A very significant property of hydrophilic surfaces is the adsorption of water molecules, a process called imbibition.
The phenomenon of imbibition has three important characteristics :
1. Volume change : In the course of imbibition the volume of the system increases i.e., swelling occurs. The total volume of the water imbibed plus the imbibing material is less after imbibition than before. Evidence indicated that there is an actual compression of water i.e., water molecules on being arranged on the surface of the imbibant, occupy less volume than the same molecules do when they are free in the normal liquid.
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2. Production of heat : As the water molecules are arranged on the surface of the imbibant they loose some of their kinetic energy which then appears as heat in the system.
3. Development of Pressure : If an imbibing system is confined, great pressure may be developed by the swelling. This can be mechanically demonstrated in laboratory.