointAislowerthanatpointB
Whippingcream
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Thecomparativelyslowrecoveryofthematerialstructureonstandingthatwaslostbyshearthinning
TimerequiredfortherecoveryofpolymerconfigurationoncestresshasbeenREMOVED
Rat
e of
She
ar (s
-1)
Shear Stress (dynes/cm2)
A
B
D
C
DegreeofHysteresis maytakeashorterorlongertimetoreacquirestructureandbecomeviscousuponstanding
Suspensionandemulsions
SpreadingandAdherencetotheSkinRemovalfromjarsorextrusionfromtubesCapacityofsolidstomixwithmiscibleliquidsReleaseofdrug frombase