Film stability during postassembly morphological changes in polyelectrolyte multilayers due to acid and base exposure

Area of Science:

• Materials Science
• Polymer Chemistry
• Surface Science

Background:

• Polyelectrolyte multilayers (PEMs) are versatile thin films constructed via layer-by-layer assembly.
• Understanding PEM morphology is crucial for designing functional materials.
• Weak polyelectrolytes in PEMs are susceptible to pH-induced structural changes.

Purpose of the Study:

• To investigate the mechanism of morphological transitions in PEMs composed of weak polyelectrolytes.
• To differentiate the effects of acidic and basic post-assembly treatments on PEM structure and porosity.
• To elucidate the relationship between pH, structural rearrangement, and film stability.

Main Methods:

• Layer-by-layer (LbL) assembly of polyelectrolyte systems (LPEI/PAA, PAH/PAA).
• Post-assembly treatment with acidic and basic solutions.
• Morphological analysis using Atomic Force Microscopy (AFM), optical microscopy, Scanning Electron Microscopy (SEM).
• Film mass and component release monitoring via Quartz Crystal Microbalance (QCM) and Fourier-Transform Infrared (FTIR) spectroscopy.

Main Results:

• Both acidic and basic treatments induced porosity in PEMs, with distinct morphological outcomes.
• Increased porosity, film collapse, and dissolution were observed under varying pH conditions and exposure times.
• Structural reorganization, linked to polycation neutralization and polyanion ionization, drives morphological changes.
• FTIR and QCM confirmed selective or partial release of polyelectrolytes in response to pH.

Conclusions:

• pH-driven structural reorganization is a key mechanism governing weak polyelectrolyte PEM morphology.
• Post-assembly pH treatments offer tunable control over PEM structure, porosity, and stability.
• Findings provide valuable insights for the rational design of functional polyelectrolyte-based materials.