Types of Colloidal Solutions

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In this article, we shall study types of colloidal solutions (systems) on the basis of states of the dispersed phase and dispersion medium, the interaction between the dispersed phase and dispersion medium, and on the number of atoms and molecules in a colloidal particle.

Types of Colloidal Solutions on the Basis of States of Dispersed Phase and Dispersion Medium:

A colloidal system is made up of a dispersed phase and a dispersion medium. Because either the dispersed phase or the dispersion medium can be a gas, liquid or solid. There are eight types of the colloidal system possible since gases are miscible, the gas colloidal system is not possible. Gas-gas systems always form true solutions.

Sr. No.	Dispersed Phase	Dispersion Medium	Name of Solution	Examples
1	Solid	Gas	Solid aerosol	Smoke, fumes, dust
2	Solid	Liquid	Sol	Blood, soap solution, gum, water paints, metal sols of Cu, Ag, Au in water,
3	Solid	Solid	Solid sol	Coloured glass, gems, metal alloys, steel, ruby, glass
4	Liquid	Gas	Liquid aerosols	Fog, mist, cloud, rain, insecticide sprays
5	Liquid	Liquid	Emulsion	Milk, cod liver oil, oil paints, creams, buttermilk, medicine, egg albumin, water in oil, oil in water
6.	Liquid	Solid	Gel	Jams, Jellies,  Badami halwa, curd, butter, cheese, boot polish, silica gel, gelatin, agar agar
7.	Gas	Liquid	Foam	Whipped cream of milk, soap lather. Foam, fire extinguisher
8	Gas	Solid	Solid foam	Pumice stone, sponge, cake, bread, rubber foam, biscuits, volcanic ash.

Classification of Sols On The Basis of  Interaction Between the Dispersed Phase and the Dispersion Medium:

A colloidal solution in which the dispersed phase is in solid-state and the dispersion medium is liquid is called a sol. e.g. Gum solution, the starch in water, Au, Ag, etc. in water, blood, etc.

Lyophilic Sols or Reversible Sols (Emulsoid):

The sols in which there is a strong affinity between the dispersed phase and dispersion medium are called as lyophilic sols. e.g. glue, gelatin, starch, proteins.

Characteristics of Lyophilic Sols:

• Lyophilic sols are readily formed by mixing together the substance forming disperse phase and solvent forming dispersion medium and heating the mixture if necessary.
• They are stable.
• There is a strong affinity between the dispersed phase and dispersion medium.
• The colloidal particles forming lyophilic sols are large single molecules or polymers like starch, proteins etc. of high molecular weight.
• If lyophilic sol is heated or dried we get solid but we get same sol if liquid (solvent or dispersion medium) is added to the solid. Thus lyophilic sols are reversible. After coagulation, they can again be converted into colloidal form.
• Lyophilic sols have lower surface tension than the dispersion medium.
• Lyophilic sols have a higher viscosity than dispersion medium.
• Stability of Lyophilic sols is due to high solvation due to the high affinity of particles towards dispersing medium.
• Lyophilic sols are stable and require a large quantity of electrolyte for coagulation. Thus they can not be coagulated easily.
• The particles cannot be detected easily under ultramicroscope.
• Lyophilic sols show weak Tyndall effect.

Stability of Lyophilic Sols:

In lyophilic sol, a thin film of the dispersion medium is formed around the dispersed phase colloidal particles due to the strong affinity between the dispersed phase and dispersion medium. The formation of this film around dispersed phase colloidal particles is called solvation. The stability of lyophilic sol is due to solvation.

Similarly, all the particles carry an electrical charge of the same nature, which results in mutual repulsion between the dispersed phase colloidal particles which also adds to the stability of lyophilic sol. But the charge on particles is very less or almost negligible.

Thus the stability of Lyophilic sols is due to solvation and charge on colloidal particles.

Lyophobic Sols or Irreversible Sols:

The sols in which there is no affinity between the dispersed phase and dispersion medium are called as lyophobic sols. e.g. sols of metals like Ag, Au, non-metals like sulphur, hydroxides like Al(OH)₃, Fe(OH)₃, sulphides like As₂S₃.

Characteristics of Lyophobic Sols:

• Lyophobic sols cannot be readily formed by mixing together the substance forming disperse phase and solvent forming dispersion medium.  Special methods like dispersion method or condensation method should be employed for making lyophobic sols.
• They are less stable.
• There is no or very little affinity between the dispersed phase and dispersion medium.
• The colloidal particles forming lyophobic sols are aggregates of a large number of atoms or molecules.
• If lyophilic sol is evaporated we get solid but we can not get the same sol if liquid (solvent or dispersion medium) is added to the solid. Thus lyophobic sols are irreversible. After coagulation, they cannot be converted into colloidal form again.
• Lyophobic sols have the same surface tension as the dispersion medium.
• Lyophobic sols have the nearly same viscosity as the dispersion medium.
• The stability of lyophobic sol is due to the charge on colloidal particles.
• Lyophobic sols are unstable and require a very small quantity of electrolyte for coagulation. Thus can be coagulated easily.
• The particles can be detected easily under an ultramicroscope.
• Lyophobic sols show a strong Tyndall effect.

Stability of Lyophobic Sols:

In lyophobic sols, all colloidal particles of the dispersed phase are either positively charged or negatively charged.

Colloidal particles remain suspended in the dispersion medium, without coagulation due to the repulsion between the particle having same nature of the charge,

Thus the stability of lyophobic sol is due to charge on colloidal particles.

Notes:

• If the dispersion medium is water then lyophilic and lyophobic sols are called hydrophilic and hydrophobic sols respectively.
• The colloidal solutions in alcohol and benzene are known as alcosols and benzosols respectively.
• The colloidal solutions in water are known as aquasols or hydrosols.

Classification of Colloidal Solutions on the Basis of the Number of Molecules or Atoms in the Colloidal Particle:

Multimolecular Colloids:

Multimolecular colloids are those systems in which the dispersed phase particles are aggregates of many atoms or molecules. The particles in these colloidal solutions are held together by van der Wall’s forces. e.g. gold sol particles are an aggregation of many gold atoms. other examples are silver sol and sulphur sol.

Macromolecular Colloids:

Macromolecular colloids are those systems in which the dispersed phase particles are a single macromolecule. They are lyophilic in character. e.g. sol of starch in water, Aqueous (Water) solution of proteins, enzymes.

Associated Colloids:

Colloids which behave as normal electrolytes at low concentrations, but exhibit colloidal properties at higher concentrations due to the formation of aggregated particles called associated colloids. The aggregated particles thus formed are called micelles.

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