COLLOIDAL STATES

1. The Colloidal State

2. CONTENTS
• WHAT ARE COLLOIDS?
• LYOPHOBIC AND LYOPHILIC COLLOIDS?
• PREPERATION OF COLLOIDAL SOLUTION
• PURIFICATION OF COLLOIDAL SOLUION
• GENERAL PROPERTIES OF COLLOIDAL SYSTEM
• ELECTRIC DOUBLE LAYER

3. WHAT ARE COLLOIDS?
• A homogeneous non-crystalline substance
consisting of large molecules or
ultramicroscopic particles of one substance
dispersed through a second substance.
Colloids include gels, sols, and emulsions; the
particles do not settle, and cannot be
separated out by ordinary filtering or
centrifuging like those in a suspension.

7. LYOPHOBIC AND
LYOPHILIC
COLLOIDS?

11. LYOPHOBIC AND LYOPHILIC COLLOIDS?

12. PREPERATION
OF
COLLOIDAL SOLUTION

13. PREPARATION OF LYOPHILIC COLLOIDS
• Lyophilic colloids are colloids where the
particles have a strong affinity for the liquid it
is dispersed in. This makes these types
of colloids very stable and easy to prepare.
Typically they can be prepared simply by
mixing the particles with the liquid, sometime
with the addition of heat.

14. PREPARATION OF LYOPHOBIC COLLOIDS
• Lyophobic colloids cannot be prepared just by
heating, they need to be prepared by some
special methods.
• The two methods by which the lyophobic
colloids can be prepared are as follows:
1)Dispersion method
2)Condesation method

15. 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’sparticles into small in size.

16. 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:

17. 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.

18. I . Mechani cal Di sper si on
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
dispersing medium.
 Examples :Making of sulphur sol with the use
of glucose as diluents.

19. I . Mechanical Dispersion
Method
 The diagram shows the mechanical
dispersion method.

20. I I . Electrical Dispersion
Method
 Alsoknown 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 itis dispersed into water
to form a metallicsol.

21. I I . Electrical Dispersion
Method
 Inthismethod,anelectricareisstruckbetween the
twoelectrodesofthemetal(whosecolloidal
solution is to be prepared)immersed in the
dispersion medium (saywater).
 Thedispersionmediumiscooledbysurrounding it
with a freezing mixture.High temperature of the
arcvaporizessomeofthemetal.Thevapour
condenses to the particlesof colloidal size on
cooling. The colloidal particlesthus formed get
dispersed in the medium to form a sol.of the
metal.

22. I I . Electrical Dispersion
Method
 This method is used for the preparation of
sols metals such as gold, silver, platinum etc.
Electtrical DispersionMethod

23. I I I . Peptization Dispersion
 The process of converting aprecipitateinto a
colloidalsol by shaking it with thedispersion
medium, in thepresence of a small amountof
electrolyte
 Electrolyte= Peptizing agent
 This method is used to convert a freshly
prepared precipitate into a colloidal sol

24. I I I . 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
peptizing agent.

25. 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 dispersing agent.
 For example, sediment ofAl(OH)3 willchange
into a colloid by adding a solution of AlCl3 ;
NiS will charge into sol when it is added into
H2S; and sediment ofAgCl willcharge into a
colloid by adding a solution of ammonia.

26. 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
creamso that the milk or creamform a stable
colloid. In this process, skim milk powder is
often used and it is conducted in a
homogenization device.

27. Summary of Dispersion Method
 Dispersion method - larger particles of a substance
(suspensions) are broken into smaller particles. The
following methods are employed.
 Thereare4 ways using dispersion method :
1. Mechanical Dispersion Method - thesubstance is
firstground 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
theaddition of suitableelectrolyte
4. Homogenization - is any of several processes used
to make a chemicalmixture the same throughout.

29. CONDENSATION METHOD
In this method, small particles are aggregated to form colloidal size particles.
Double Decomposition:
Example: Arsenious oxide is mixed with hydrogen sulfide to form arsenic
sulfide sol. The excess amount of hydrogen sulfide is removed by passing
stream of hydrogen.
As2O3 + 3H2S → As2S3 (sol) + 3H2O
Reduction:
Example: Noble gases are reacted with organic reducing agents like ethanol,
tannic acid, formaldehyde to form their respective sol.
AgNO3 + tannic acid → Ag-sol
Oxidation:
When hydrogen sulfide is passed through a solution of sulfur dioxide it forms
a sulfur sol.
2 H2S + SO2 → 2H2O + S

30. PURIFICATION OF COLLOIDAL DISPERSION:
1. Dialysis
2. Electrodialysis
3. Ultrafiltration
a) Colloidal dispersions + electrolytes  Stable
colloids
b) Stable colloids have dispersed particles,
electrolytes, dispersion medium.
c) Purification is separation of dispersed particles
only.

31. 1.Dialysis:
Semi permeable membrane has fine
pore. Ions/small molecules – pass
Colloidal particles (large)- retained.
 Solution inside membrane –
dialyser
 Solution outside membrane –
diffusate

32. 2. Electrodialysis:
 This is similar to diffusion but
enhanced by applying potential
difference.
 Non-ionic impurities can not be
separated.

33. 3. Ultrafiltration:
 Ordinary filter paper has large pore size – not
useful
 Ordinary filter paper impregnated with collodion
has small pores – separate colloid particles.

34. PROPERTIES OF COLLOIDS:
1.Optical properties
2.Kinetic properties
3.Electrical properties

35. 1. Optical properties:
Useful to measure size, shape, structure & molecular
weight of colloids. Includes light scattering &
turbidity.
Light scattering:
Mechanism:
Light + dispersed particle  polarize
dipoles  Emmitt light in all directions  light
scattering

36. Tyndall effect:
Light scattering is clearly visible in dark back
ground at perpendicular angle.
Light scattering studied in light, ultra, electron
microscopes.
1. Light microscope:
 Source of radiation – visible light
 2 separate particles are visible if distance
between them is 0.2µ.
 Not suitable for colloidal particles.

37. 2. Ultra microscope (dark-field microscope):
 Used to observe tyndall effect,
 Dispersed particles appear as bright spots in dark
back ground.
 Used to determine zeta potential.

38. 3. Electron microscope:
 Used to measure particle size, shape, structure
.
 Radiation source – high energy electrons (λ=
0.1A0)
 As wave length decreases resolution
increases.
 Particle photographs can be taken.

39. 2. Kinetic properties:
 Used to detect stability of system, molecular
weight of particles, transport kinetics.
 Includes Brownian motion, diffusion,
sedimentation, viscosity, colligative properties.
Brownian motion:
 Robert brown theory states colloidal particles (5µm)
continuous random motion b/o thermal energy.
 In motion they collide with walls, other particles and
change their direction, velocity. (light microscope)
 Particles move against gravitational force.
 Brownian motion stops with increase in size & viscosity.

40. Diffusion :
Colloidal particles of small size pass through the porous plug b/o brownian
motion.
Sedimentation:
 This is influenced by gravitational force, applicable for particle size
> 0.5 µm.
 Stokes law equation – velocity of sedimentation.
 Colloidal particles have brownian motion No sedimentation
 Forced sedimentation – ultra centrifuge.
Colligative properties:
Only osmotic pressure is suitable for measurement of molecular
weight of dispersed particles.

41. Sedimentation:
 This is influenced by gravitational force,
applicable for particle size > 0.5 µm.
 Stokes law equation – velocity of sedimentation.
 Colloidal particles have brownian motion No
sedimentatio
n
 Forced sedimentation – ultra centrifuge.
Applications:
1. Molecular weight estimation
2. Study micellar properties of drug.
Colligative properties:
Only osmotic pressure is suitable for
measurement of molecular weight of
dispersed particles.

42. ELECTRIC DOUBLE LAYER
• Electrical double layer is the structure of charge accumulation and
charge separation that always occurs at the interface when an
electrode is immersed into an electrolyte solution. The excess
charge on the electrode surface is compensated by an accumulation
of excess ions of the opposite charge in the solution.
• The electrical double layer (EDL) is the result of the variation
of electric potential near a surface, and has a significant influence
on the behaviour of colloids and other surfaces in contact
with solutions or solid-state fast ion conductors.
• The primary difference between a double layer on an electrode and
one on an interface is the mechanisms of surface charge formation.
With an electrode, it is possible to regulate the surface charge by
applying an external electric potential. This application, however, is
impossible in colloidal and porous double layers, because for
colloidal particles, one does not have access to the interior of the
particle to apply a potential difference.