This document provides information about colloidal dispersions. It defines colloids as mixtures where one substance is dispersed as very small particles (1-1000 nm) throughout another substance. Colloids are classified based on properties of the dispersed and continuous phases. Key characteristics include particle size, shape, surface area, and charge. Colloids exhibit optical properties like Tyndall effect and kinetic properties such as Brownian motion and electrophoresis. The stability of colloids can be impacted by the addition of electrolytes or other charged particles/colloids.

1. Colloidal dispersion
Prepared by:
Akshata A Jain
M-pharm (Pharmaceutics)

2. COLLOIDS
● The term colloid has been derived form the 2-greek words i.e "kola" & "edios".
● Kolla means glue & eidos means like, so colloid means glue like.
● A colloid is a mixture in which one substance which has fine particles
(dispersed phase) mixed into another substance (dispersion medium).
● The particles of the colloids have a range from 1 to 1000 nm in diameter.
● The solution is called colloidal dispersion because the particles of solutions
do not mix or settle down.
● Example: gelatin,acacia & rubber.

3. Types of Colloids
● Colloids can be classified according to different
properties of the dispersed phase and medium.
● Firstly, based on the types of particles of the dispersed
phase, colloids can be classified as:
1. Multimolecular colloids
2. Macromolecular colloids
3. Associated colloids

4. Classification of DispersedSystems:
● Dispersed systems consist of particulate matter (dispersed phase),
distributed throughout a continuous phase (dispersion medium).
● They are classified according to the particle diameter of the dispersed
material.
1. Molecular dispersions (less than 1 nm)
● Particles invisible in electron microscope
● Pass through semipermeable membranes and filter paper
● Particles do not settle down on standing Undergo rapid diffusion.
● Eg. ordinary ions, glucose Dispersed Systems

5. 2. Colloidal dispersions (1 nm - 0.5 um) –
● Particles not resolved by ordinary microscope, can be detected
by electron microscope.
● Pass through filter paper but not pass through semipermeable
membrane.
● Particles made to settle by centrifugation
● Diffuse very slowly
● E.g. colloidal silver solutions, natural and synthetic polymers.

6. 3.Coarse dispersions (> 0.5 um)
● Particles are visible under ordinary microscope.
● Do not pass through filter paper or semipermeable membrane.
● Particles settle down under gravity -
● Do not diffuse
● E.g. emulsions, suspensions, red blood cells.

7. Characteristics of dispersed phase
1. Particle size:
● This influence colour of dispersion.
● The wavelength of light absorbed by particle is approximately related to
its radius.
● The larger the particle the shorter the wavelength of light transmitted.

8. 2. Particle shape:
● Depends on the preparation method and affinity of dispersion
medium .This influence colour of dispersion.
● Shapes- spherical, rods, flakes, threads, ellipsoidal.
● Gold particles- spherical (red), disc (blue).

9. 3. Surface area:
● Particle size small- large surface area
● Effective catalyst, enhance solubility.

10. 4.Surface charge:
● Positive (+)= gelatin, aluminum.
● Negative (-) = acacia, tragacanth.
● Particle interior neutral, surface charged.
● Surface charge leads to stability of colloids because of repulsions.
Acacia
Gelatin

11. CLASSIFICATION OF COLLOIDS
Based of physical state of dispersed
phase an dispersion medium.
Based of nature of interaction between
dispersed phase and dispersion medium.
Based on molecular size in the dispersed
phase.
Based on appearance of colloids.
Based on electric charge on dispersion
phase.

12. Dispersed
phase
Dispersion
medium
Name of colloidal solution Examples of the colloid
Gas Liquid Foam Soap, soda water
Gas Solid Solid foam Cake, Bread
Gas Gas Does not exist -
Liquid Liquid Emulsion Milk, cream, butter
Liquid Solid Gel Curd, cheese, jellies
Liquid Gas Aerosol Mist, fog, clouds
Solid Gas Solid aerosol Smoke, dust
Solid Liquid Sols or colloidal suspension Paints, inks
Solid Solid Solid sol (solid suspension) Alloys, coloured glass
1. Based of physical state of dispersed phase an dispersion medium

13. 2. Based on nature of interaction between dispersed phase and
dispersion medium

14. 1. Lyophilic Colloids
● Colloidal solution in which the dispersed phase has a great
affinity for the dispersion medium. They are also termed as
intrinsic colloids.
● Such substances have tendency to pass into colloidal
solution when brought in contact with dispersion medium.
● If the dispersion medium is water, they are called
hydrophilic or emulsoids.
● The lyophilic colloids are generally self- stabilized.
Reversible in nature and are heavily hydrated.
● Examples are starch, gelatin, rubber, protein etc.

15. 2. Lyophobic colloids
● Colloidal solutions in which the dispersed phase has no affinity to
the dispersion medium.
● These are also referred as extrinsic colloids.
● Such substances have no tendency to pass into colloidal solution
when brought in contact with dispersion medium.
● The lyophobic colloids are relatively unstable due to they are
irreversible by nature and are stabilized by adding small amount of
electrolyte.
● They are poorly hydrated.
● If the dispersion medium is water, the lyophobic colloids are called
hyrophobic or suspenoids.
● Examples: sols of metals like Au, Ag, sols of metal hyroxidase and
sols of metal sulphide.

16. 3. Associated colloids
● These colloids behave as normal electrolytes at low
concentrations but behave as colloids at higher concentrations.
● These associated colloids are also referred to as micelles.
● Sodium stearate behave as electrolyte in dilute solution but
colloid in higher concentrations.
● Examples: Soaps, higher alkyl , polythene oxide.

17. 3.Based on molecular size in the dispersed phase.
1. Multi molecular colloids
● Individual particles of the dispersed phase consists of
aggregates of atoms or small molecules having diameter less
than 10-7cm.
● The particles are held by weak vander waal's forces.
● Example; gold sol, sulphur sol.
2. Macro molecular colloids
● The particles of dispersed phase are sufficiently large in size
enough to be of colloidal solution.
● These are called Natural Polymers.
○ Examples are starch, cellulose and proteins.

18. 4.Based on appearance of colloids
1. SOLS
● When a colloidal solution appears as fluid.
● The sols are generally named as dispersion medium.
● When the dispersion medium is water, the sol is known as
hydrosol or aquosol.
● When the dispersion medium is alcohol or benzene it is called
alcosol and benzosol respectively.
2.GELS
● When a colloidal solution appear as solid.
● The rigidity of gel varies from substance to substance.
● Examples: jelly, butter, cheese, curd

19. 5. Based on electrical charge on dispersion phase
1. POSITIVE COLLOIDS
● When dispersed phase in a colloidal solution carries a positive charge.
● Examples: Metal hyroxides like Fe(OH)3, Al(OH)2, methylene blue sol
2. NEGATIVE COLLOIDS
● When dispersed phase in a colloidal solution carries a negative charge.
● Examples: Ag sol, Cu sol

20. Properties of colloids
• Physical Properties
• Optical Properties
• Kinetic Properties
• Electrical Properties

21. 1. Physical properties of colloids
Heterogeneity:
● Colloidal solutions consist of two phases-dispersed phase and
dispersion medium.
Visibility of dispersed particles:
● The dispersed particles present in them are not visible to the
naked eye and they appear homogenous.
Filterability:
● The colloidal particles pass through an ordinary filter paper.
However, they can be retained by animal membranes,
cellophane membrane and ultra filters.

22. Stability:
Lyophilic sols in general and lyophobic sols in the absence of
substantial concentrations of electrolytes are quite stable.
Colour:
The colour of a colloidal solution depends upon the size of colloidal
particles present in it.

23. 2.Optical properties of colloids
Tyndall Effect
● When an intense converging beam of light is passed through a
colloidal solution kept in dark, the path of the beam gets
illuminated with a bluish light.
● The Tyndall effect is due to the scattering of light by colloidal
particles.
● Tyndall effect is not exhibited by true solutions. This is because
the particles present in a true solution are too small to scatter
light.

24. Ultra Microscope
(Dark-field microscope)
● Used to observe tyndall effect
● Dispersed particles appear as bright spots in dark background
this capable of yielding pictures of actual particles size, shape
and structure of colloidal particles.
● Used to determine zeta potential.

25. Light scattering method
● depend on tyndall effect.
● used to give information about particle size and shape and for
determination of molecular weight of colloids.
● Used to study proteins, association colloids and lyophobic sols.
Scattering described in terms of turbidity.
● Turbidity: the fractional decrease in intensity due to scattering as the
incident light passes through 1 cm of solution.
● Turbidity is proportional to the molecular weight of lyophilic colloid
.Optical Properties of Colloids.
T: turbidity M: molecular weight
B: interaction constant He: constant for a particular system
C: conc of solute in gm/cc of solution
He/T=1/M+2Bc

26. 3. Kinetic properties of colloids
● used to detect stability of system, molecular weight of particles,
transport kinetics.
Brownian movement
● The continuous zigzag movement of the colloidal particles in the
dispersion medium in a colloidal solution is called Brownian
movement.
● Brownian movement is due to the unequal bombardments of the
moving molecules of dispersion medium on colloidal particles.
● The Brownian movement decreases with an increase in the size
of colloidal particle.
● This is why suspensions do not exhibit this type of movement.

27. ● This brownian motion arises due to the uneven distribution of the
collisions between colloid particle and the solvent molecules.
● Brownian movement was more rapid for smaller particles. It
decrease with increase the viscosity of the medium.

28. Diffusion
● Particles diffuse spontaneously from a region of higher
concentration to one of lower concentration until the
concentration of the system is equilibrium.
● Diffusion is a direct result of Brownian movement.

29. Ficks Ist law:
● states that particles diffuse spontaneously from a region of high
concentration to region of low concentration until diffusion
equilibrium is attained.
Where,
dq= quantity of drug diffused
D = diffusion coefficient
s = plane area
dc = concentration change
dx = distance travelled
dt = time taken for diffusion
● Application: molecular weight determination.
dq =-Ds (dc/dx) dt

30. Sedimentation
● The velocity v of sedimentation of spherical particles having a density 
in a medium of density o and a viscosity is given by stokes Law
Where,
v = rate of sedimentation
d= diameter of particles
 = density of internal phase and external phase
g= gravitational constant
 = viscosity of medium
v = d² (i- e)g/18

31. ● This law obeys only if the particles should be spherical Stokes
equation about only 5µm.
● Brownian movement becomes active sedimentation will becomes
slow due to gravity, promotes mixing.
● A strong force must be applied to bring sedimentation.
● Ultracentrifuge is used for the complete sedimentation.
● Ultracentrifuge can produce a force one million times that of
gravity.
Applications:
1. Molecular weight estimation
2. Study micellar properties of drug.

32. Osmotic pressure
● van't hoff equation:
π = cRT
● Can be used to determine the molecular weight of colloid in dilute
solution.
where c = the grams of solute / liter of solution
M = molecular weight
π/C = RT/M Kinetic Properties of Colloids
π = osmotic pressure
R= molar gas constant

33. Viscosity
● It is the resistance to flow of system under an applied stress.
● The more viscous a liquid, the greater the applied force required
to make it flow at a particular rate.
● The viscosity of colloidal dispersion is affected by the shape of
particles of the disperse phase
Spherocolloids dispersions of low viscosity
Linear particles more viscous dispersions

34. 4. Electric properties
● Surface charge
● Electrical double layer
● Zeta potential
a. Electrophoresis
b. Electro-osmosis
c. Sedimentation Potential (donnan effect)
d. Steaming Potential

35. Electrical double layer

36. Surface charge:
● The particles of a colloidal solution are electrically charged and carry the
same type of charge, either negative or positive.
● The colloidal particles therefore repel each other and do not cluster
together to settle down.
● The charge on colloidal particles arises because of the dissociation of the
molecular electrolyte on the surface.

37. Zeta Potential
● Zeta Potential is the electric potential at the
shear plane of a particle.
● Electrical double layer exists around each
particle which consists of two parts; an
inner region (Stern layer) where the ions
are strongly bound and an outer (diffuse)
region where they are less firmly
associated
● Within this diffuse layer is a notional
boundary within which the particle acts as a
single entity.
● The potential at this boundary is the zeta
potential

38. ● Particles within a colloidal dispersion carry charges that
contribute to the net charge of a particle. Used in predicting
stability of colloidal dispersion.

39. Electrophoresis
● The movement of colloidal particles towards a particular electrode
under the influence of an electric field.
● If the colloidal particles carry positive charge, they move towards
cathode when subjected to an electric field and vice versa.

40. Electro-osmosis
● It is the opposite in principal to that of electrophoresis.
● When electrodes are placed across a clay mass and a direct current
is applied, water in the clay pore space is transported to the
cathodically charged electrode by electro-osmosis.
● Electro-osmotic transport of water through a clay is a result of diffuse
double layer cations in the clay pores being attracted to a negatively
charged electrode or cathode.
● As these cations move toward the cathode, they bring with them
water molecules that clump around the cations as a consequence of
their dipolar nature.

41. ● The movement of dispersion medium under the influence of an electric field in
the situation when the movement of colloidal particles is prevented with the
help of a suitable membrane.
● During electrosmosis, colloidal particles are checked and it is the dispersion
medium that moves towards the oppositely charged electrode.

42. Sedimentation potential (Donnan effect)
● The sedimentation potential also called the ( Donnan membrane
effect).
● It is the potential induced by the fall of a charged particle under
an external force field.
● It is analogous to electrophoresis in the sense that a local electric
field is induced as a result of its motion.
● If a colloidal suspension has a gradient of concentration (such as
is produced in sedimentation or centrifugation), then a
macroscopic electric field is generated by the charge imbalance
appearing at the top and bottom of the sample column.

44. Streaming potential
● Differs from electro-osmosis in that the potential is created by forcing a
liquid to flow through a bed or plug of particles.

45. Effect of electrolytes in colloids
● Breakage of potential energy barrier leads to precipitation/
agglomeration.
● Instability Methods:
1. Reducing height of potential barrier.
2. Increasing the kinetic energy, reduces potential energy.
● Instability reasons:
1. Removal of electrolyte (1% minimum)
2. Addition of electrolyte (2%minimum)
3. Addition of electrolytes of opposite charge (2% minimum)
4. Addition of oppositely charged colloid (2% minimum).

46. 1.Removal of electrolyte (1% minimum)
Colloids + electrolytes ^stable colloidal dispersion
Dialysis = remove Electrolytes --- Particles coagulate ^Settle to bottom.
2. Addition of electrolyte (2% minimum)
Stable colloidal dispersion + excess electrolyte
electrolyte --- Accumulate ^instability.
3. Addition of electrolytes of opposite charge (2% minimum)
Stable colloidal dispersion + electrolyte opposite charge -- attractions between
particles ^ Flocculation of particles.
Schulze-Hardy Rule: Precipitating power a ionic charge
Al+3>Ba+2>Na+ S04 -2>Cl
4. Addition of oppositely charged colloid (2% minimum)
Bismuth colloids (+)+ Tragacanth colloids (-) Coagulation.

47. Stability of colloids
1- Addition of large amounts of electrolytes - Anions arranged in a
decreasing order of precipitating power:
citrate > tartrate > sulfate > acetate > chloride> nitrate > bromide >
iodide.
The precipitation power is directly related to the hydration of the ion
and its ability to separate water molecules from colloidal particles.
2- Addition of less polar solvent - e.g. alcohol, acetone The addition
of less polar solvent renders the solvent mixture unfavourable for the
colloids solubility.

48. Coacervation
● Coacervation is the process of mixing negatively and positively
charged hydrophilic colloids, and hence the particles separate from
the dispersion to form a layer rich in the colloidal aggregates
(coacervate).

50. Sensitization and protective colloidal action:
• Protection: the addition of large amount of hydrophilic colloid
(protective colloid) to a hydrophobic colloid tend to stabilize the
system.
• This may be due to:
The hydrophile is adsorbed as a monomolecular layer on the
hydrophobic particles.