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186
9.4.2.1.3 Ion Dissolution
Pharmaceutical Dosage Forms and Drug Delivery
] are dispersed, the dispersed particles
ions on the surface of
gI Ag I
+
+ ions are present in the solution. In
this case, therefore, the silver and iodide ions are referred to as potential- determining ions, since their
concentrations determine the electric potential at the particle surface.
9.4.2.2 Electrical Double Layer
counterions)
cations
an electric double layer made up of
electrical double- layer
theory
At a particular distance from the surface, the concentration of anions and cations is equal; that is,
as a whole
Figure 9.1
attached to the particle surface is called the stern
planes
stern plane)
shear plane
Debye– Huckel radius or length par-
ameter
concentration in the solution.
9.4.2.2.1 Nerst and Zeta Potentials
Electrothermodynamic or Nerst potential
Figure 9.1
shear plane
electrokinetic or zeta potential,
ζ
ζ
(shear plane) and the electroneutral region of the solution.
ζ ζ potential is
ζ
ζ
potential.
TAR
=+
Q
r
v
E
P XP
AA
=
0
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Colloidal Dispersions
9.4.2.2.2 DLVO Theory
187
of colloidal dispersed particles are electric repulsion (VRVA) and that these
V
(9.7)
9.4.2.3 Electrophoresis
opposite charge.
μ) of a molecule is a function of its net charge (Q
(radius, r
=
v) per unit electrical
E
=
(9.8)
9.4.3 Colligative Properties
number
9.4.3.1 Lowering of Vapor Pressure
Raoult’s
law
(9.9)
A
X
A
P
0
∆
bb
Km=
∆TKm
ff
=
T
n
v
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188
PA is the vapor pressure of the colloidal solution;
and
is the vapor pressure of the pure solvent.
A
Pharmaceutical Dosage Forms and Drug Delivery
is the mole fraction of solute in the solvent;
solute in that solvent.
9.4.3.2 Elevation of Boiling Point
Addition of a nonvolatile solute leads to the elevation of boiling point due to the nonvolatile solute dis-
(9.10)
Kb is the molal boiling point elevation constant; b is the elevation of boiling point; and m is
the molal amount of solute in solution.
K b for different
solvents is available in the literature.
9.4.3.3 Depression of Freezing Point
Kf
(9.11)
m
f
is the molal amount of solute in the solution.
Kf for different solvents is available in the literature.
9.4.3.4 Osmotic Pressure
osmosis, and the relative difference in
osmotic pressure, π
=
=
RT MRT (9.12)
R is the gas constant; TM is the difference in the molar concentra-
n, per unit volume of solution, v.
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Colloidal Dispersions
189
and the temperature, the higher the osmotic pressure.
9.4.4 Optical Properties
Tyndall effect
eter or nephelometer
9.5 Physical Stability of Colloids
1.
2.
3.
1.
2.
9.5.1 Stabilization of Hydrophilic Colloids
coacervate
coacervation
incompatibility. Coacervation need not involve the interaction of charged particles. Coacervation of gelatin
9.5.2 Stabilization of Hydrophobic Colloids
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190
Pharmaceutical Dosage Forms and Drug Delivery
ζ
ζ
Review Questions
9.1
A
B
C
D
E All of the above
F
9.2 Compounds that tend to accumulate at the interface and reduce surface or interfacial tension are
A Antifoaming agents
B Detergents
C
D Surfactants
E Interfacial agents
9.3
A
B
C
D
E
9.4
of amino acids as solutions for parenteral administration requires careful consideration of the iso-
i
ii Assign either of the 2 pK
iii Predict the structure of
9.6 -
the particles is not used for this purpose.
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Colloidal Dispersions
191
9.7
9.8
A
B
phenomena.
C
submicron particles. Suggest the principle behind this application.
D
9.9
A
B
C
D All of the above
E
FURTHER READINGS
Aulton M.E., (Ed.) (1988) Pharmaceutics: The Science of Dosage Form Design
Physicochemical Principles of Pharmacy
Press.
Modern
Pharmaceutics
(Eds.) Theory and Practice of Contemporary Pharmaceutics
APh’s Complete Review
for Pharmacy
Martin’s Physical Pharmacy and Pharmaceutical Sciences
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10
Surfactants and Micelles
On completion of this chapter, the students should be able to
1.
2.
3.
4.
10.1 Introduction
or interfaces and reduce surface or interfacial tension. Common interfaces of pharmaceutical relevance
surfactant at the interface results in changes in the nature of the interface and reduces interfacial tension
enables drug particles to be dispersed in a suspension.
emulsifying agents, solubilizing agents,
detergents, and wetting agents.
LEARNING OBJECTIVES
DOI: 10.1201/9781003389378-12
192
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Surfactants and Micelles
10.2 Surfactants
193
water- liking water-
hating amphipathy, and the molecules
amphipathic molecules or amphiphiles
10.2.1 Types of Surfactants
anioniccationic
nonionic
TABLE 10.1
Anionic surfactants
• Sodium stearate
• Sodium cholate
Cationic surfactants
Nonionic surfactants
Ampholytic (Zwitterionic) surfactants
• N
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194
Pharmaceutical Dosage Forms and Drug Delivery
Ka
ampholytic compounds.
10.2.1.1 Anionic Surfactants
, RSO
RSO
3
4
, or
+ 12SO4+
22O]nSO
6- SO
4
). Some of these surfactants,
3
such as SDS, also known as sodium lauryl sulfate (SLS) (Figure 10.1
during in vitro
cleaner and in medicated shampoos.
10.2.1.2 Cationic Surfactants
22
34+ )
Cationic surfactants are used in fabric softeners and hair conditioners. In addition, cationic surfactants
cetrimide (Figure 10.1
as for cleaning contaminated vessels. Benzalkonium chloride (Figure 10.1
FIGURE 10.1 Structures of some surfactants.
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Surfactants and Micelles
10.2.1.3 Nonionic Surfactants
22O)n
Spans and Tweens
(Spans), such as sorbitan monopalmitate (Figure 10.1
10.2.1.4 Ampholytic Surfactants
Ka
Ka,Ka.
Lecithin (Figure 10.1
used for parenteral emulsions.
10.2.2 Hydrophile– Lipophile Balance System
– -
and more lipophilic.
Figure 10.2
10.2.2.1 Type of Emulsion Formed
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