Novel Method for Preparation of Structural Microspheres Poly(N-isopropylacrylamide-co-acrylic acid)/SiO₂

This paper presents a novel method for preparation of structural organic−inorganic hybrid microspheres with poly( N -isopropylacrylamide- co -acrylic acid) (P(NIPAM- co -AA)) as the core and nanosilica particles as the shell. The microhydrogel of P(NIPAM- co -AA) swelled with ammonium hydroxide was used as microreactor, and nanosilica particles gradually deposited on the microhydrogel from the surface to the inner part via hydrolysis and condensation of tetraethoxysilane in an n -heptane medium. The morphology, composition, and crystalline structure of the hybrid microspheres were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and thermogravimetric analysis methods, respectively. The results indicated that the shell of the complex microspheres consists of SiO 2 microspheres with about 300 nm. Moreover, the thickness of shell could be controlled by the depositing reaction of SiO 2, and the hollow microspheres with different thicknesses of the shell were also obtained after calcination of the composite microspheres at 550 °C for 4 h.