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

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.