Water-Dispersible Silica-Polyelectrolyte Nanocomposites Prepared via Acid-Triggered Polycondensation of Silicic Acid and Directed by Polycations

摘要

The present work describes the acid-triggered condensation of silicic acid, Si(OH)(4), as directed by selected polycations in aqueous solution in the pH range of 6.5-8.0 at room temperature, without the use of additional solvents or surfactants. This process results in the formation of silica-polyelectrolyte (S-PE) nanocomposites in the form of precipitate or water-dispersible particles. The mean hydrodynamic diameter (d(h)) of size distributions of the prepared water-dispersible S-PE composites is presented as a function of the solution pH at which the composite formation was achieved. Poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) and block copolymers of DMAEMA and oligo(ethylene glycol) methyl 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 is also examined. The effect of polyelectrolyte strength and the OEGMA block on the formation of the S-PE composites is assessed with respect to the S-PE composites prepared using the PDMAEMA homopolymer. In the presence of the PDMAEMA(60) homopolymer (M-w = 9400 g/mol), the size of the dispersible S-PE composites increases with solution pH in the range pH 6.6-8.1, from d(h) = 30 nm to d(h) = 800 nm. S-PDMAEMA(60) prepared at pH 7.8 contained 66% silica by mass (TGA). The increase in dispersible S-PE particle size is diminished when directed by PDMAEMA(300) (M-w = 47,000 g/mol), reaching a maximum 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. Precipitated S-PE composites were obtained as spheres of up to 200 nm in diameter (SEM) and up to 65% mass content of silica (TGA). The conditions of pH for the preparation of dispersible and precipitate S-PE nanocomposites, as directed by the five selected polyelectrolytes PDMAEMA(60), PDMAEMA(300), PMOTAI(60), PDMAEMA(60)-b-POEGMA(38) and PMOTAI(60)-b-POEGMA(38) is summarized.