Salt-Induced Diffusion of Star and Linear Polyelectrolytes within Multilayer Films

Area of Science:

• Polymer Science
• Materials Science
• Physical Chemistry

Background:

• Layer-by-layer (LbL) films are versatile materials with tunable properties.
• Understanding polyelectrolyte diffusion within LbL films is crucial for their application.
• Molecular architecture influences polymer behavior in confined environments.

Purpose of the Study:

• To investigate the effect of salt concentration on polyelectrolyte diffusivity in LbL films.
• To compare the diffusion behavior of linear and star-shaped polyelectrolytes.
• To correlate molecular architecture with salt-induced changes in polymer mobility.

Main Methods:

• Synthesis of linear, 4-arm, 6-arm, and 8-arm poly(methacrylic acids) (PMAA) via atom transfer radical polymerization.
• Assembly of PMAA with poly[2-(trimethylammonium)ethyl methacrylate chloride] (QPC) into LbL films.
• Neutron reflectivity (NR) to measure perpendicular diffusion and fluorescence recovery after photobleaching (FRAP) for parallel diffusion.

Main Results:

• Neutron reflectivity revealed a ~10-fold increase in polycation mobility for 8-arm PMAA/QPC films in 0.25 M NaCl compared to linear PMAA/QPC films.
• FRAP experiments showed star PMAAs diffused slower than linear PMAA below ~0.22 M NaCl.
• A crossover in mobility was observed, with star polymers exhibiting higher diffusion rates in more concentrated salt solutions.

Conclusions:

• The molecular architecture of polyelectrolytes significantly affects their diffusion dynamics in LbL films under varying salt conditions.
• Star-shaped polymers exhibit a more pronounced response to salt concentration changes compared to linear polymers.
• Findings provide insights into theories governing polyelectrolyte diffusion in multilayered systems and coacervates.