COLLOIDAL DISPERSION

Definition:- Colloidal dispersion is derived from two words colloidal+dispersion. "colloidal" means "colloid" and "dispersion" means "spreading".

The term colloid implies stickiness means (a glue-like substance in Greek) and a colloidal system is a dispersion phase which means internal phase and dispersed in the external phase.

And colloidal are polyphasic systems and the particle size of the colloidal system is (1nm-1mm) they are dispersed in a dispersion medium that is a large amount and called an external phase.

Dispersion phase+Dispersion medium=Colloidal (heterogeneous system) (glue-like).

Official preparation of colloidal system:-

The official preparation of the colloidal system is meant for parenteral use they are:-

1. Iron dextran injection (BP):-In this type of official preparation of colloidal system dextran complexes with ferric ions and used in the treatment of anaemia and are meant for intramuscular use.

2. Iron sorbitol injection:-This preparation is meant for intramuscular use and it is a complex of sorbitol, dextran, citric acid and ferric ions.

Application of colloidal dispersion:-

(1) Better compliance:-

•Easily swallowed by the children and elders

•Greater compliance can be achieved in the bitter dosage form.

(2) Thickening agent:-

•Used for preparation of industrial products like lotion, toothpaste, and lubricants, and also used in coating etc.

(3) Colloidal system used for therapy:-

The colloidal system also shows therapeutic effects or action for example:-

Silver -Germicidal

Copper -Anticancer

Mercury -Antisyphilis

(4) Excipients:-

This system is used as vehicles, carriers product components for all routes of administration.

(5) Absorption and toxicity:-

Colloidal sulfur gives better absorption compared to coarse dispersion.

Classification of colloidal dispersion:-

Colloidal systems are classified into three types such as:-

(1)Based upon the state of matter

(2)Based upon Nature and properties 

(3)Based on particle size

(1) Based upon the state of matter:-According to based upon the state of matter colloidal systems are classified into 8 types they are:-

Dispersed phase	Dispersion medium	System	Example
Solid	Solid	Solid Sol	Colloidal gold
Liquid	Solid	Gels	Wax, gel
Gas	Solid	Solid foams	Foams, rubber
Solid	Liquid	Sols	Paints
Liquid	Liquid	Emulsion	Milk, cream
Gas	Liquid	Aerosols	Smoke, fog
Solid	Gas	Solid foams	Pumicestone
Liquid	Gas	Aerosols in liquid	Moisture

(2) Based upon the Nature of the colloidal system:-On the basis of the interaction (nature) of dispersed particles is classified into three types they are:-

1. Lyophilic colloids

2. Lyophobic colloids

3. Association colloids

1. Lyophilic colloids:-

•Derived from two words "do" means "solvent" and "philia" means"loving" so it is a solvent-loving solvent.

•Greater affinity with the dispersion medium.

•Colloidal particles having a sheath around by forming of dispersion medium (solvent).

•Lyophilic colloidal are two types:-

1. Hydrophilic:-(Water soluble)

•Such as acacia, gelatin and insulin etc.

2. Lipophilic:-(Lipid soluble)

•Such as rubber and polystyrene.

Example:-Acacia, Gelatin, and starch are dispersed in water.

2. Lyophobic colloids:-

•Derived from two words "do" means "solvent" and "phobic" means "hating" so lyophobic is solvent hating.

•Stable system because of the presence of a charge on the particle.

•In this system solvent sheaths around the particle are absent.

•They are thermodynamically unstable systems. I 

Example:-Gold, Silver, Sulfur, Arsenious sulfide and silver iodide in water etc.

3. Association colloids:-

•Amphiphiles are molecules or ions.

•They have a certain affinity for both polar and nonpolar solvents.

•In this type of colloid formation of "micelles".

•CMC- The critical micelle concentration

•If the low concentration of amphiphile (<CMC) surface is unsaturated.

•If amplitude concentration (=CMC) surface saturated monomolecular layer.

(3) Based upon particle size and properties:-According to based upon particle size and properties of different types of colloidal dispersion systems divided into three types they are:-

1. Molecular Dispersion

2. Colloidal Dispersion

3. Coarse Dispersion

Characteristics Properties	Molecular dispersion	Colloidal dispersion	Coarse dispersion
Particle size range	(only less than 1 nm)<1 nm="" td="">	1nm to 1000nm	>1mm
Diffusion rate	Rapid	Very slow	Not diffusion
Settling of particle	Not setting	Under centrifugation	Under gravity
Appearance	Transparent	Claudy	Opaque (claudy)
Brownian motion	Negligible	Show	May be/may not be
Visibility	Invisible in electron microscope	Visible under electron microscopes	Visible under normal microscopes
Separation	Not possible	Through semipermeable membranes	Through filter paper
Nature	Homogeneous	Heterogeneous	Heterogeneous
Tyndall effect	Don't show	Show	Show
Example	Oxygen and other gases	Cheese, milk, butter, blood etc	Suspension

Properties of colloids:-There are mostly three properties of colloids they are:-

1. Optical Properties:-

•Light microscopes

•Turbidity

•Ultramicroscope

•Light scattering

•Electron microscopes 

2. Kinetic properties:-

•Diffusion 

•Brownian motion

•Viscosity

•Sedimentation

3. Electrical properties:-

•Effect of electrolyte

•Electrical double layer (Zeta potential)

•Protective colloids

•Gold number 

Information:- We will continue this article in part two with a deep explanation of colloid properties that are optical, kinetic and electrical.

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