Interaction mechanism of ultrafine silica and poly(amido-amine) and dispersibility of the complexes in coatings

Ultrafine silicon dioxide was modified by NH2-teminated poly(amido-amine) (PAMAM) dendrimers to improve its dispersibility in the coatings. The complexes of nano-SiO2 and PAMAM were analyzed, and the modification mechanism was studied through density functional theory (DFT) in a gas phase with UB3LYP/6-31+G(d) and HF/6-31 G basis sets. Two stable conformers were gained: type A (Si+ was bound to the amine site) and C (Si+ was bound to the amide site), due to the chemical bond formation of SiN° and SiO, respectively. The electronic density population revealed the existence of the active binding regions such as the amide O and the amine N. The IR spectra for the lowest energy conformers was thoroughly analyzed and compared with the available experimental data.

The work is to optimize the complex configurations of PAMAM and SC on the basis of DFT theory.Figure optionsDownload as PowerPoint slideHighlights
► The dispersibilty of ultrafine silica in coatings is improved by PAMAM modification.
► The cleavage of SiO2 prefers to the heterolytic cleavage: Si+ (SC) and SiO− (SOA).
► The amide O, the amine N atoms are the preferred bonding or coordination sites.
► The hydrogen bonds and the spatial hindrance effect play an important role for stability.
► The orientation of the carbonyl O creates a favorable site for the complexation.