# Polyelectrolyte Microcapsule Stability: Non-Monotonic Layer-Dependent Desorption Kinetics of Poly(allylamine hydrochloride)

## TL;DR

This study examines how the number of layers in polyelectrolyte microcapsules affects the release of a polymer called PAH, finding that the core material and layer count influence release behavior in complex ways.

## Contribution

The study reveals a non-monotonic relationship between layer number and PAH desorption kinetics in CaCO3-templated microcapsules.

## Key findings

- CaCO3-templated PMCs with 9 layers showed maximal kinetic amplification of PAH release.
- MnCO3-templated PMCs exhibited uniform low initial dissociation regardless of layer number.
- Core template type is the dominant factor controlling PAH desorption kinetics.

## Abstract

Polyelectrolyte microcapsules (PMCs) fabricated by layer-by-layer assembly require predictable shell stability for applications in drug delivery, biosensing, and environmental remediation. While core template type is known to influence stability, the role of polyelectrolyte layer number in governing poly(allylamine hydrochloride) (PAH) desorption remains poorly understood. This study quantitatively assessed PAH desorption from fluorescein isothiocyanate (FITC)-labeled shells of PMCs templated on CaCO3 or MnCO3 cores with 7, 9, or 13 layers under varying ionic conditions (distilled water, NaCl 0.2–3.0 M, Na2SO4 0.005–1 M) over 168 h. Short-term incubations revealed no significant layer-dependent desorption differences for either core type. However, prolonged exposure uncovered a non-monotonic relationship for CaCO3-templated PMCs: 7-layer capsules exhibited high initial but limited subsequent release (<50% increase), 9-layer capsules showed minimal initial dissociation followed by maximal kinetic amplification (up to 2000% increase), and 13-layer capsules displayed intermediate behavior. In contrast, MnCO3-templated PMCs demonstrated uniformly low initial dissociation with gradual time- and concentration-dependent release irrespective of layer number. These findings establish core template nature as the dominant factor controlling dissociation kinetics, while layer number enables fine-tuning of release profiles—particularly for CaCO3 systems—providing design principles for controlled-release applications requiring delayed or sustained payload delivery.