Difference Between Lyophilic and Lyophobic Colloids

Main Difference – Lyophilic vs Lyophobic Colloids

A colloid is a type of homogeneous mixture where the dispersed particles do not settle out. Colloids show some unique properties such as Tyndall effect, Brownian motion, electrophoresis, etc. When colloids are present in a solution, it is known as a colloidal solution. These colloidal solutions can be categorized into two groups as lyophilic sols and lyophobic sols depending on the interaction between colloids and the liquid (solvent). Particles in lyophilic sols are lyophilic colloids, and particles in lyophobic sols are lyophobic colloids. The main difference between lyophilic and lyophobic colloids is that lyophilic colloids are thermodynamically stable whereas lyophobic colloids are unstable.

Key Areas Covered

1. What are Lyophilic Colloids
      – Definition, General Properties, Examples
2. What are Lyophobic Colloids
      – Definition, General Properties, Examples
3. What is the Difference Between Lyophilic and Lyophobic Colloids
      – Comparison of Key Differences

Key Terms: Brownian Motion, Colloid, Electrophoresis, Lyophilic Colloids, Lyophilic Sols, Lyophobic Colloids, Lyophobic Sols, Tyndall Effect

What are Lyophilic Colloids

Lyophilic colloids are solvent loving particles. In other words, they have a high affinity for the liquid they are dispersed in. When these colloids are mixed with a suitable solvent, a high attraction force arises between the solvent molecules and the colloid particles. Eventually, a very stable solution is formed, which is called a lyophilic sol.

If the solvent is water, then the lyophilic colloids that favor water are known as hydrophilic colloids. A lyophilic sol is highly stable because the attraction between the colloids and the liquid is quite strong. Since colloids are attracted to the liquid, precipitation or coagulation is minimum. If more particles are added, it can cause precipitation. But the initial stable sol can be regained by adding more solvent. Therefore, lyophilic sols have a reversible nature.

Figure 1: Gums are Composed of Lyophilic Colloids

Examples for compounds containing lyophilic colloids include gums, gelatin, starch solution, proteins, gels, etc. These lyophilic sols are highly viscous, and particles are not visible and cannot be detected easily.

What are Lyophobic Colloids

Lyophobic colloids are solvent hating colloids. There is no attraction between the colloids and the liquid. Lyophobic colloids are thermodynamically unstable. Therefore, these colloids tend to form aggregates or precipitate when added to a liquid. But the stability can be increased by adding a surface active agent to lower the interfacial energy of the system.

When water is used as the liquid, lyophobic colloids are known as hydrophobic colloids. A lyophobic sol can be prepared by specific mechanical methods. For example, mechanical agitation can be done. Lyophobic colloids readily precipitate or form aggregates when added to a liquid. Since they have no affinity for the liquid, the precipitation is irreversible.

Figure 2: Ferric Hydroxide is Lyophobic

Examples of lyophobic colloids include metals such as Ag, Au, hydroxides such as Ferric hydroxide, metal sulfides, etc.

Difference Between Lyophilic and Lyophobic Colloids

Definition

Lyophilic Colloids: Lyophobic colloids are solvent loving colloids.

Lyophobic Colloids: Lyophobic colloids are solvent hating colloids.

Stability

Lyophilic Colloids: Lyophilic colloids are thermodynamically stable.

Lyophobic Colloids: Lyophobic colloids are thermodynamically unstable.

Reversibility

Lyophilic Colloids: Precipitation in the lyophilic sol is a reversible process.

Lyophobic Colloids: Precipitation in the lyophobic sol is an irreversible process.

Interaction

Lyophilic Colloids: There is a strong attraction force between colloids and the liquid.

Lyophobic Colloids: There is less or no attraction between colloids and the liquid.

Viscosity

Lyophilic Colloids: Lyophilic colloids are highly viscous.

Lyophobic Colloids: Lyophobic colloids have the same viscosity as the solvent.

Formation of Sol

Lyophilic Colloids: Lyophilic colloids form a lyophilic sol.

Lyophobic Colloids: Lyophobic colloids form a lyophobic sol.

Water as the Solvent

Lyophilic Colloids: When water is taken as the solvent, lyophilic colloids are known as hydrophilic colloids.

Lyophobic Colloids: When water is taken as the solvent, lyophobic colloids are known as hydrophobic colloids.

Preparation

Lyophilic Colloids: A lyophilic sol can be prepared by the direct addition of dispersion phase (colloids) into dispersion medium (liquid).

Lyophobic Colloids: A lyophobic sol can be formed from special techniques such as mechanical agitation.

Conclusion

Colloids can be either lyophilic or lyophobic. Basically, lyophilic colloids are solvent loving particles, and lyophobic colloids are solvent hating particles. The main difference between lyophilic colloids and lyophobic colloids is that lyophilic colloids are thermodynamically stable whereas lyophobic colloids are unstable.

References:

1. “Materials Engineering.” Lyophilic and lyophobic colloids [SubsTech], 27 July 2013, Available here.
2. “Lyophobic Colloid.” Chemistry Learning, Available here.
3. “Lyophilic Colloids.” Chemistry Learning,  Available here.
4. “Preparation of Lyophilic and Lyophobic Sols”. Amrita Online Lab, Available here.

Image Courtesy:

1. “Natural gum of plum tree 01” By Rencas – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “Fe(OH)3” By Leiem – Own work (CC BY-SA 4.0) via Commons Wikimedia