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The below mentioned article provides study notes on Imbibition.
The absorption of water by the solid particles of an adsorbent causing it to enormously increase in volume without forming a solution is called imbibition. Solid substances or adsorbents which take part in imbibition are called imbibants, e.g., seeds, dry wood.
The liquid (usually water) which is imbibed is known as imbibate. The imbibate is held in between and over the surface of particles of the solid substance through the processes of capillarity and adsorption. Plant imbibants are hydrophilic (Gk. hydor— water, philein— to love) colloids.
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They have a highly negative water potential. As a result when they come in contact with water (yw = O), a steep water potential gradient is established. Water diffuses rapidly into the adsorbent. The process will continue till an equilibrium is established.
Amount of imbibition depends upon:
(i) Water potential gradient between adsorbent and water and
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(ii) Affinity of adsorbent for water. Imbibition increases the volume of the imbibant but the increase is less than the volume of water absorbed.
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It is caused by holding of water in between and over the surface of imbibant particles. Water molecules are immobilised. Their kinetic energy is released in the form of heat (heat of wetting). The swelling imbibant also develops a pressure called imbibition pressure (matric potential). Air dried Pea seeds on coming in contact with water can develop an imbibition pressure of up to 1000 bars (= 100 MPa).
This is tested by placing dry seeds in a tin, adding water up to their upper level and then tightly putting the lid over it. Within an hour the lid will be blown off. Alternately fill a gas jar % with dry seeds. Pour water up to the brim.
Cover the cylinder with lid and place a weight over the lid. Within a couple of hours the lid along with weight is lifted. Imbibition capacity is maximum in phycocolloids followed by proteins, starch and cellulose. Lignin is hydrophobic.
It, therefore, does not show imbibition of water. Imbibition is influenced by a number of factors like texture (looseness more and compactness less imbibition) of the imbibant, temperature (rises with rise of temperature), pressure (decreases if pressure is against imbibant), electrolytes (decreases) and pH (decreases or increases depending upon charge of imbibant).
Imbibition plays an important role in absorbing and retaining water:
(i) Absorption of water by young cells is mostly through imbibition,
(ii) Water is absorbed by the germinating seeds through imbibition,
(iii) Breaking of the seed coat in germinating seeds is due to greater imbibitional swelling of the seed kernel (starch and protein) as compared to seed coverings (cellulose),
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(iv) Seedling is able to come out of soil due to development of imbibition pressure,
(v) Imbibition pressure developed during germination of seeds and spores can break asphalt roads and concrete pavements,
(vi) Jamming of wooden frames during rains is caused by swelling of wood due to imbibition,
(vii) In older times, it was used in breaking the rocks and boulders. Wooden pegs were inserted in rocks. They were then made wet. As a consequence the wooden pegs developed huge imbibition pressures that could break the rocks into pieces,
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(viii) Fruits of many plants come to develop matric potential in addition to their osmotic potential in order to maintain inflow of water even under conditions of water scarcity.
