• The shape of colloidal particles in dispersion is
important: The more extended the particle the greater its specific surface the
greater the attractive force between the particles of the dispersed phase and
the dispersion medium.

• Flow, sedimentation and osmotic pressure of the colloidal
system affected by the shape of colloidal particles.

• Particle shape may also influence the pharmacologic
action.

Classification of Colloids Based on the State of the Dispersed Phase and Dispersion Medium

Dispersion Medium

Dispersed phase

Type of colloid

Example

Gas

Liquid

Aerosol

Fog, clouds

Gas

Solid

Aerosol

Smoke

Liquid

Gas

Foam

Soda water

Liquid

Emulsion

Milk, hair cream

Liquid

Solid

Sol

Paints, cell fluids

Solid

Gas

Foam

Plastic foams

Solid

Liquid

Gel

Jelly, cheese

Solid

Solid Sol

Ruby glass

Types of colloids

• The nature of interaction between dispersed phase and
dispersion medium.

A-Lyophilic colloids
(solvent attracting) (solvent loving) – The particles in a lyophilic system
have a great affinity for the solvent.

• If water is the dispersing medium, it is often known as a
hydrosol or hydrophilic.

• Readily solvated (combined chemically or physically, with
the solvent) and dispersed, even at high concentrations; More viscid

• Examples of lyophilic sols include sols of gum, gelatin,
starch, proteins and certain polymers (rubber) in organic solvents.

• The dispersed phase does not precipitate easily

• The sols are quite stable as the solute particle
surrounded by two stability factors:

a- Negative or
positive charge

b- Layer of
solvent

• If the dispersion medium is separated from the dispersed
phase, the sol can be reconstituted by simply remixing with the dispersion
medium. Hence, these sols are called reversible sols.

• Prepared simply by dissolving the material in the solvent
being used e.g. dissolution of acacia in water.

B-lyophobic (solvent
repelling) (solvent hating) – The particles resist solvation and dispersion
in the solvent.

• The concentration of particles is usually relatively low.

• Less viscid

• These colloids are easily precipitated on the addition of
small amounts of electrolytes, by heating or by shaking

• Less stable as the particles surrounded only with a layer
of positive or negative charge

• Once precipitated, it is not easy to reconstitute the sol
by simple mixing with the dispersion medium. Hence, these sols are called
irreversible sols.

• Examples of lyophobic sols include sols of metals and
their insoluble compounds like sulphides and oxides. e.g. gold in water

C- Association /
amphiphilic colloids

• Certain molecules termed amphiphiles or surface active
agents, characterized by two regions of opposing solution affinities within the
same molecule.

• At low concentration:
amphiphiles exist separately (subcolloidal size)

• At high concentration: form aggregates or micelles (50 or
more

Association
colloids

Comparison
of colloidal sols

Lyophilic

Associated

Lyophobic

Dispersed phase (large organic mole. With colloidal size)

Dispersed phase (micelles of organic molec. Or ion – size
below the colloidal range)

Dispersed phase (Inorganic particles as gold)

Molec. of dispersed phase are solvated Formed
spontaneously

Hydrophilic and lyophilic portion are solvated , Formed at
conc. Above CMC

Not formed spontaneously

The viscosity ↑ with ↑ the dispersed phase conc.

The viscosity ↑ with ↑ the micelles conc.

Not greatly increase

Stable dispersion in presence of electrolytes

CMC↓ with electrolytes

Unstable dispersion in presence of electrolytes

Critical micelle
concentration (C.M.C): the concentration at which micelle form

• The phenomenon of micelle formation can be explained:

1- Below C.M.C: amphiphiles are adsorbed at the air/water
interface

2- As amphiphile concentration is raised: both the
interphase and bulk phase become saturated with monomers (C.M.C)

3- Any further amphiphile added in excess: amphiphiles
aggregate to form micelles

• In water: the
hydrocarbon chains face inwards into the micelle forming hydrocarbon core and
surrounded by the polar portions of the amphiphile associated with water
molecules.

• In non-polar liquid: the polar heads facing inward and the hydrocarbon
chains are associated with non-polar liquid.

• At concentrations close to C.M.C à spherical micelles

• At higher concentrations à
lamellar micelles

KRAFT POINT – The
temperature at which the solubility of surfactant = CMC (Micelle formation)

Shapes of
surfactant aggregates

Methods to
prepare Lyophobic colloids

A) Dispersion
methods:

Coarse particles are reduced in size to colloidal particles

1) Milling and
Grinding – Using Colloidal mill

• Substance ground to coarser form using a dispersion medium
– then passed through colloidal mill, that has two steel discs, having a small
aperture between them.

• These discs are rotated at high speeds in opposite
directions

• Process is repeated until the desired size is achieved

Colloidal mill

• Coarse to colloidal

• Material sheared between 2 rapidly oppositely rotating
close plates.

• Low efficiency & reduce the size of small proportion
of particles

• Stabilizers added to control the size (gums, gelatin)

• Eg: collidal kaolin, zno

2) Ultrasonic
Generator

• Dispersion achieved by High intensity Ultrasonic waves at
frequency more than 20,000 cycles/second that produce alternate cavity and
compression of the medium

• Stabilizers: surfactants are added to prevent reunion of
particles

3) Peptization

Breaking up of aggregates into colloidal sized particles

• Removal of electrolytes

• Addition of surfactants

Peptizing agents: glycerin, sugar, lactose – They promote
size reduction but don’t interfere

4) Electric arc
method – Bridge‘s arc method

• An electric current is struck betw two metallic electrodes
placed i container of water.

• The intense heat of the arc converts metal into vapours
which conden immediately in the cold water bath.

• This results in the formation of par of colloidal size.

• KOH – stabilizer

• Silver, platinum and Gold colloidal solutions

B) Condensation
methods –

Particles of sub colloidal range are made to aggregate into
colloidal particles

1) Chemical reaction

• For lyophobic colloids

• By oxidation, reduction or hydrolysis

• Eg: Sulphur solution is obtained by bubbling H2S gas
through the solution of an oxidizing agent like HNO3 or Br2 in water

• Only for inorganic substances

• Not used much in Pharmaceuticals currently

2) Addition of
non-solvent

• Concentrated alcoholic solution of S2 ——– Added into excess of water

• S2 present in molecular state in alcohol will precipitate
as finely divided particles

• These particles grow rapidly and form a colloidal
dispersion

• Why it grows – based on solubility – super saturation of
sulphur – either crystal growth or precipitation

• Crystallization – Nuclei growth and nucleation, but
nucleation will not be stable

• Molecules and ions adsorbed onto nuclei and forms
colloidal dimension

Colloids –
Properties

The main properties of Colloidal Solutions are as follows:

(1) Physical
properties

(i) Heterogeneous
nature: Colloidal sols are heterogeneous in nature. They consists of two
phases; the dispersed phase and the dispersion medium.

(ii) Stable nature:
The colloidal solutions are quite stable. Their particles are in a state of
motion and do not settle down at the bottom of the container.

(iii) Filterability:
Colloidal particles are readily passed through the ordinary filter papers. However
they can be retained by special filters known as ultrafilters (parchment
paper).

Optical
Properties of Colloids

1-Faraday-Tyndall
effect

• When a strong beam of light (IR light) is passed through a
colloidal sol, the path of light is illuminated (a visible cone formed)

• This phenomenon resulting from the scattering of light by
the colloidal particles

• This is due to interaction of particles with light

• This scattered beam is called as Tyndall beam

• Most visible when observed in dark

2- Electron
microscope

• Electron microscope is capable of yielding pictures of
actual particles size, shape and structure of colloidal particles

• Electron microscope has high resolving power, as its
radiation source is a beam of high energy electrons

Electron Microscope

3- Ultra Microscope –
Dark field microscope

4- Turbidity method

• Used to determine the concentration of dispersed particles
and molecular weight of solute

• By Spectrophotometer or Nephelometer

• Turbidity is measured based on the intensity of transmitted
light in Spectrophotometer

I/I₀ = e ^lt

• I₀ =
intensity of incident light

• I = intensity of
transmitted light

• l = length of
sample

• t = turbidity

• Turbidity is measured based on the intensity of scattered
light at right angles to the direction of incident light in Nephelometer

5- Light Scattering

• Used to study proteins, polymers and association colloids

• Spherical particles – light scattering in all directions

• Rod shaped particles – light scattering will be right
angle to direction of flow

• Turbidity is measured from scattered light at a particular
angle is given by equation

T = 16∏R/3

R = Intensity of incident and scattered light

R = Ir²/I_s

r = Distance from the scattered particle to point of
observation

T = Turbidity

• When light scattering due to random motion or difference
in refractive index, molecular weight is calculated by DEBYE equation

Hc / T = 1/M + 2Bc

T: turbidity

C: conc of solute in gm / cc of solution

M: molecular weight

B: interaction constant

H: constant for a particular system

Hc / T Vs Concentration gives STRAIGHT LINE, 2B is slope and
1/M is intercept

Kinetic
Properties of Colloids

1-Brownian motion

• Colloidal particles do not settle due to its size

• The zig-zag movement of colloidal particles continuously and
randomly due to thermal energy

• This brownian motion arises due to the uneven distribution
of the collisions between colloid particle and the solvent molecules and with
walls of container

• Brownian movement was more rapid for smaller particles

• It decrease with increase the viscosity of the medium

• Observed under light microscope

2- Diffusion

• Particles diffuse spontaneously from a region of higher
concentration to lower concentration until equilibrium is established

• Diffusion is a direct result of Brownian motion

• Fick’s first law used to describe the diffusion: The
amount of Dq of substance diffusing in time dt across a plane of area A is
directly proportional to the change of concentration dc with distance
traveled

dq = -DA (dc / dx) dt

D à
Diffusion coefficient

• The amount of the material diffused per unit time across a
unit area when dc/dx (conc. gradient) is unity

D à
Diffusion coefficient of a polymer and its molecular weight is estimated by the
formula

M = molecular weight

v = Partial specific volume of particles

N = Avagadro’s number

3- Osmotic pressure

– Van’t Hoff equation

π = cRT

• Can be used to determine the molecular weight of colloid
in dilute solution

• Replacing c by C / M (where C = the grams of solute /
liter of solution,

M = molecular weight)

π /C = RT/M

π = osmotic pressure; R=
molar gas constant

4- Sedimentation

• The velocity of sedimentation is given by Stokes‘Law:

dst = diameter of particles

ρs = density of solid

ρl = density of liquid

g = gravitational constant

η = viscosity of medium

h = height

t – time interval

5- 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 à
dispersions of low viscosity

Linear particles à
more viscous dispersions

Viscosity of
colloidal dispersion is influenced by

• Affinity of particles – Linear particles when kept in a
medium of low affinity viscosity decreases

• Type of colloids – Lyophilic colloids – more viscous than
dispersion medium

Lyophobic
colloids – equal viscosity of dispersion medium

• Molecular weight of particles – higher the molecular
weight, greater the viscosity

Electric
Properties of Colloids

• 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

• E.g. As2S3 has a
negative charge, During preparation of colloidal As2S3 , H2S is absorbed on the surface and
dissociate to H+ (lost to the medium) and S-2 remain on the surface of colloid

• Fe(OH)3 is positively charged, Due to self-dissociation
and loss of OH- to the medium, so they become [Fe(OH)3] Fe+3

• The distribution of ions of a charged particle is
explained by Electrical Double Layer

• When particles moves, this electrical double layer also
moves

• Electrical potential in the plane of shear of the charged
particle is called as ZETA POTENTIAL,
which is used to predict the stability surface of colloid

• Zeta potential is measured by Electrophoresis

Electrophoresis

• Electrophoresis is the most known electrokinetic phenomena

• It involves motion of charged particles through a fluid
under the influence of an applied electric field, using ELECTROPHORETIC CELL

• If an electric potential is applied to a colloid, the
charged colloidal particles move toward the oppositely charged electrode

• If the particle moves towards anode, the charge of the
particle is negative

• If the particle moves towards cathode, the charge of the
particle is positive

• Rate of migration depends on charge of particles

• As the particle is located at “Tightly Bound Layer”,
potential determined is ZETA POTENTIAL

• Sign and magnitude of migration can be determined

• As the potential gradient across the electrodes increases,
the velocity of migration of a particle increases

• Based on this Zeta potential is calculated by the formula

ɕ = v4
π ƞ/EƐ

E – Electric potential in volts; Ɛ – Dielectric constant

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

Sedimentation potential

• The sedimentation potential also called the Donnan 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

Passive
distribution – Donnan equilibrium

• The ratio of positively charged permeable ions equals the ratio
of negatively charged permeable ions

• Mathematically expressed:

• At equilibrium

Outside (o) Inside (I)

Na+ Na+

Cl- Cl-

R-

• Applying the condition of electroneutrality, the number of
positive charges must equal the number of negative charges on each side of the
membrane

• The presence of impermeable negatively charged molecules requires
more positively charged molecules inside the cell.

So Outside: [Na⁺]₀ = [Cl^–]_o
……………………… (1)

Inside: [Na⁺]_I = [R^–]_i+ [Cl^–]_I
……………………… (2)

• According to the principle of Escaping tendency of
electrolytes, concentrations must be equal.

[Na⁺]₀_*
[Cl^–]_o = [Na⁺]_i * [Cl^–]_i ……………………… (3)

Substituting equation 1 and 2 in 3, we get

[Cl^–]_{0 *} [Cl^–]_o = [Cl^–]_i{[R^–]_i
+ [Cl^–]_o}

[Cl^–]² _o = [Cl^–]²_i
+ [Cl^–]_I * [R^–]_I
……………………… (4)

Divide both sides by [Cl^–]²_i

Eq.5 , on rearrangement

……………………. (6) — Donnan Membrane Equilibrium

This equation is used to calculate the ratio of
concentration of diffusible anion outside and inside the membrane at
equilibrium

Stability
of colloids

• Stabilization serves to prevent colloids from aggregation

• The presence and magnitude, or absence of a charge on a colloidal
particle is an important factor in the stability of colloids

• Two main mechanisms
for colloid stabilization:

1-Steric stabilization
i.e. surrounding each particle with a protective solvent sheath which prevent
adherence due to Brownian movement

2-Electrostatic
stabilization i.e. providing the surface of particles with electric charge

A- Lyophobic Colloids

• Thermodynamically unstable and forms aggregates

• Explained by DLVO (Derjaguin, Landau, Verway, Overbeek)
Theory,

Particle-Particle
interactions

• Two types of interactions – Attraction and Repulsion

• Types of forces involved – Van der Waals forces of
attraction and Electrostatic repulsive forces

• Combination for both the above forces is Net Energy of
Interaction VT

Potential Energy Vs
Interparticle distance

Van der Waals forces of attraction

• Depends on chemical nature and size of the particle

• Forces cannot be altered easily

• Potential Energy is VA

Electrostatic
repulsive forces

• Depends on density, surface charges and thickness of bulk
layer Indicates the magnitude of Zeta Potential

• Potential Energy is VR

• Primary minimum
– particles are
very close –
Increase in potential
energy – Precipitation

• Secondary minimum –
particles are too long – Aggregation due to more attractive forces

• Net energy peak –
at intermediate distance – particles in Brownian motion – Good stability due to
positive Zeta potential – Can be estimated by height of maximum in potential
energy curve (VM)

• Value of VM is 10-20kt which is equivalent to 50 mV

Reasons for
Coagulation

• Removal of electrolytes – causes primary minimum

• Addition of excess electrolytes – results in accumulation
of opposite ions and decrease zeta potential

• Electrolytes of opposite charge – causes secondary
minimum. The charge and valency of
electrons are described by
“Hardy-Schulze Rule”

• Addition of oppositely charged electrolytes – Decrease in
ZP below 50 volts and causes secondary minimum

Hardy-Schulze Rule

• Coagulation of colloidal dispersions can be brought about
by addition of electrolytes which reduces the zeta potential

• The effectiveness of an electrolyte to cause precipitation
depends not only on concentration but also on the valence of the active ion

• The precipitating power of an ion on a dispersed phase of
opposite charge increases with the increase in valence or charge of the ion

• Greater is the valency of the oppositely charged ion of
the electrolyte being added, the faster is the coagulation

Eg: For ferric hydroxide colloid, phosphate ions are more
effective than sulphate ions

B- Lyophilic
association colloids

• Stable

• Present as true solution

• Addition of moderate amounts of electrolytes not cause coagulation
(opposite lyophobic)

• Stability is based on electrical charge and hydration

Reasons for
coagulation

1- Addition of large
amounts of electrolytes

• Anions arranged in a decreasing order of precipitating
power: citrate > tartrate > sulfate > acetate > chloride>
nitrate > bromide > iodide

• Cations = Mg > Ca > Ba > Na

• The precipitation power is directly related to the
hydration of the ion and its ability to separate water molecules from colloidal
particles

• When excess electrolytes are added ions get hydrated and
water is not available for hydration which leads to salting out or flocculation

2- Addition of less
polar solvents/nonsolvent

• e.g. alcohol, acetone

• Addition of this leads to dehydrated forms of lyophilic colloids
and stability depends on charge they possess

• It becomes unstable

3 – Addition of
oppositely charged colloids

• Shell of tightly bound water molecules prevents
flocculation

• Electrostatic attractions of oppositely charged particles
hold particle together

• Particles separate from the dispersion to form a layer
rich in the colloidal aggregates

Sensitization
and protective colloidal action

• Sensitization:
the addition of small amount of hydrophilic or hydrophobic colloid to a
hydrophobic colloid of opposite charge tend to sensitize (coagulate) the
particles

• Polymer flocculants can bridge individual colloidal
particles by attractive electrostatic interactions.

• For example, negatively-charged colloidal silica particles
can be flocculated by the addition of a positively-charged polymer

• Acacia with Gelatin

• Protection:
Addition of large amount of hydrophilic colloid (protective colloid) carrying
opposite charges to a hydrophobic colloid they tend to stabilize the system

• This is due to: hydrophilic colloid gets adsorbed to
hydrophobic particles and forms a protective layer around it

• This prevents coagulation by stopping the precipitating
ions reaching the colloidal particle

• The colloid which helps to stabilize the other colloid is
called as protective colloid and this property is expressed as GOLD NUMBER

GOLD NUMBER

• It is the measure of protective ability of hydrophilic
colloid

• Minimum weight in mgs of a protective colloid required to
prevent a color change from red to violet in 10ml of gold solution on addition
of 1ml of 10% NaCl solution

• Lower the gold number, more the protective action

Method of
determination of Gold Number

• Series of test tubes – 10ml of gold sol – add 1ml of 10%
NaCl solution

• At high conc. Gold sol dos not change its color – but at
low conc.

• Color changes from red to violet – test tube having min.
amt. of colloid which prevents the change in color is the gold number of the
protective colloid

• Eg: Albumin – 0.1, Sodium oleate – 3, Tragacanth – 2

Purification
of colloidal solutions

• When a colloidal solution is prepared is often contains
certain electrolytes which tend to destabilize it. The following methods are
used for purification:

1- Dialysis:

• Semipermeable cellophane membrane prevent the passage of
colloidal particles, yet allow the passage of small molecules or electrolytes

2- Electrodialysis

• In the dialysis unit, the movement of ions across the
membrane can be speeded up by applying an electric current through the
electrodes induced in the solution.

• The most important use of dialysis is the purification of
blood in artificial kidney machines.

• The dialysis membrane allows small particles (ions) to
pass through but the colloidal size particles (haemoglobin) do not pass through
the membrane.

Ultra filtration

• Colloidal particles an pass through ordinary filter paper
due to its pore size.

• Filter papers when impregnated with collodion
(Nitrocellulose) are called as “ULTRAFILTERS” where the pore size is reduced

• It removes all electrolytes and colloidal particles are
retained on the filter paper

• Collected and dispersed in a dispersion medium to get a
Sol

• Process is slow, so pressure or suction can be applied

Applications
of colloidal solutions

1- Therapy

• Colloidal system are used as therapeutic agents in
different areas.

e.g- Silver colloid-germicidal Copper colloid-anticancer
Mercury colloid-Antisyphilis

2- Stability

• e.g. lyophobic colloids prevent flocculation in
suspensions. e.g- Colloidal dispersion of gelatin is used in coating over
tablets and granules which upon drying leaves a uniform dry film over them and
protect them from adverse conditions of the atmosphere.

3- Absorption

• As colloidal dimensions are small enough, they have a huge
surface area. Hence, the drug constituted colloidal form is released in large
amount.

e.g- sulphur colloid gives a large quantity of sulphur and
this often leads to sulphur toxicity

4-Targeted Drug
Delivery

• Liposomes are of colloidal dimensions and are
preferentially taken up by the liver and spleen.

5- Photography

• A colloidal solution of silver bromide in gelatine is
applied on glass plates or celluloid films to form sensitive plates in
photography.

6- Clotting of blood

• Blood is a colloidal solution and is negatively charged.

• On applying a solution of Fecl3 bleeding stops and blood
clotting occurs as Fe+3 ions neutralize the ion charges on the colloidal
particles.

Summary

• 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

• Flow, sedimentation and osmotic pressure of the colloidal
system affected by the shape of colloidal particles.

• Particle shape may also influence the pharmacologic action

• Examples of lyophilic sols include sols of gum, gelatin, starch,
proteins and certain polymers (rubber) in organic solvents.

• The dispersed phase does not precipitate easily

• The sols are quite stable as the solute particle
surrounded by two stability factors namely – negative or positive charge and
layer of solvent

• Colloids are classified as lyophobic, lyophilic and
association colloids

• 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

• Flow, sedimentation and osmotic pressure of the colloidal
system affected by the shape of colloidal particles.

• Particle shape may also influence the pharmacologic action

• Examples of lyophilic sols include sols of gum, gelatin,
starch, proteins and certain polymers (rubber) in organic solvents.

• The dispersed phase does not precipitate easily

• The sols are quite stable as the solute particle
surrounded by two stability factors namely – negative or positive charge and
layer of solvent

• Colloids are classified as lyophobic, lyophilic and
association colloids

• The phenomenon of
micelle formation can
be explained as
: below C.M.C: amphiphiles are
adsorbed at the air/water interface, as amphiphile concentration is raised:
both the interphase and bulk phase become saturated with monomers and any
further amphiphile added in excess: amphiphiles aggregate to form micelles

• The main properties of colloidal solutions are Physical
properties, Heterogeneous nature, stable nature, Filterability

• Optical properties of colloids include Faraday Tyndall
effect, electron microscope and light scattering effect

• The phenomenon of micelle formation can be explained as:
below C.M.C: amphiphiles are adsorbed at the air/water interface, as amphiphile
concentration is raised: both the interphase and bulk phase become saturated
with monomers and any further amphiphile added in excess: amphiphiles aggregate
to form micelles

• The main properties of colloidal solutions are Physical
properties, Heterogeneous nature, stable nature, Filterability

• Optical properties of colloids include Faraday Tyndall
effect, electron microscope and light scattering effect

• 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 sedimentation potential also called the Donnan 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.

• Brownian motion – The zig-zag movement of colloidal
particles continuously and randomly.

• Diffusion – Particles diffuse spontaneously from a region
of higher conc. To one of lower conc. Until the conc. of the system is uniform
throughout

• Van’t Hoff equation =
π = cRT is used
to determine the molecular weight of colloid in dilute solution

• 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 sedimentation potential also called the Donnan 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.

• Stabilization serves to prevent colloids from aggregation.

• The presence and magnitude, or absence of a charge on a
colloidal particle is an important factor in the stability of colloids.

• Sensitization: the addition of small amount of hydrophilic
or hydrophobic colloid to a hydrophobic colloid of opposite charge tend to
sensitize (coagulate) the particles.

• Colloids are analysed by dialysis, electro dialysis and
ultrafiltration

• Colloidal system are used as therapeutic agents in
different areas.

• Stability – lyophobic colloids prevent flocculation in
suspensions.

• Coagulation of colloidal dispersions can be brought about
by addition of electrolytes which reduces the zeta potential

• Gold number is the measure of protective ability of
hydrophilic colloid and it is defined as minimum weight in mgs of a protective
colloid required to prevent a color change from red to violet in 10ml of gold
solution on addition of 1ml of 10% NaCl solution.

• Stabilization serves to prevent colloids from aggregation.

• The presence and magnitude, or absence of a charge on a
colloidal particle is an important factor in the stability of colloids.

• Sensitization: the addition of small amount of hydrophilic
or hydrophobic colloid to a hydrophobic colloid of opposite charge tend to
sensitize (coagulate) the particles.

• Colloids are analysed by dialysis, electro dialysis and
ultrafiltration

• Colloidal system are used as therapeutic agents in
different areas.

• Stability – lyophobic colloids prevent flocculation in
suspensions.

• Coagulation of colloidal dispersions can be brought about
by addition of electrolytes which reduces the zeta potential

Colloids

COLLOIDS

Dispersed systems

1- Molecular dispersions (less than 1 nm)

2- Colloidal dispersions (1 nm – o.5 um)

3- Coarse dispersions (> 0.5 um)

Classification of Colloids Based on Size

Size and shape of colloids

Classification of Colloids Based on the State of the Dispersed Phase and Dispersion Medium

Types of colloids

Association colloids

Comparison of colloidal sols

Shapes of surfactant aggregates

Methods to prepare Lyophobic colloids

A) Dispersion methods:

B) Condensation methods –

Colloids – Properties

(1) Physical properties

Optical Properties of Colloids

Kinetic Properties of Colloids

Electric Properties of Colloids

Electrophoresis

Electro-osmosis

Sedimentation potential

Passive distribution – Donnan equilibrium

Stability of colloids

A- Lyophobic Colloids

Particle-Particle interactions

Potential Energy Vs Interparticle distance

Van der Waals forces of attraction

Electrostatic repulsive forces

Reasons for Coagulation

Hardy-Schulze Rule

B- Lyophilic association colloids

Reasons for coagulation

1- Addition of large amounts of electrolytes

2- Addition of less polar solvents/nonsolvent

3 – Addition of oppositely charged colloids

Sensitization and protective colloidal action

GOLD NUMBER

Method of determination of Gold Number

Purification of colloidal solutions

1- Dialysis:

2- Electrodialysis

Ultra filtration

Applications of colloidal solutions

1- Therapy

2- Stability

3- Absorption

4-Targeted Drug Delivery

5- Photography

6- Clotting of blood

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Dispersed
systems

1- Molecular dispersions
(less than 1 nm)

2- Colloidal
dispersions (1 nm – o.5 um)

3- Coarse dispersions
(> 0.5 um)

Association
colloids

Comparison
of colloidal sols

Shapes of
surfactant aggregates

Methods to
prepare Lyophobic colloids

A) Dispersion
methods:

B) Condensation
methods –

Colloids –
Properties

(1) Physical
properties

Optical
Properties of Colloids

Kinetic
Properties of Colloids

Electric
Properties of Colloids

Passive
distribution – Donnan equilibrium

Stability
of colloids

Particle-Particle
interactions

Potential Energy Vs
Interparticle distance

Electrostatic
repulsive forces

Reasons for
Coagulation

B- Lyophilic
association colloids

Reasons for
coagulation

1- Addition of large
amounts of electrolytes

2- Addition of less
polar solvents/nonsolvent

3 – Addition of
oppositely charged colloids

Sensitization
and protective colloidal action

Method of
determination of Gold Number

Purification
of colloidal solutions

Applications
of colloidal solutions

4-Targeted Drug
Delivery