A colloid is a substance microscopically
dispersed throughout another substance.
The word colloid comes from a Greek word
kolla, which means glue thus colloidal
particles are glue like substances. These
particles pass through a filter paper but not
through a semipermeable membrane.
Colloids can be made settle by the process
3. The colloidal system consist of two phases:
A dispersed phase ( A discontinuous phase )
A dispersion medium ( A continuous phase )
The dispersed-phase particles have a diameter of
between approximately 1nm – 0.5um .
Such particles are normally invisible in an optical view,
though their presence can be confirmed with the use of
an ultramicroscope or an electron microscope.
4. Homogenous mixtures with a dispersed phase in
this size range may be called colloidal
aerosols, colloidal emulsions, colloidal
foams, colloidal dispersions, or hydrosols.
If the dispersed phase is solid and the dispersion
medium is liquid then it is called colloidal
suspension but if the dispersed phase and
dispersion medium both are in liquid state then it
is known as colloidal emulsion.
5. The dispersed-phase particles or droplets are
affected largely by the surface chemistry present in
Some colloids are translucent because of
the Tyndall effect, which is the scattering of
light by particles in the colloid.
Other colloids may be opaque or have a slight
Colloidal solutions (also called colloidal
suspensions) are the subject of interface and
This field of study was introduced in 1861
by Scottish scientist Thomas Graham.
6. . Examples of colloids are silver solutions, milk,
synthetic polymers and blood etc.
8. forces play an important role in the interaction of
1) EXCLUDED VOLUME REPULSION:
IN LIQUID THEORY STATE:
In liquid state theory, the 'excluded volume' of a molecule
is the volume that is inaccessible to other molecules in
the system as a result of the presence of the first
The excluded volume of a hard sphere is eight times its
volume—however, for a two-molecule system, this
volume is distributed among the two particles, giving the
conventional result of four times the volume.
9. 2) ELECTROSTATIC INTERACTION :
Colloidal particles often carry an electrical charge and
therefore attract or repel each other. The charges of
both the continuous and the dispersed phase, as well as
the mobility of the phases are factors affecting this
3) VAN DER WAALS FORCE : van der Waals
force (or van der Waals interaction), is the sum of the
attractive or repulsive forces between molecules other
than those due to covalent bonds, the hydrogen bonds,
or the electrostatic interaction of ions with one another
or with neutral molecules or charged molecules
10. 4) STERIC FORCES :
Steric effects arise from the fact that each
atom within a molecule occupies a certain
amount of space. If atoms are brought too
close together, there is an associated cost
in energy due to overlapping electron
clouds (Pauli or Born repulsion), and this
may affect the molecule's preferred shape
(conformation) and reactivity.
15. Classification of Colloids based
on Nature of Interaction
Between Dispersed Phase and
16. Lyophilic Colloids
• Lyophilic colloids are liquid loving colloids (Lyo means
solvent and philic means loving).
Ease of Preparation:
• As these colloids are liquid loving, their solutions are
easy to prepare and can be prepared directly by mixing
colloid with liquid.
• Lyophilic sols are relatively stable as strong forces of
interaction exist between colloidal particles and liquid.
If large quantity of liquid is added to
precipitations or the colloidal solution is
stirred properly lyophilic sols can regain
their original state.
This shows that lyophilic sols are also
reversible in nature.
18. Lyophobic Colloids
Lyophobic colloids are liquid hating colloids (Lyo means
solvent and phobic means hating).
Ease of Preparation:
As these colloids are water hating, their solutions are easy to
prepare and cannot be prepared directly by mixing colloid
with liquid. Special methods are employed to prepare
Lyophobic sols are less stable as weak forces of interaction
exist between colloidal particles and liquid.
Lyophobic colloids do not regain
their original state as coagulated
mass cannot be dispersed into
This shows that lyophobic solutions
are also irreversible in nature.
20. Association colloids
• These are the colloids which behave as normal strong
electrolytes at low concentrations but exhibit colloidal
properties at higher concentrations due to the formation of
• The aggregated particles thus formed are called micelles.
• The associated colloids are usually formed by surfactants
(surface active agents) like soaps and synthetic detergents.
• These agents form micelles when present in solution at a
concentration greater than critical micellar concentration
22. Dispersion Methods
• In dispersion methods, colloidal particles
are obtained by breaking large particles of a
substance in the presence of a dispersion
medium. Since the solsformed are
unstable, they are stabilized by adding
mechanical energy input.
• Dispersion method in the preparation of
colloids can be done by crushing the large
suspension’s particles into small in size.
23. Dispersion Method
• In these methods, the bigger particles of a
substances are broken down to form smaller
particles of colloidal dimensions thus obtained
are stabilized by the addition of certain
stabilizing agents. Some important dispersion
methods are as follows:
24. I. Mechanical Dispersion Method
• In this method, the dispersion of the coarse
material (whose colloidal solution is to be
prepared) is carried out in a machine called
• Colloid mill - It consists of two heavy steel discs
separated by a little gap. The gap may be
adjusted according to the particle size desired.
The two discs rotate at high speed (about 8000
revolutions per minute) in the opposite direction.
25. I. Mechanical Dispersion Method
• A suspension of the substance in water is
introduced into the mill. The coarse particles
present in the suspension are grinded to the
particles of colloidal dimensions and get
dispersed in water to form a sol. Finer
dispersion can be obtained by adding an inert
diluents which prevents the colloidal particles
to grow in size.
26. I. Mechanical Dispersion Method
• Mechanical dispersion is also called direct
dispersion. It is a method of making a colloid
by crushing or milling a given solid and the
powder produced is dispersed into a given
• Examples : Making of sulphur sol with the use
of glucose as diluents.
28. II. Electrical Dispersion Method
• Also known as “Bredig arch method “
• Is a method of preparing colloids, especially
metallic sols. In this method, two metallic
wires functioning as electrodes are immersed
into water, then on both ends of wires is given
a strong enough electric current to be
evaporated and then it is dispersed into water
to form a metallic sol.
29. II. Electrical Dispersion Method
• In this method, an electric are is struck between
the two electrodes of the metal (whose colloidal
solution is to be prepared) immersed in the
dispersion medium (say water).
• The dispersion medium is cooled by surrounding
it with a freezing mixture. High temperature of
the arc vaporizes some of the metal. The vapour
condenses to the particles of colloidal size on
cooling. The colloidal particles thus formed get
dispersed in the medium to form a sol. of the
30. II. Electrical Dispersion Method
• This method is used for the preparation of sols
metals such as gold, silver, platinum etc.
Electtrical Dispersion Method
31. III. Peptization Dispersion
• The process of converting aprecipitate into a
colloidalsol by shaking it with thedispersion
medium, in thepresence of a small amountof
• Electrolyte = Peptizing agent
• This method is used to convert a freshly
prepared precipitate into a colloidal sol
32. III. Peptization dispersion
• In this method, a freshly prepared precipitate
of the substance is made to pass into the
colloidal state by the addition of a suitable
electrolyte. The process of dispersing a freshly
prepared precipitate into colloidal form by
using a suitable electrolyte is called
peptization. The electrolyte added is called
33. III. Peptization Dispersion
• In peptization, the larger particles is dispersed
into smaller particles in a colloidal size by
adding a particular electrolyte which acts as a
• For example, sediment of Al(OH)3 will change
into a colloid by adding a solution of AlCl3 ;
NiS will charge into sol when it is added into
H2S; and sediment of AgCl will charge into a
colloid by adding a solution of ammonia.
34. IV. Homogenization
• Homogenization is a process for preparing
something to become homogeneous. In this
preparation, a particular emulsifier is usually
added to emulsify the fat particles in milk or
cream so that the milk or cream form a stable
colloid. In this process, skim milk powder is
often used and it is conducted in a
35. Summary of Dispersion Method
• Dispersion method - larger particles of a substance
(suspensions) are broken into smaller particles. The
following methods are employed.
• There are 4 ways using dispersion method :
1. Mechanical Dispersion Method - the substance is
first ground to coarse particles.
2. Electical Dispersion Method - is used to prepare
sols of platinum, silver, copper or gold.
3. Peptization Dispersion - The process of
converting a freshly prepared precipitate into
colloidal form by the addition of suitable
4. Homogenization - is any of several processes used
to make a chemical mixture the same throughout.
Colloidal System is
the heterogenous biphasic system
dispersed phase ranges within 1-10
angstrom to few micrometres in
differs from other heterogenous and
homogenous solutions in terms of the size
of dispersed phase.
40. APPLICATIONS OF COLLOIDS
Colloids play an important role in pharmacy,in
our daily life and in industries.
A few of the important applications of colloids
are listed below.
42. PHARMACEUTICAL APPLICATIONS
Colloidal system are used as therapeutic
agents in different areas.
Colloidal medicines being finely divided, are
more effective and are easily absorbed in
Penicillin and streptomycin .
• Argyrol and protargyrol
47. APPLICATIONS IN FOOD INDUSTRY:
Many of our foods are
colloidal in nature.
Milk is an emulsion of
butterfat in water
protected by a protein,
Salad dressing, gelatin
deserts, fruit jellies.
Ice cream & Bread.
49. NON-DRIP PAINTS:
All paints are colloidal
dispersions of solid pigments
in a liquid medium.
paints also contain long-
At rest, the chains of
molecules are coiled.
stress is applied with a paint
brush, the coiled molecules
This renders the paint ‘non-
54. OTHER APPLICATIONS
Clarification of Municipal water:
The municipal water contains colloidal
Alum which yield ions, Al3+ is added to water
to coagulate the negatively charged clay
Al3+ + 3H2O ---- Al(OH)3 + 3H+
Al(OH)3 + 4H2O + H+ ----- Al(OH)3(H2O)4
55. OTHER APPLICATIONS
Artificial Kidney machine:
The human kidneys purify the blood by
dialysis through natural membranes.
The toxic waste products such as urea and uric
acid pass through the membranes
colloidal-sized particles of blood proteins
(haemoglobin) are retained
• A knowledge of colloid chemistry is essential
to understand some of the various natural
phenomena around us.
• Colloids make up some of our modern
• Dialysis,life saving treatment.
62. 1. THERAPY:
• Colloidal material are used for a variety of
pharmaceutical application including therapeutic &
diagnostic agents, drug delivery system.
• Example: copper colloids ( anti cancer) & mercury
colloids ( anti syphilis).
63. 2.DRUG PREPARATION:
• Drug substances may also be prepared as
colloidal sized particles to improve
bioavailability or therapeutic activity
.Example: colloidal sulphur etc.
64. 3.TABLETS COATING:
• Colloidal dispersion of gelatin is used in coating over
tablets & granules which upon drying leaves uniformly
dry film over them & protect them from adverse
condition of the atmosphere.
• Most of the medicines are colloidal such as Calcium &
Gold are administered by injections to raise the vitality
of human system.
66. 5.FOOD ITEMS:
• Large numbers of food particles which we use
in our daily life are colloidal in nature.
• Example: Milk, butter, & ice cream etc
67. 6.NUCLEAR MEDICINES:
Colloidal dispersion containing radioactive
isotopes are being used as diagnostic &
therapeutic agents in nuclear medicines.
Example: Colloidal gold is made by reducing a
solution of AgCl either by treatment with
69. Study Questions
• Define the following terms:
[continuous phase , Homogenous mixtures , Heterogenous, etc]
• Respond to the following questions:
State and describe the types of inter-particle interactions in a pharmaceutical system
State and explain the characteristic classification of colloidal system based on physical components
State and describe different methods of colloidal preparations
• Group work discussional questions:
Describe the pros and cons of colloidal systems as drug carrier and delivery system
Describe the various pharmaceutical and therapeutical applications colloidal system can be used
Describe the mechanisms involved in colloidal drug carrier and delivery entities for therapeutical effects