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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_5320_Библиотеки_им_академика_М_И_Перельмана
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196
TABLE 10.2
Pharmaceutical Dosage Forms and Drug Delivery
Names of Surfactants HLB
Sorbitan laurate (Span 20) 8.6
Sorbitan palmitate (Span 40) 6.7
Sorbitan stearate (Span 60) 4.7
Sorbitan oleate (Span 80) 4.3
1.8
16.7
14.9
11.0
16.9
Sodium oleate 18.0
Potassium oleate 20.0
FIGURE 10.2
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Surfactants and Micelles
10.2.2.2 Required HLB of a Lipid
197
required HLB (or RHLBfor the
of
).
TABLE 10.3
Oil Phase W/ O Emulsion O/ W Emulsion
Acetophenone 14
Cottonseed oil
16
17
Oleic acid 16
Ricinoleic acid 17
Stearic acid
14
14
14
14
16
Carbon tetrachloride 14
Castor oil 8
14
12
8 12
Aromatic mineral oil 4
4
Mineral spirits 4
Petrolatum
9
Candelilla
Carnauba 12
4 10
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10.2.2.3 Required HLB of a Formulation
Pharmaceutical Dosage Forms and Drug Delivery
% In the
Oil- Phase Ingredient
Mineral oil 10
3
4
Formulation
% Contribution
to the Oil Phase
RHLB of the
Ingredient
RHLB Contribution
to the Formulation
10.2.2.4 Assigning a Hydrophile– Lipophile Balance Value to a Surfactant
22
10.2.2.5 Selection of Surfactant Combination for a Target Hydrophile– Lipophile
Balance Value
10.3 Micelles
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Surfactants and Micelles
199
CMC
micelles
Figure 10.3).
the inside.
10.3.1 Types of Micelles
assume cylindrical or lamellar structures (Figure 10.3
reverse micelles
Figure 10.3).
10.3.2 Micelles Versus Liposomes
Figure 10.3). Although both micelles and liposomes are formed
FIGURE 10.3 -
tion reaches the critical micelle concentration (CMC). Elongation of spherical micelles at high concentration leads to the
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200
10.3.3 Colloidal Properties of Micellar Solutions
Pharmaceutical Dosage Forms and Drug Delivery
particles), since micelles are association colloids; that is, the associated surfactant molecules are col-
CMC.
aggregation number of
escape
.
Surface tension: As illustrated in Figure 10.4
is increased, more and more surfactant molecules partition into the surface or interface, leading to a
Conductivity
a reduced number of free ions available for conductance. As a surfactant is added to the solution, some of
Figure 10.4
Solubility
TABLE 10.4
Surfactant
Name Molecular Formula CMC (mM)
Sodium octant sulfonate
Sodium decane sulfonate
Sodium dodecane sulfonate
n- C817- SO3
n- C1021SO3
n- C12SO3
n- C12OSO3
n- C10213)3Br
n- C123)3Br
n- C12293)3Br
n- C1222O)8
n- C1222O)12
28
40 40
9
8 62
63 36
14
3
0.13 132
0.14 78
Molecules/ Micelle
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Surfactants and Micelles
FIGURE 10.4
201
Osmotic pressure: Micelles, formed above the CMC, act as association colloids, leading to an increase
in the osmotic pressure of the colloidal solution.
Light- scattering intensity
of colloidal micelles that scatter light.
10.3.4 Factors Affecting Critical Micelle Concentration and Micellar Size
• Size and structure of hydrophobic group
surfactant in the micelle.
• Nature of hydrophilic group:-
• Nature of counterions + is
-
to the series Cl+ + + .
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202
Pharmaceutical Dosage Forms and Drug Delivery
• Addition of electrolytes:
• Effect of temperature
nonionic surfactants.
• Alcohol
10.3.5 Krafft Point
Kt
Gold Book (
T), or 1/ TKt, the surfac
10.3.6 Cloud Point
Cloud point is the temperature at which some surfactants begin to precipitate, and the solution becomes
-
tant precipitation and cloudiness of the solution. At elevated temperatures, the surfactant separates as a
10.3.7 Micellar Solubilization
solubilization, and the incorporated sub-
stance is referred to as the solubilizate
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Surfactants and Micelles
203
the micelles.
10.3.7.1 Factors Affecting the Extent of Solubilization
1. Nature of surfactants
from C1218
2. Nature of solubilizate (drug being solubilized
Unsaturated compounds
3. Effect of temperature
temperature (
4. Effect of pH
Ka
10.3.7.2 Pharmaceutical Applications
•
form clear solutions for use as disinfectants.
•
∆GRTK
s
∆∆ ∆GHTS
ss s
=−
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204
Pharmaceutical Dosage Forms and Drug Delivery
FIGURE 10.5
J. Pharm. Sci
•
•
10.3.7.3 Thermodynamics/ Spontaneity
Gscient, K
In=− (10.1)
R is the gas constant; T is the absolute temperature.
Hs)
Ss) as:
(10.2)
∆∆HTSRTK
−=−
H
RT
∆
∆∆ ∆GHTS
ss s
=− =−−
∆∆ ∆GHTS
ss s
cal/mol=− =−−=−
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Surfactants and Micelles
ss
In
Or,
K
=− ⋅+
1
s
constant
Ss/ R
Gs
Gs is negative, the
Gs
Example 1:HsSs
cal/mol (298 K)( cal/kmol)
2830 26 3.
Example 2:HsSs
cal/mol (298 K)( cal/kmol)
1700 21 2326.
Review Questions
10.1
A Emulsions
B Suspensions
C Colloidal dosage forms
D Creams
E All of the above
10.2
A An increase in surface tension
B A decrease in surface tension
C
D All of the above
10.3
A
B Potassium stearate
C
D
E All of the above
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