Question

Give any two differences between lyophilic and lyophobic colloids?

Answer 1

Hint: Just as lipophilic (oil loving) and lipophobic (oil hating) substances are present, there are lyophilic and lyophobic colloids as well. However they are named so because of the nature of the interactive forces existing between the different types of particles present in the colloid.

Complete step by step solution:
> First let us understand about colloids:
Colloids refer to mixtures in which insoluble particles of one substance of size ranging from 1 to 1000 nm (called dispersed phase) are evenly dispersed in another substance (called continuous phase or dispersion medium). Examples of colloids include blood, clouds etc.
Colloids can be classified based on many factors such as physical state, dispersion medium, type of interactive forces between the particles and many more.
> On the basis of physical state:
- Solid solutions: here both the dispersed phase and the dispersion medium are solids.
- Aerosol: Air acts as a dispersion medium. Common example is clouds which consist of water droplets (dispersed phase) dispersed in air (dispersion medium).
- Gels: here the dispersed phase is liquid and the dispersion medium is solid. For example butter.
- Emulsion: here both the dispersed phase and the dispersion medium are liquid. They are of two types: (a) oil in water; example milk (b) water in oil; example vanishing cream.
> On the basis of interactive forces:
On the basis of the interactive forces between the dispersion medium and the dispersed phase they are divided are lyophilic colloids and lyophobic colloids.
> In lyophilic colloids, the particles of the dispersion medium have a strong affinity for the particles of dispersed phase. Due to this, the particles of the dispersed phase are solvated by the particles of the dispersion medium i.e. each particle belonging to the dispersed phase is surrounded by the monomolecular layer of the dispersion medium. Examples include gels.
> In lyophobic colloids, the particles of the dispersion medium and the dispersed phase do not interact with each other. Hence there is no solvation of the dispersed phase by the dispersion medium. Aerosols are lyophobic colloids.

> Hence the differences between lyophobic and lyophilic colloids are given below:

Lyophilic colloids	Lyophobic colloids
1. Their formation process is spontaneous and they are thermodynamically stable.	Their formation process is nonspontaneous since mechanical agitation is required in order to make them. Also they are thermodynamically unstable since the dispersed particles tend to aggregate.
2. Their viscosity is higher than that of their dispersion medium because of the solvation of the dispersed phase by the dispersion medium.	Their viscosity is the same as that of their dispersion medium.

Note: Since lyophobic colloids are thermodynamically unstable due to the weak interaction between the dispersed phase and dispersion medium which ultimately leads to the coagulation of the particles of the dispersed phase, small amount of surfactants are added them which lowers the interfacial energy of the dispersed particles.