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

Aliaksei Aliakseyeu; Parin Purvin Shah; John F Ankner; Svetlana A Sukhishvili

doi:10.1021/acs.macromol.3c00777

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

Macromolecules. 2023 Jul 10;56(14):5434-5445. doi: 10.1021/acs.macromol.3c00777. eCollection 2023 Jul 25.

Authors

Aliaksei Aliakseyeu¹, Parin Purvin Shah¹, John F Ankner², Svetlana A Sukhishvili¹

Affiliations

¹ Department of Materials Science & Engineering, Texas A&M University, College Station, Texas 77843, United States.
² Spallation Neutron Source Second Target Station Project, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States.

Abstract

This study explores the effect of salt on the diffusivity of polyelectrolytes of varied molecular architecture in layer-by-layer (LbL) films in directions parallel and perpendicular to the substrate using fluorescence recovery after photobleaching (FRAP) and neutron reflectivity (NR) techniques, respectively. A family of linear, 4-arm, 6-arm, and 8-arm poly(methacrylic acids) (LPMAA, 4PMAA, 6PMAA, and 8PMAA, respectively) of matched molecular weights were synthesized using atom transfer radical polymerization and assembled with a linear polycation, poly[2-(trimethylammonium)ethyl methacrylate chloride] (QPC). NR studies involving deuterated QPC revealed ∼10-fold higher polycation mobility for the 8PMAA/QPC system compared to all-linear LbL films upon exposure to 0.25 M NaCl solutions at pH 6. FRAP experiments showed, however, that lateral diffusion of star PMAAs was lower than LPMAA at NaCl concentrations below ∼0.22 M NaCl, with a crossover to higher mobility of star polymers in more concentrated salt solutions. The stronger response of diffusion of star PMAA to salt is discussed in the context of several theories previously suggested for diffusivity of polyelectrolyte chains in multilayer films and coacervates.