Why do we feel cool when we apply nail polish on nails?

We feel cool when we apply nail polish on nails due to the rapid evaporation of solvent present in the nail polish which is volatile in nature. As the solvent in the nail polish gets evaporated, we feel cold on our nails.

Nail polish primarily contains nitrocellulose which is dissolved in a solvent called as butyl acetate (or ethyl acetate). As the butyl acetate evaporates the nitrocellulose forms a shiny layer on our finger and the pigments present in the nail polish add color to the shiny layer. The color of the pigment depends on its chemical composition.

During this entire process, the evaporation of butyl acetate causes a sensation of coldness on our nails.

 

Why do they add solvents in nail polish?

Solvents help in uniform distribution of pigments and other ingredients of nail polish. Once the nail polish is applied to nails, the solvent evaporates leaving behind the thick coat of polish. It is the type of solvent which determines the thickness of coat and time for drying of polish.

This curious question comes under the topic – Evaporation

 

What is Evaporation?

Evaporation is the process by which a substance in liquid phase converts into gaseous phase at temperature below the boiling point of the liquid at given pressure. It is also a surface phenomenon, which means the process takes near the surface of the liquid.

 

Why Evaporation is a cooling process?

We learned that evaporation is the process by which a substance in liquid phase converts into the gaseous phase. Thus in order to change from liquid state to gaseous state, it requires energy. When the liquid absorbs that energy in the form of heat from the surroundings, the surroundings tend to become colder relative to liquid producing a cooling effect.

This can be explained using an example

Consider some water is poured on a floor; the heat energy present on floor gradually gets absorbed by water increasing its kinetic energy. As the kinetic energy of the liquid (water) increases the liquid (water) tries to fly off from the vicinity of the liquid. When this happens we say the liquid is converted into vapor or gas. Since heat energy from the floor was converted to kinetic energy, the floor losses heat and becomes cold. (We know that absence of heat is coldness).

Since the liquid is converted to gas (Evaporation) in this process by absorbing heat, we can say that evaporation is a cooling process.

 

Uses of Evaporation in daily life

1. Coolers and cooling towers work on the principle of Evaporation.

2. Salt is prepared naturally by evaporation of sea water. As the sea water gets evaporated from the ground, the salt is left behind.

3. We use fan to dry the wet floor, this uses the principle of evaporation.

4. Water from Cloths gets evaporated when placed in Sun.

5. Sweat on our body makes us feel cool due to evaporation.

Comment more examples below

Why petrol evaporates faster than water?

 

This Explanation also applies to

Why does nail polish remover feel cold on our skin?

Acetone is the main ingredient of nail polish remover which is highly volatile in nature. This volatile nature of acetone causes it to evaporate quickly on the surface of our skin which causes a cooling effect.

Cheap and simplest nail polish remover contains about 90% acetone and 10% water. However, nail polish remover available in the market comes in different proportions of these chemicals. The original composition of nail polish remover is given below:

 

Composition of Standard Nail Polish Remover

Acetone – 30-60%

Ethyl Acetate – 10-35%

Ethyl Alcohol – 5-20%

Water – 5-20%

Glycerin – 3-15%

Source: US Patents – US4735798A

 

Since Acetone is more volatile than butyl acetate (solvent present in nail polish), we feel colder when we apply nail polish remover than nail polish itself.

Butyl acetate has very low volatility.

 

References

Nail Polish Remover Google Patents

Butyl acetate | C6H12O2 – PubChem

Nail Polish -Wikipedia

Evaporation – Wikipedia

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