Chitosan-capped mesoporous silica nano/microcontainers for waterborne epoxy coating: Implications of size and textural properties modulated by synthesis route

Herein, the dependence of the performance of smart waterborne epoxy coating on the size and textural properties of intercalated nano/microcontainers is critically examined. Two routes were adopted to synthesize nano/microcontainers from similar starting materials resulting in nanocontainers and microcontainers with dissimilar textural properties. The containers were constructed based on mesoporous silica particles (MSPs) loaded with benzotriazole (BTA) and encased with chitosan (CTS) shell to obtain nanocontainers with a slightly crystalline core (C@B@MSP1) and microcontainers with amorphous core (C@B@MSP2), both demonstrating pH-responsiveness. The obtained containers were characterized using SEM, TEM/EDX, XRD, FTIR, TGA, XRD, N₂ adsorption/desorption and UV-vis studies. These containers were incorporated into waterborne epoxy coating namely EP/CBS1 and EP/CBS2, respectively. Their performance was investigated in comparison to a reference coating EP/REF and coatings doped with commercial inhibitor zinc phosphate, EP/ZP. The surface morphology and adhesion of coatings were examined using OM, SEM and 3D profilometer. EIS measurements of scribed coating in 3.5 wt% NaCl solution for 48 h demonstrated high active corrosion resistance of EP/CBS1. However, EIS assessment of intact coatings for 30 d shows the dominance of EP/CBS2 with |Z|_{0.01 Hz} value of 6.0×10⁷ Ω cm2 after 30 d of exposure, a performance corroborated by salt spray test carried out for 50 d. Hence, driven by the large size and amorphous core of C@B@MSP2 which allows compatibility with the waterborne epoxy matrix, EP/CBS2 demonstrated a synergy between exceptional barrier properties and adequate active corrosion resistance implying their versatility. Therefore, in addition to inhibitor loading efficiency of containers, their sizes and compatibility of textural properties with the chosen polymer matrix is crucial for better performance as active carriers in waterborne anticorrosive coatings.