Difference between Lyophilic and Lyophobic Colloids

A colloid is a heterogeneous mixture of substances where very fine particles are dispersed in the dispersion medium. A colloid is an intermediate mixture between a homogeneous mixture known as a solution and the heterogeneous suspension. There are different types of colloids based on the state and interaction between the dispersed phase and dispersion medium. The three main types of colloids are:

  • Sol – solid in liquid
  • Gel – liquid in solid
  • Emulsion – liquid in liquid

Based on the interaction between the dispersion medium and dispersed phase, sols are classified into two types:

  • Lyophilic colloids or lyophilic sols – solvent-loving. In case of water as a dispersion medium, they are known as hydrophilic.
  • Lyophobic colloids or lyophobic sols – solvent-hating. When water is a dispersion medium, they are known as hydrophobic.

Lyophilic Colloids

In this type of colloidal system, the dispersed phase has a high affinity for the dispersion medium. They are also known as reversible sols due to their ability to reconstitute on adding dispersion medium after separation. They are quite stable and do not coagulate easily. Lyophilic sols are highly solvated and the particles of the dispersed phase are covered by a layer of the dispersion medium. They have the ability to protect lyophobic colloids from electrolytes. They form a protective layer around lyophobic particles. Lyophilic colloids can be coagulated by adding electrolyte or a suitable solvent. Examples of lyophilic colloids are gelatin, gum, starch, protein, rubber, etc.

Lyophobic Colloids

In this type of colloidal system, the dispersed phase does not have an affinity for the dispersion medium so the colloid is not readily formed. They are also known as irreversible sols as they cannot be reconstituted by simply adding dispersion medium after precipitation. They are unstable and can coagulate easily on adding electrolyte, shaking or heating. Lyophobic colloids can be prepared by special methods and require a stabilising agent. Examples of lyophobic colloids are metals and their insoluble compounds such as sulphides.

Difference between Lyophilic and Lyophobic Colloids

The table below shows the main differences between Lyophilic and Lyophobic Colloids or sols:

Lyophilic Colloids

Lyophobic Colloids

Affinity for the dispersion medium

High affinity, solvent attracting

No affinity, solvent repelling

Preparation

Easy to prepare just by mixing, shaking or heating substance with the dispersion medium

Require special methods to prepare and an electrolyte for stabilisation

Stability

Highly stable and do not coagulate easily on adding electrolytes

Unstable and can easily be coagulated by electrolytes

Reversibility

Reversible sols and can be reconstituted back by adding back the dispersion medium

Irreversible sols and once precipitated, they cannot be reconstituted back just by adding the dispersion medium

Solvation

Highly solvated, dispersed particles are covered by a layer of dispersion medium

Dispersed particles are not solvated

Effect of adding an electrolyte

Require a large amount of electrolyte for coagulation

Get coagulated even on adding a small amount of electrolyte

Viscosity

Highly viscous, more viscous than the medium

Viscosity is the same as that of the dispersion medium

Surface Tension

Generally less than that of the medium

Generally, the same as that of the medium

Examples

Starch, protein, gelatin, gum, etc. dissolved in water

Metals, metal sulphides and oxides

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