About different types of water in swollen polyelectrolyte multilayers

Area of Science:

• Materials Science
• Polymer Science
• Physical Chemistry

Background:

• Polyelectrolyte multilayers (PEMs) are versatile materials with applications in coatings, drug delivery, and sensing.
• Understanding water uptake in PEMs is crucial for predicting their behavior in aqueous environments.
• Existing models for water content determination in PEMs require further refinement.

Purpose of the Study:

• To compare different models for determining water content in swollen polyelectrolyte multilayers.
• To differentiate between water residing in pre-existing voids and water causing layer expansion.
• To investigate the influence of preparation conditions on the ratio of different water species.

Main Methods:

• Review and comparison of existing theoretical models for water content analysis.
• Analysis of scattering length density and thickness changes during swelling.
• Correlation of water content with preparation parameters such as polymer type, charge density, ionic strength, and salt type.

Main Results:

• Dry-state voids within PEMs act as reservoirs for "void water", contributing to total water content without altering layer thickness.
• "Void water" primarily affects scattering length density, not thickness, during swelling.
• "Swelling water" causes significant changes in both scattering length density and thickness.
• The proportion of "void water" (1-15 vol.%) and "swelling water" (tens of vol.%) is highly dependent on preparation conditions.

Conclusions:

• A clear distinction between "void water" and "swelling water" is essential for accurate modeling of PEM hydration.
• Preparation conditions significantly influence the partitioning of water within PEMs.
• This understanding is critical for designing PEMs with tailored properties for specific applications.