Adsorb vs Absorb

“Adsorption” and “Absorption”– Many have assumed that these terms are similar. However, is that so?

Let’s start by defining the terms.

Absorption – “The process whereby the atoms, molecules, and ions enter a solid, gas, or liquid material and are chemically integrated into one another.” However, Adsorb is when a physical bond is holding the molecules of a fluid stick on a solid or liquid surface. It involves adhesion, unlike absorption, which requires dissolution or diffusion.

Are we getting a little too technical?

Imagine a scenario where you’re getting a new house, and you have decided to apply a fresh coat of paint. You painted the wall with your new favourite colour, and it sits nicely on the wall. That’s adsorption – a fluid forming a layer on the surface. While painting, you’ve accidentally toppled the tin of paint, you hurriedly took a piece of towel to wipe it off. The process whereby the paint is transferred from the floor to the towel is called absorption – when something penetrates an object.

Does Desiccant Adsorb or Absorb?

Desiccants are drying agents that remove excess moisture from the surrounding environment. A common desiccant widely used is Silica Gel – the sachet of beads found in your bags to prevent mould growth. Many users claim that desiccants absorb moisture. However, there isn’t any chemical reaction being formed between the moisture and desiccant. Instead, moisture simply clings to the surface of the desiccant, forming a physical bond, making it an adsorption process.

Adsorption of moisture is typically a process whereby desorption can happen by introducing heat. Hence, moisture adsorbed can be released back to the environment when the desiccant is heated to a specific temperature. Therefore, it is always important to understand the type of desiccant you are using to achieve the best result! The next time someone says that desiccant absorbs moisture, tell them otherwise!