Colloids: A Comprehensive Overview -Lecture 1

LastBenchPharmacist.blogspot.com
Learning Objectives
• At the end of this lecture, student will be able to
 Classify colloids with examples
 Compare different forms of colloidal sols
LastBenchPharmacist.blogspot.com 1
Faculty of Pharmacy © Ramaiah University of Applied Sciences
 Explain the types of colloids
L
a
s
t
B
e
n
c
h
P
h
a
r
m
a
c
i
s
t
.
b
l
o
g
s
p
o
t
.
c
o
m

Dispersed Systems
• What are dispersed systems?
• Main components of a dispersed system?
• Examples of dispersed system
Dispersed systems consist of particulate matter, known as the
dispersed phase, distributed throughout a continuous or dispersion
medium.
L
a
s
t
B
e
n
c
h
P
h
a
r
m
a
c
i
s
t
.
b
l
o
g
s
p
o
t
.
c
o
m

Dispersed System
L
a
s
t
B
e
n
c
h
P
h
a
r
m
a
c
i
s
t
.
b
l
o
g
s
p
o
t
.
c
o
m

Types of Dispersed Systems
L
a
s
t
B
e
n
c
h
P
h
a
r
m
a
c
i
s
t
.
b
l
o
g
s
p
o
t
.
c
o
m

Types of Dispersed Systems
Based on the size of dispersed particles
Molecular dispersion Coarse dispersion
Colloidal dispersion
5
L
a
s
t
B
e
n
c
h
P
h
a
r
m
a
c
i
s
t
.
b
l
o
g
s
p
o
t
.
c
o
m

Comparison of Dispersed Systems
CLASS
PARTICLE
SIZE
CHARACTERISTIC OF SYSTEM EXAMPLES
Molecular
dispersion
Less
than1
nm
Invisible in electron microscope
Pass through ultrafilter and semipermeable
membrane
Undergo rapid diffusion
Oxygen molecules,
ordinary ions,
glucose
Colloidal
dispersion
From 1
nm to
Not resolved by ordinary microscope
(although may be detected under
Colloidal silver sols,
natural and synthetic
dispersion nm to
0.5 μm
(although may be detected under
ultramicroscope)
Visible in electron microscope
Pass through filter paper
Do not pass semipermeable membrane
Diffuse very slowly
natural and synthetic
polymers, cheese,
butter, jelly, paint,
milk, shaving cream,
etc.
Coarse
dispersion
Greater
than 0.5
μm
Visible under microscope
Do not pass through normal filter paper
Do not dialyze through semipermeable
membrane
Do not diffuse
Grains of sand,most
pharmaceutical
emulsions and
suspensions, red
blood cells
L
a
s
t
B
e
n
c
h
P
h
a
r
m
a
c
i
s
t
.
b
l
o
g
s
p
o
t
.
c
o
m

Components of a Colloidal System
Solid Liquid Gas
Solid Liquid Gas
7
L
a
s
t
B
e
n
c
h
P
h
a
r
m
a
c
i
s
t
.
b
l
o
g
s
p
o
t
.
c
o
m

© Ramaiah University of Applied SciencesFaculty ofPharmacy
10
8
©M. S. Ramaiah University of Applied Sciences
L
a
s
t
B
e
n
c
h
P
h
a
r
m
a
c
i
s
t
.
b
l
o
g
s
p
o
t
.
c
o
m

10
9
L
a
s
t
B
e
n
c
h
P
h
a
r
m
a
c
i
s
t
.
b
l
o
g
s
p
o
t
.
c
o
m

10
10
L
a
s
t
B
e
n
c
h
P
h
a
r
m
a
c
i
s
t
.
b
l
o
g
s
p
o
t
.
c
o
m

10
11
L
a
s
t
B
e
n
c
h
P
h
a
r
m
a
c
i
s
t
.
b
l
o
g
s
p
o
t
.
c
o
m

Shapes of colloids
a) Spheres and globules
b) Short rods and prolate ellipsoids
c) Oblate ellipsoids and flakes
d) Long rods and threads
e) Loosely coiled threads
f) Branched threads
12
L
a
s
t
B
e
n
c
h
P
h
a
r
m
a
c
i
s
t
.
b
l
o
g
s
p
o
t
.
c
o
m

Surface area of colloids and its significance
A cube having a 1-cm edge and a volume
of 1 cm3 has a total surface area of 6 cm2
If the same cube is subdivided into smaller
cubes each having an edge of 100 μm, the
total volume remains the same, but the total
surface area increases to 600,000 cm2
L
a
s
t
B
e
n
c
h
P
h
a
r
m
a
c
i
s
t
.
b
l
o
g
s
p
o
t
.
c
o
m

Significance of large surface area in colloids
The possession of a large specific surface results in many of the unique
properties of colloidal dispersions
platinum is effective as a catalyst only when in the colloidal form
as platinum black
as platinum black
• This is because catalysts act by adsorbing the reactants onto their
surface. Hence, their catalytic activity is related to their specific
surface
L
a
s
t
B
e
n
c
h
P
h
a
r
m
a
c
i
s
t
.
b
l
o
g
s
p
o
t
.
c
o
m

Types of Colloidal Systems
Lyophilic colloids
• Systems containing
colloidal particles that
interact to an
appreciable extent
Lyophobic colloids
• Composed of
materials that
have little
attraction, if any,
Association colloids
• Aggregation of
amphiphilic
molecules to form
micelles
appreciable extent
with the dispersion
medium are referred
to as lyophilic
(solvent-loving)
colloids
for the dispersion
medium
• Lyophobic
(solvent-hating)
colloids
micelles
• The concentration
of monomer at
which micelles
form is termed the
CMC
15
L
a
s
t
B
e
n
c
h
P
h
a
r
m
a
c
i
s
t
.
b
l
o
g
s
p
o
t
.
c
o
m

Lyophilic colloids
• Systems containing colloidal particles that interact to an
appreciable extent with the dispersion medium arereferred
L
•
to as lyophilic (solvent-loving) colloids
16
•
L
a
s
t
B
e
n
c
h
P
h
a
r
m
a
c
i
s
t
.
b
l
o
g
s
p
o
t
.
c
o
m

ds
ning
les
an
tent
Lyophobic colloids
• Composed of materials that have little
attraction, if any, for the dispersion medium
tent
rsion
ferred
)
17
• Lyophobic (solvent-hating) colloids
L
a
s
t
B
e
n
c
h
P
h
a
r
m
a
c
i
s
t
.
b
l
o
g
s
p
o
t
.
c
o
m

bic colloids
osed of
rials that
little
tion, if any,
Association colloids
• Aggregation of amphiphilic molecules to form
micelles
Faculty of Pharmacy
tion, if any,
e
rsion
um
obic
nt-hating)
18
© Ramaiah University of Applied Sciences
• The concentration of monomer atwhich
micelles form is termed the CMC
L
a
s
t
B
e
n
c
h
P
h
a
r
m
a
c
i
s
t
.
b
l
o
g
s
p
o
t
.
c
o
m

Lyophilic colloids
• Lyophilic colloidal sols are usually obtained simplyby
dissolving the material in the solvent being used
• Example, the dissolution of acacia or gelatin in water
• The attraction between the dispersed phase and the
• The attraction between the dispersed phase and the
dispersion medium, which leads to solvation, the attachment
of solvent molecules to the molecules of the dispersed phase
• In the case of hydrophilic colloids, in which water is the
dispersion medium, this is termedhydration
L
a
s
t
B
e
n
c
h
P
h
a
r
m
a
c
i
s
t
.
b
l
o
g
s
p
o
t
.
c
o
m

Types of lyophilic colloids
• Lyophilic colloids in aqueous
dispersion media
• Example; Gelatin and acacia in
aqueous dispersion media
Hydrophilic
sols
• Lyophilic colloids in
nonaqueous, organic solvents
• Example: Rubber and
polystyrene in organic solvents
Lipophilic
colloids
20
L
a
s
t
B
e
n
c
h
P
h
a
r
m
a
c
i
s
t
.
b
l
o
g
s
p
o
t
.
c
o
m

Preparation of Lyophilic colloids
• The dispersed phase is directly added to dispersion mediumin
cold or by warming
• Colloidal solutions of starch, gelatin, etc, in water can be
prepared by this method
prepared by this method
L
a
s
t
B
e
n
c
h
P
h
a
r
m
a
c
i
s
t
.
b
l
o
g
s
p
o
t
.
c
o
m

Lyophobic Colloids
• Absence of a solvent sheath around the particle
• Generally composed of inorganic particles dispersed in water
• Examples of such materials are gold, silver, sulfur, arsenous
sulfide, and silver iodide
Finest gold sol is red in colour; as the size
of particles increases, it appears purple,
then blue and finally golden
L
a
s
t
B
e
n
c
h
P
h
a
r
m
a
c
i
s
t
.
b
l
o
g
s
p
o
t
.
c
o
m

Preparation of Lyophobic colloids
• Dispersion
• Condensation
– Chemical Methods
– Exchange solventmethod
– Change of physical state
L
a
s
t
B
e
n
c
h
P
h
a
r
m
a
c
i
s
t
.
b
l
o
g
s
p
o
t
.
c
o
m

Lyophobic Colloids
Methods to prepare lyophobic colloids
a) Dispersion methods, in which coarse particles are reduced in
size
 Mechanical dispersion
 Mechanical dispersion
 Electric dispersion or Bredig’s Arc Method
 Peptization or chemical dispersion
 Ultrasonic dispersion
L
a
s
t
B
e
n
c
h
P
h
a
r
m
a
c
i
s
t
.
b
l
o
g
s
p
o
t
.
c
o
m

Dispersion methods
• Use of high-intensity ultrasonic generators operatingat
frequencies in excess of 20,000 cycles per second
• Colloid mills - in which the material is sheared between two
rapidly rotating plates set close together, reduce only a small
amount of the total particles to the colloidal sizerange
L
a
s
t
B
e
n
c
h
P
h
a
r
m
a
c
i
s
t
.
b
l
o
g
s
p
o
t
.
c
o
m

28
26
L
a
s
t
B
e
n
c
h
P
h
a
r
m
a
c
i
s
t
.
b
l
o
g
s
p
o
t
.
c
o
m

Colloid Mill
Colloid mill works on the rotor-stator principle. The equipment breaks
down materials by forming dispersion of materials in a liquid.Shearing
takes place in a narrow gap between a static cone (the stator) and a
rapidly rotating cone (the rotor).
27
L
a
s
t
B
e
n
c
h
P
h
a
r
m
a
c
i
s
t
.
b
l
o
g
s
p
o
t
.
c
o
m

Bredig’s Arc Method
Production of an electric arc
within a liquid. Owing to the
intense heat generated by the
arc, some of the metal of the
arc, some of the metal of the
electrodes is dispersed as vapor,
which condenses to form
colloidal particles
28
L
a
s
t
B
e
n
c
h
P
h
a
r
m
a
c
i
s
t
.
b
l
o
g
s
p
o
t
.
c
o
m

Peptization or Chemical Dispersion
• Redispersion of freshly prepared precipitate into the sol by
adding an electrolyte containing common ion is called
peptization electrolyte used is called peptizing agent
• The peptization action is due to the preferential adsorptionof
one of the ions of the electrolyte on the precipitate
• Example:
29
L
a
s
t
B
e
n
c
h
P
h
a
r
m
a
c
i
s
t
.
b
l
o
g
s
p
o
t
.
c
o
m

Ultrasonic Dispersion
• Use of high intensity ultrasonicwaves
• These high energy waves propagate through dispersion
medium
• Result in alternating high pressure and low pressurecycles
• This mechanical stress causes ultrasonic cavitation and high
speed liquid jets in liquids.
• This results in breakdown of bigger particles into colloidal
range particles
• Example : oils, mercury, sulphides, metal oxides
L
a
s
t
B
e
n
c
h
P
h
a
r
m
a
c
i
s
t
.
b
l
o
g
s
p
o
t
.
c
o
m

Condensation Methods
L
a
s
t
B
e
n
c
h
P
h
a
r
m
a
c
i
s
t
.
b
l
o
g
s
p
o
t
.
c
o
m

 Materials of subcolloidal dimensions are caused to aggregate
into particles within the colloidal size range
 These methods involve chemical reactions such as reduction,
 These methods involve chemical reactions such as reduction,
oxidation, hydrolysis and double decomposition
L
a
s
t
B
e
n
c
h
P
h
a
r
m
a
c
i
s
t
.
b
l
o
g
s
p
o
t
.
c
o
m

• Involve chemical reactions
• Need to maintain factors like temperature, pressure,
concentration, etc.
• Final purification for removal of unwanted ions shouldbe
done by dialysis
L
a
s
t
B
e
n
c
h
P
h
a
r
m
a
c
i
s
t
.
b
l
o
g
s
p
o
t
.
c
o
m

Oxidation Methods
Preparation of colloidal sulphur
• When aqueous solution of H2S is exposed to air, it slowly gets
oxidises to sulphur. The sulphur so formed remains in water in
the colloidal state.
the colloidal state.
34
L
a
s
t
B
e
n
c
h
P
h
a
r
m
a
c
i
s
t
.
b
l
o
g
s
p
o
t
.
c
o
m

Reduction Method
Preparation of Gold Sol:
• Metals like silver, gold, platinum, mercury, lead, can be
obtained in the colloidal state by the reduction of their salt
solutions (dilute) using suitable reducing agents like hydrogen
sulphide, formaldehyde, stannous chloride, tannic acid,etc.
35
L
a
s
t
B
e
n
c
h
P
h
a
r
m
a
c
i
s
t
.
b
l
o
g
s
p
o
t
.
c
o
m

Hydrolysis Method
Preparation of Ferric Hydroxide Sol
• Colloidal solution of ferric hydroxide is obtained by boilinga
dilute solution of ferric chloride
L
a
s
t
B
e
n
c
h
P
h
a
r
m
a
c
i
s
t
.
b
l
o
g
s
p
o
t
.
c
o
m

Exchange Solvent Method
• Involves taking a solution of the substance in one solventand
pouring it into another solvent in which the substance is
relatively less soluble
• Example: Preparation of sulphur or PhosphorousSol
L
a
s
t
B
e
n
c
h
P
h
a
r
m
a
c
i
s
t
.
b
l
o
g
s
p
o
t
.
c
o
m

Change of Physical State
• Colloidal solution of certain elements such as mercury and
sulphur are obtained by passing their vapours through cold
water containing a stabilizer (an ammonium salt orcitrate)
L
a
s
t
B
e
n
c
h
P
h
a
r
m
a
c
i
s
t
.
b
l
o
g
s
p
o
t
.
c
o
m

Summary
•
•
•
Colloidal dispersion - From 1 nm to 0.5 μm
Not resolved by ordinary microscope (although may be
detected under
ultramicroscope) Visible in electron microscope Pass through
filter paper Do not pass semipermeable membrane Diffuse
•
filter paper Do not pass semipermeable membrane Diffuse
very slowly
Examples - Colloidal silver sols, natural and synthetic
polymers, cheese, butter, jelly, paint, milk, shaving cream, etc.
• Types – Lyophillic, lyophobic and association colloids
• Preparation of lyophobic colloids - dispersion methodsand
condensation methods
L
a
s
t
B
e
n
c
h
P
h
a
r
m
a
c
i
s
t
.
b
l
o
g
s
p
o
t
.
c
o
m

Colloids: A Comprehensive Overview -Lecture 1

More Related Content

Similar to Colloids: A Comprehensive Overview -Lecture 1

More from NEHA GUPTA

Recently uploaded

Colloids: A Comprehensive Overview -Lecture 1