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, ..,
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:
, () ,
( )
, ( )
( )
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What is a dispersion at molecular level?
What makes them physically stable?
Interfacial Phenomena
Coarse dispersion 10 to 50 m Fine dispersion 0.5 to 10 m
Colloidal 1 nm to 0.5 m
What happens at interface is critical!!
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Suitable For Drugs with low solubility
Pharmaceutical suspensions are uniform dispersions ofsolid drug
particles in a vehicle in which the drug hasminimum solubility.
Colloidal suspension 1 nm to 0.5 m Coarse suspension 1 to 100 m
May be for oral, ophthalmic, parenteral, or topical use
Oral suspensions may be aqueous preparations withflavored,
sweetened vehicles or powder products fororal suspension
Marketed preparations: ready-to-use dry powders which must be
reconstituted before administration
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10
10
10
10
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flocculation or caking
determined by forces of attraction (van der Waals)versus forces
of repulsion (electrostatic)
deflocculated repulsion> attraction
affected by [electrolytes]
flocculated
attraction > repulsion
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Electric Double Layer
----
++++
+
-+
-
++
-
+- ++ -
+
tightly
bound
diffuse
electroneutral
--++ + - -- +
gegenion
Nernst potential
zeta potential
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Electrical Double LayerElectrical Double Layer
----
-
---+
+
+
+
Surface
()
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, , , . .
, .
12/19/2013 2013 12
.
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Resuspend easily upon shaking Settle slowly after shaking
H m n mix f r Ph i ll n
chemically stable during its shelf life
Sterile (parenteral, ocular)
Gets into syringe (parenteral, ocular)
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Controlled Flocculation
electrolytes most widely used
reduce zeta potential
decrease force of repulsion
change pH
bridge formation
polymers adsorb to particle surface
bridging
viscosity, thixotropy
protective colloid action
most effective
alcohol reduction in zeta potential
surfactants form adsorbed monolayers on
particle surface efficacy is dependent on charge,
concentration
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State Rate of settling Sedimentationvolume
Nature
Flocculated Fast High Porous, easy toredisperse
Deflocculated Slow Low Compact, difficultto redisperse
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The suspension shall form
loose networks of flocksthat settle rapidly, do notform cakes
and are easy toresus end.
flock
Settling and aggregationmay result in formation ofcakes
(suspension) that isdifficult to resuspend or
phase separation (emulsion) cake
Cake & Flock must be Controlled
by Zeta Potensial, Viscosity andParticle Size
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12/19/2013 2013 20
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: 181818182222
(((( )
: ( )
(: )
( )
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F = Vu /V0 ; ideally, F should be equal to 1.0
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: 181818182222
(((( )
,
, ,
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(
!
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)
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Determine the absolute viscosity of syrup using a ball of radius
of 0.2 cm.The density of the ball is 2.33g/cc and the density of
the syrup is 1.33 g/cc
at 250 C. The rate of falling is 4.35 cm/sec.
Determine the velocity of settling of sulfur in water. The
average particleradius is 5.5 m. The density of sulfur and water at
250 C. is 1.96 and. ., . . . .
If the height of the bottle is 10 cm how long will it take to
completelysettle?
Particle size determination:
From the previous example, calculate the average particle size
of sulfur.
What is the necessary viscosity to reduce the sedimentation rate
from0.0071 cm/sec to 0.00071 cm/sec?
