Absorption properties of superabsorbent polymers

During the absorption process, the diffusion of water into the SAP is controlled by the affinity between the functional groups in the SAP and the molecules in the contacting fluid, where the swelling equilibrium is determined by the balance of three main forces. 

Free energy of the mixture of network chains and solvent. 

Osmotic pressure inside the network resulting from the mobility of counter ions surrounded hy the groups of permanent charge. 

Flexible network response or flexible swelling pressure. 

For SAPs with anionic groups on the main chain, the first two forces favor swelUng of gel, in contrast to force three. 

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