Interfacial co-assembly of CO2-responsive rosin-based surfactant and CNF in gel emulsions for encapsulation and release of tea tree oil.

Tea tree oil (TTO) possesses valuable antibacterial and antioxidant activities but suffers from high volatility and instability. Here, a CO₂-responsive Pickering gel emulsion (PGE) was developed using a rosin-based surfactant (RMN) and cellulose nanofibers (CNF) to enhance TTO encapsulation and controlled release. RMN undergoes reversible CO₂/N₂-induced protonation, enabling tunable interfacial electrostatic co-assembly and stabilizing the PGE structure. The RMN/CNF system achieved 85% TTO encapsulation efficiency and sustained release for 72 h, following the Korsmeyer-Peppas model (n = 0.61). SEM and rheology confirmed a dense 3D fiber-droplet gel network with solid-like viscoelastic properties, contributing to long-term stability exceeding 3 months. Antioxidant activity (>80%) and antibacterial performance against E. coli and S. aureus were well retained. This study reveals the synergistic stabilization mechanism between RMN and CNF and provides a sustainable, stimuli-responsive platform for delivering volatile natural actives.