Absorption drying rate curves

In case (a), an equilibrium is reached. It can be considered here that there are only reversible physical interactions between the polymer and water. Drying leads to a curve that is practically a mirror image of the absorption curve. The behavior of the material can be characterized by two quantities the equilibrium water concentration W, which characterizes the polymer affinity for water (hydrophilicity), and the duration Id of the transient, which is sharply linked to the sample thickness L and to a parameter characteristic of the rate of transport of water molecules in the polymer - the diffusion coefficient D. 

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