When two different concentrations of solution (or solution and pure solvent) are separated by a semipermeable membrane, the dilute solution (or solvent) diffuses (or transfers) through the semipermeable membrane to the concentrated solution. In the paper industry, it refers to the effect of the cooking liquor spreading through the surface of the wood chips.
Osmotic pressure
The permeation pressure of the solution occurs. It is equal to the mechanical pressure applied to the original solution to prevent the solvent from entering the solution. The thicker the solution, the greater the osmotic pressure of the solution. vice versa.
