Imbibition is basically a unique kind of diffusion that takes place when the solids absorb or come in contact with water resulting in huge increase in their volume. An apt example of this would be the absorption of water by the seeds. It is the pressure exerted due to imbibition that the seedlings emerge out of the soil else they might not be able to rise.
Imbibition is also known to be diffusion as water movement is alongside a concentration gradient. The seeds as well as other such stuff do not have any water and thus they absorb it with ease. For imbibitions, the water potential gradient amid the absorbent and the liquid imbibed is necessary. In addition to this, in order for any substance to imbibe liquid, likeness between the absorbent and the liquid is also essential.
Imbibition happens when a wetting fluid moves a non-wetting. It should not be confused with drainage wherein a non-wetting phase moves the wetting fluid. Both these processes are ruled by different mechanisms. One of the examples of imbibition imbibed in nature is the assimilation of water by hydrophilic colloids. Matrix potential contributes to water in substances such as these. Many biological substances possess the property of imbibition. However, different kinds of substances have different imbibing capabilities. Some substances such as proteins include a high imbibing capacity, starch on the other hand have low imbibing capacity and cellulose has the least capacity. This is the reason why on imbibition, the protein-rich pea seeds swell more than the starchy wheat seeds.
Imbibitional pressure created due to water can have terrific magnitude. This can be explained by splitting of rocks by inserting dry wooden stalks in their crevices and soaking them in water. During the early times, this method was used by Egyptians to cut big stone blocks.