# Tuning Permeability and Transport in Polyelectrolyte Membranes: The Role of Countercations

## TL;DR

This paper explores how different countercations affect the structure and permeability of polyelectrolyte multilayers, enabling control over transport properties for applications like drug delivery.

## Contribution

The study reveals the novel role of K+ countercations in enhancing film density and reducing permeability compared to Na+.

## Key findings

- K+-assembled films show higher mass, denser packing, and reduced permeability compared to Na+-assembled films.
- K+-films exhibit selected permeability toward ionic probes and frequency-dependent impedance behavior.
- Countercation choice influences drug release profiles in a model drug delivery system.

## Abstract

Polyelectrolyte multilayers (PEMs) are widely utilized
in membrane
technologies, biosensing, and drug delivery, where precise control
over permeability, which refers to the ease of transport through the
multilayer, is essential. While the influence of anions on PEMs is
well-documented, the role of countercations in regulating transport
properties through films remains underexplored. Here, we investigate
the effects of sodium (Na+) and potassium (K+) countercations on the formation, structure, permeability, and transport
properties of PAH/PSS and PDADMAC/PSS multilayers. Using a quartz
crystal microbalance with dissipation (QCM-D), atomic force microscopy
(AFM), cyclic voltammetry (CV), and electrochemical impedance spectroscopy,
we demonstrate that K+-assembled films exhibit higher mass,
denser packing, and significantly reduced permeability compared to
Na+-assembled films. Extended characterizations reveal
selected permeability toward ionic probes and frequency-dependent
impedance behavior in K+, underscoring the potential of
the films as tunable barriers. We further demonstrate their application
in a model drug release system, highlighting controlled release profiles
influenced by countercation choice. These findings provide insights
into cation-mediated tuning of PEM properties, offering a robust strategy
for designing advanced materials for separation, sensing, and biomedical
applications.