Water-dispersible silica-polyelectrolyte nanocomposites prepared via acid-triggered polycondensation of silicic acid and directed by polycations.

The present work describes the acid-triggered condensation of silicic acid, Si(OH)4, as directed by selected polycations in aq. soln. in the pH range of 6.5-8.0 at room temp., without the use of addnl. solvents or surfactants. This process resulted in the formation of silica-polyelectrolyte (S-PE) nanocomposites in the form of ppt. or water-dispersible particles. The mean hydrodynamic diam. (d_h) of size distributions of the prepd. water-dispersible S-PE composites is presented as a function of the soln. pH at which the composite formation was achieved. Poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) and block copolymers of DMAEMA and oligo(ethylene glycol) Me ether methacrylate (OEGMA) were used as weak polyelectrolytes in S-PE composite formation. The activity of the strong polyelectrolytes poly(methacryloxyethyl trimethylammonium iodide) (PMOTAI) and PMOTAI-b-POEGMA in S-PE formation was also examd. The effect of polyelectrolyte strength and the OEGMA block on the formation of the S-PE composites was assessed with respect to the S-PE composites prepd. using the PDMAEMA homopolymer. In the presence of the PDMAEMA₆₀ homopolymer (M_w = 9400 g/mol), the size of the dispersible S-PE composites increases with soln. pH in the range pH 6.6-8.1, from d_h = 30 nm to d_h = 800 nm. S-PDMAEMA₆₀ prepd. at pH 7.8 contained 66% silica by mass (TGA). The increase in dispersible S-PE particle size was diminished when directed by PDMAEMA₃₀₀ (M_w = 47,000 g/mol), reaching a max. of d_h = 75 nm. S-PE composites formed using PDMAEMA-b-POEGMA remain in the range d_h = 20-30 nm across this same pH regime. Pptd. S-PE composites were obtained as spheres of up to 200 nm in diam. (SEM) and up to 65% mass content of silica (TGA). The conditions of pH for the prepn. of dispersible and ppt. S-PE nanocomposites, as directed by the five selected polyelectrolytes PDMAEMA₆₀, PDMAEMA₃₀₀, PMOTAI₆₀, PDMAEMA₆₀-b-POEGMA₃₈ and PMOTAI₆₀-b-POEGMA₃₈ was summarized.