Formation and Physicochemical Characterization of Silica-Based Blackberry-like Nanoparticles Capped by Polysaccharides

Abstract

Strictly monodisperse 200-nm silica nanoparticles were hydrophobically modified (HM) by surface coverage with octadecanol. In successive stages, a graft copolymer was adsorbed. The graft copolymer was obtained by atom-transfer radical polymerization (ATRP). The polymer hydrophobic functionality consists of short pMMA [poly(methyl methacrylate)] units of controlled length and low polydispersity covalently linked to pullulan. Depending on concentration, it forms more or less densely packed layers on the surface of HM silica nanoparticles. The surface coverage density of these particles is modulated by the mole ratios between the components (grafted copolymer and HM nanoparticles) and is controlled by the solvent properties. The conditions used in surface coverage procedures, obtained by mixing the components in DMF and adding water in continuous elution gradient, give rise to uniformly polymer-grafted nanoparticles and to blackberry-like particles under saturation conditions. In such systems, the polar groups in the polymer chains face outward from the particles and give rise to corrugations on their surface. The surface morphology of the nanoparticles is tuned by controlling the amount of adsorbed polymer. In each stage of the surface coverage procedures, the resulting nanoparticles were investigated by DLS (in back-scattering mode) and SEM. The same holds for electrophoretic mobility results, which are rationalized in terms of a Langmuir-like adsorption isotherm.