part 10: DISPERSION SYSTEM

Dispersed Systems

Dispersed Systems

Dispersed phase + Dispersion medium

Dispersed phase

Internal or Discontinuous phase

Dispersion medium

External or Continuous phase

1. Molecular dispersion

2. Colloidal dispersion

3. Coarse dispersion

Classification of Dispersed Systems based on Particle Size

< 1nm

Size of Molecular dispersion

1nm - 0.5mcm

Size of Colloidal dispersion

> 0.5mcm

Size of Coarse dispersion

Monophasic

State of Molecular dispersion

Biophasic

State of Colloidal dispersion

Biphasic

State of Coarse dispersion

Invisible in electron microscope

Visibility of Molecular dispersion

Visible in electron microscope

Visibility of Colloidal dispersion

Visible under microscope

Visibility of Coarse dispersion

Molecular dispersion

Pass through ultrafilter and semipermeable membrane

Colloidal dispersion

Pass through filter paper, but no semipermeable membrane

Coarse dispersion

Do not pass through filter paper or semipermeable membrane

Rapid

Diffusion of Molecular dispersion

Slow

Diffusion of Colloidal dispersion

No diffusion

Diffusion of Coarse dispersion

1. Glucose

2. Oxygen molecules

3. Ordinary ions

Example of Molecular dispersion

1. Colloidal silver solution

2. Paint

3. Shaving cream

Example of Colloidal dispersion

1. Most pharmaceutical emulsions and suspensions

2. Grains of sand

3. Red blood cells

Example of Coarse dispersion

1. Lyophilic colloids

2. Lyophobic colloids

3. Association colloids

Types of Colloidal System

Lyophilic colloids

• Solvent loving colloids

• Thermodynamically stable

• Dispersion medium

  • Water: hydrophilic colloids

Organic molecules

Most lyophilic colloids are ________molecules

1. Dispersion of Starch

2. Gum

3. Protein in water

Example of Lyophilic colloids

Lyophobic colloids

• Solvent fearing colloids

• Thermodynamically unstable

• Dispersion medium

• Water: Hydrophobic colloids

• Consist of Inorganic particles dispersed in water

1. Dispersion of gold

2. Sulfur

3. Silver iodide in water

Example of Lyophobic colloids

Amphiphilic colloids

Association colloids are also known as?

Association colloids

Formed by the association (self-assemble or associate) of dissolved molecules (surfactants) of a substance to create particles of colloidal dimensions (most commonly termed Micelles)

Critical Micelle Concentration

The concentration of monomer at which micelles form

Aggreation number

The number of monomers that aggregate to form a micelle

Zsigmondy Gold number

Expression of the protective property of colloids

1. Solid

2. Liquid

3. Gas

What are the dispersion phases if the dispersion medium is Solid?

Solidsol

Colloid type if the dispersion medium and dispersion phase is Solid

1. Pearls

2. Opal

Example of Solidsol

Solid emulsion

Colloid type if the dispersion medium is Solid and the dispersion phase is Liquid

1. Cheese

2. Butter

Example of Solid emulsion

Solid foam

Colloid type if the dispersion medium is Solid and the dispersion phase is Gas

1. Pumice

2. Marshmallow

Example of Solid foam

1. Solid

2. Liquid

3. Gas

What are the dispersion phases if the dispersion medium is Liquid?

Sol, Gel

Colloid type if the dispersion medium is Liquid and the dispersion phase is Solid

1. Jelly

2. Paint

Example of Sol, Gel

Emulsion

Colloid type if the dispersion medium is Liquid and the dispersion phase is Liquid

1. Milk

2. Mayonnaise

Example of Emulsion

Foam

Colloid type if the dispersion medium is Liquid and the dispersion phase is Gas

1. Whipped cream

2. Shaving cream

Example of Foam

1. Solid

2. Liquid

What are the dispersion phases if the dispersion medium is Gas?

Solid aerosols

Colloid type if the dispersion medium is Gas and the dispersion phase is Solid

1. Smoke

2. Dust

Example of Solid aerosols

Liquid aerosols

Colloid type if the dispersion medium is Gas and the dispersion phase is Liquid

Clouds

Mist

Fog

Example of Liquid aerosols

1. Optical

2. Kinetic properties

3. Electrical properties

Properties of Colloids

Optical

Property of Colloids that is useful in obtaining information regarding:

• Shape

• Size

• Structure

• Molecular weight of colloids

Tyndall effect

When a beam is passed through a colloidal solution, some of the light may be scattered

1. Particle size

2. Shape

3. Interaction of colloidal materials

Light scattering measurements are used in estimating

Light scattering

Identify the property which is used to determine the molecular weight of colloids

a. Electric properties

b. Fluidity

c. Light scattering

d. Brownian movement

1. Brownian motion

2. Diffusion

3. Sedimentation

4. Viscosity

Kinetic properties

Brownian motion

• Random movement of colloidal particles

• Irregular, zigzag pattern movement

• Particle size = ↑ particle size = ↓ velocity

• Viscosity = ↑ viscosity = ↓ Brownian movement

Factors affecting Brownian motion

Diffusion

• Direct result of Brownian movement

• Can be expressed by Fick’s law

• ↓ Particle size = ↑ diffusion

• ↑ Temperature = ↑ diffusion

• ↓ Viscosity = ↑ diffusion

Factors affecting Diffusion

Sedimenation

Follows Stoke’s law

Viscosity

Resistance to flow of a system under applied stress

1. Shape of the dispersed phase

   1. Spherocolloids - ↓ viscosity

   2. Linear particles - ↑ viscosity

2. Size of particles

3. Molecular weight

4. Affinity of particles to the dispersion medium

Factors affecting Viscosity

Electrical properties

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

1. Zeta potential

2. Nerns’t potential

Electrical properties

Electrokinetic potential

Zeta potential is also known as?

Zeta potential

The difference in potential between the surface of the tightly bound layer (shear plane) and the electroneutral region of the solution

Electrothermodynamic potential

Nerns’t potential is also known as?

Nerns’t potential

Difference in potential between the actual surface and the electroneutral region of the solution

1. Electrophoresis

2. Electro-osmosis

3. Sedimentation potential

4. Streaming potential

Electrokinetic phenomena

Cataphoresis

Electrophoresis is also known as?

Electrophoresis

The movement of a charged particles through a liquid under the influence of an applied potential difference

Electro-osmosis

The movement of the dispersion medium under the influence of applied potential

Sedimentation potential

• Opposite of electrophoresis

• Creation of potential when particles undergo sedimentation

Streaming potential

Creation of potential by forcing a liquid to flow through a plug or bed of particles

Colloidal Copper

Colloidal preparation that is used as Cancer treatment

Colloidal Mercury

Colloidal preparation that is used as Syphilis treatment

Colloidal Gold

Colloidal preparation that is used as diagnostic agent for Paresis

Colloidal electrolytes

Colloid that increases solubility, stability and taste of certain compounds in aqueous and oily pharmaceutical preparations

Colloidal Sulfur

Colloidal preparation that is absorbed completely compared to coarsely powdered Sulfur

Sedimentation

This is used to determine the molecular weight of polymers

a. Viscosity

b. Sedimentation

c. Electric properties

d. Brownian movement

True

The velocity of the particles increases with decreasing particle size and increasing the viscosity of the dispersion medium decreases and finally stop the Brownian motion

a. True

b. False

Electric properties

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

a. Light scattering

b. Sedimentation

c. Electric properties

d. Brownian movement