Size control of hollow poly-allylamine hydrochloride/poly-sodium styrene sulfonate microcapsules using the bubble template method

Abstract

In a Na₂CO₃ solution, poly-allylamine hydrochloride (PAH) is broken down into colloidal particles of carbamate ions (R–NHCOO⁻) and amino ions (R–NH3⁺) within a certain pH range. Daiguji et al. (H. Daiguji, E. Matsuoka and S. Muto, Soft Matter, 2010, 6, 1892–1897) reported that when CO₂ microbubbles nucleate in this solution, the colloidal particles of PAH stabilize the microbubbles via adsorption. In this study, we successfully controlled the microcapsule radius by changing the concentration of PAH in the Na₂CO₃ solution. The zeta potential of these PAH microcapsules is positive at pH = 8.5, thus allowing poly-sodium styrene sulfonate (PSS) adsorption on hollow PAH microcapsules and the synthesis of bilayer PAH/PSS. Furthermore, the bilayer PAH/PSS capsule solution was titrated until the pH is adjusted to 7.0. The bilayer microcapsules were stable at pH = 7.0, proving that these bilayer capsules can be potentially employed for medical applications. Nevertheless, the success of bilayer fabrication strongly depends on the mass ratio of PAH and PSS. The decrease in the mass ratio of PSS results in irreversible flocculation. On the basis of the analysis of the zeta potentials and Fourier transform infrared-attenuated total reflection (FTIR-ATR) spectra for hollow microcapsules of both PAH and PAH/PSS, we elucidated the adsorption mechanism of PSS onto hollow PAH microcapsules.