About different types of water in swollen polyelectrolyte multilayers

• Correct determination of water content of polyelectrolyte multilayer (PEM)
• Identification of void water, which does not contribute to volume changes
• Relationship between void water and swelling water and the structure of PEM
• Relationship between odd/even effect and water distribution across PEM
• Effect of different preparation parameters on the different types of water

The review addresses swelling of polyelectrolyte multilayers in water. Different models for the determination of the water content are compared. It is clearly shown that voids under dry conditions present cavities for water which contribute to the water content of the multilayer in the swollen state. This so-called “void water” does not lead to any changes in thickness but in scattering length density during swelling. The “swelling water” leads to both changes in scattering length density and in thickness. Depending on the preparation conditions like the type polymers, polymer charge density, ionic strength and type of salt the ratio of “void water” differs between 1 and 15 vol.% while the amount of “swelling water” is of several ten's of vol.%.

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