Characteration and triggered release of ion-responsive poly (1-vinyl-3-ethylimidazolium tetrafluoroborate)@CaO microcapsules

The ion-responsive poly(1-vinyl-3-ethylimidazolium tetrafluoroborate) (PVEIm⁺BF₄^-)@CaO microcapsule was synthesized by phase separation. By the ion-exchange of BF₄^- on the poly(ionic liquids) (PILs) with Cl^- in water, the hydrophobic crosslinked PILs shell can be converted to hydrophilic and formed hydrophilic channels in water. The CaO in microcapsules can be released to water through the channels and transferred to Ca(OH)₂. The addition of PVEIm⁺BF₄^-@CaO microcapsule to NaCl solution can reduce the Cl^- concentration from 8.3 mmolL^-1 to 5.8 mmolL^-1 and increase the pH from 7.00 to 11.83 simultaneously. The release rate of CaO shows a direct relationship with ionic liquids (ILs) content and the mass ratio of styrene(St):divinylbenzene(DVB). The increase of Cl^- concentration can result in the increase of CaO release rate. The CaO can be completely released to NaCl solution from PVEIm⁺BF₄^-@CaO microcapsules consisted with different mass ratios of monomers or triggered by various concentrations of Cl^-. The maximum Ca²⁺ concentrations in the solution are similar, which is about 3.4 mmolL^-1. SO₄^2- can also trigger the release of microcapsule. The results show that the PVEIm⁺BF₄^-@CaO microcapsules are sensitive to Cl^- and SO₄^2-. The concentration ratio of Cl^-/OH^- decreases significantly after the PVEIm⁺BF₄^-@CaO microcapsules adding, which is beneficial to improve the corrosion resistance of steel bars to Cl^-.