SiOH-functionalized polystyrene latexes. A step toward the synthesis of hollow silica nanoparticles

Following a previous work (Tissot, I.; Lefebvre, F.; Bourgeat-Lami, E. Macromolecules 2001, submitted for publication), polystyrene latex particles containing silanol groups have been synthesized in emulsion polymerization using 3-(trimethoxysilyl)propyl methacrylate (NIPS) as a functional comonomer. The surface properties of the functionalized polymer latexes were investigated in depth using electrophoretic measurements and the soap titration method, Both techniques gave qualitative evidence of the presence of SiOH groups at the particles surface. The concentration of surface charges was quantified by potentiometric and conductometric titrations. As expected, the surface charge density increased with an increase in the pH and with an increase in the MPS concentration. Because of the presence of silanol groups at the particles surface, no loss of colloidal stability was observed when the functional polystyrene latexes were suspended into ethanol/water mixtures. The silanol groups were then converted into a 20 nm thick silica layer using a procedure derived from the Stober method (Stober, W.; Fink, A.; Bohn, E. J. Colloid Interface Sci. 1968, 26, 62). Hollow silica nanoparticles were finally generated by thermal degradation of the templating organic latex core. This work illustrates the determining role of interfaces in the structuration of organic-inorganic colloids.