Beyond solution corrosion inhibitors tests: Evaluating the smart ion-exchange performance of CaAl LDH pigments within organic coatings

This study proposes a novel quantitative methodology to investigate the in situ release kinetics and barrier properties of “smart” ion-exchange pigments within organic coatings, addressing a critical methodological gap in active corrosion monitoring. Hydrothermally synthesized calcium‑aluminum layered double hydroxide (LDH) nanocontainers were intercalated with disodium sebacate (SB) inhibitor, yielding high-aspect-ratio (9.76) hexagonal platelets with a total inhibitor payload of 50 wt%. Thermogravimetric analysis confirmed exceptional thermal stability up to 700 °C driven by interlayer host-guest interactions. In aqueous solution, chloride scavenging followed a Langmuir chemisorption isotherm (R2 > 0.98) with near-instantaneous, diffusion-limited exchange kinetics. When incorporated into free-standing bilayer acrylic films using a custom two-chamber diffusion cell, the hybrid LDH/Seb2− system effectively mitigated the filler-induced defectivity observed in traditional nitrate-LDH counterparts. Total organic carbon and potentiometric monitoring revealed a highly synchronized, coupled mechanism: the active entrapment of permeating chlorides within the inorganic galleries simultaneously triggered a controlled, sigmoidal delivery of the organic inhibitor to the simulated substrate interface. Unlike free-SB controls that exhibited a detrimental “burst release,” the hybrid nanocontainers provided a gradual supply of inhibitor (55 ppm/cm2 after 28 days). Crucially, the intercalated dicarboxylate provided a structural pillaring effect that stabilized the Casingle bondAl framework against re-dissolution, ensuring permanent halide immobilization. Confining the active pigments within the primer layer beneath an unpigmented top-coat maximized the environment-to-interface delivery efficiency while preventing wasteful external leaching, demonstrating a highly optimized smart coating architecture for long-term active corrosion protection.