pH-Responsive Hollow Polymeric Microspheres and Concentric Hollow Silica Microspheres from Silica−Polymer Core−Shell Microspheres

Abstract

Nearly monodispersed silica−poly(methacrylic acid) (SiO₂−PMAA) core−shell microspheres were synthesized by distillation-precipitation polymerization from 3-(trimethoxysilyl)propylmethacrylate-silica (SiO₂-MPS) particle templates. SiO₂−PMAA−SiO₂ trilayer hybrid microspheres were subsequently prepared by coating of an outer layer of SiO₂ on the SiO₂−PMAA core−shell microspheres in a sol−gel process. pH-Responsive PMAA hollow microspheres with flexible (deformable) shells were obtained after selective removal of the inorganic SiO₂ core from the SiO₂−PMAA core−shell microspheres by HF etching. The pH-responsive properties of the PMAA hollow microspheres were investigated by dynamic laser scattering (DLS). On the other hand, concentric and rigid hollow silica microspheres were prepared by selective removal of the PMAA interlayer from the SiO₂−PMAA−SiO₂ trilayer hybrid microspheres during calcination. The hybrid composite microspheres, pH-sensitive hollow microspheres, and concentric hollow silica microspheres were characterized by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and energy-dispersive X-ray (EDX) analysis.